Specs: 7.62x51mm versus .308 Win w/ diagrams (MERGED)

[TideWater 41009]

According to the March 2001 issue of Guns & Ammo magazine, and quoting from page 26, regarding the .308 Winchester; "Chamber pressures are 52,000 cup by the copper crusher method and 62,000 psi using the transducer method. That's up slightly from the values for the .30-06, but a little below maximum magnum pressures".

There seems to have been a lot of interest in this subject in past postings. I think there has been some confusion resulting from getting cup and psi mixed up. Hope this helps.


[ November 20, 2001: Message edited by: EMDII ]

[Scott S]

Yes, this topic is of interest to me. Appreciate you posting the info.

When I get around to it, I'll holler at a few ammo manufacturers to see if they load their 308 to 62,000 PSI MAP or a little milder in deference to arms chambered for 7.62 NATO.

Again, thanks.

Scott

[Scott S]

Got replies from Hornady and Federal. See my reply to JoeDoe's "New to FAL's" post in the General forum for the scoop.

[FINNWOLF]

Very good discussion of the difference in the cartridges. Is your point then that reloaders should try to duplicate the military load? Any suggestions?

[Uncle Buck]

The point is that you get a different pressure number for .308 Winchester depending on which gauge you choose to measure it with. You get 52,000 PSI with the copper crusher gauge, which is known as copper units of pressure (cup) and you get 62,000 PSI for the same loading of the same .308 Win with the piezoelectric transducer gauge. The use of these two different gauges by the US military (copper crusher) and the commercial SAAMI specs (piezo) is responsible for the fictitious net rumor that .308 is loaded to much higher pressures (62,000) than 7.62 NATO (50,000). They are actually loaded to approximately the same pressures when you measure with the same gauge (50,000 vs 52,000 PSI). Die rumor, die!
UB

[Scott S]

Uncle Buck, I think your post isn't entirely accurate. Let me try to explain.

You are correct that you get different numbers depending on the measuring method you use. However, you can't get PSI from the copper crusher measuring method, nor can you get CUP from the piezoelectric transducer method. When one uses the copper crusher method, one *always* gets a pressure value in copper units of pressure (CUP). When one uses the piezoelectric transducer, one *always* gets a pressure value in PSI. There are no exceptions, nor is there a formula to convert from CUP to PSI, or vice versa.

So, the first post in this thread, from RefinishGuy, is accurate. It states that the chamber pressure for .308 Winchester is 52,000 CUP or 62,000 PSI, depending on the measuring method. Those two values are approximately the same; it's just the units of measure are different. It's kinda analogous to measuring the length of an object with a metric ruler and a standard ruler. A .308 cartridge case is 51mm long using the metric scale and 2.010 inches long on the standard scale. Same length, different measuring units.

So, if we compare apples to apples, it seems we do find that there is a difference between the .308 and the 7.62. Per the first post, .308 Winchester is loaded to 62,000 PSI (as measured by piezoelectric transducer). Per page 11-3 from the Army Tech Manual TM43-0001-27 (June 1981) that Dano posted on September 10th of last year, the 7.62 is loaded to 50,000 PSI (also measured by piezoelectric transducer). Comparing pressure of the two rounds as measured by copper crusher, the .308 is 52,000 CUP and I the 7.62 is around 44,000 CUP (sorry, can't cite a source for 7.62 in CUP, but I remember seeing it somewhere around that figure).

For confirmation of this info, check out page 57 of the online reloader's guide at www.AlliantPowder.com. (http://www.AlliantPowder.com.) That page lists the pressures, as measured in CUP *and* PSI, for several common rifle loads shown in their guide. They list their loads for the .308 at 52,000 CUP and 60,000 PSI (2000 less than SAAMI spec on the PSI scale). A couple other loads they list are:

30-06 at 50,000 CUP and 60,000 PSI
7mm-08 at 52,000 CUP and 57,500 PSI
.222 Rem at 46,000 CUP and 50,000 PSI
7x57 Mauser at 46,000 CUP and 51,000 PSI

Although the CUP and PSI numbers are different for each cartridge, the pressure is approximately the same. (I say approximately because there are slight accuracy variations that make exact measurement essentially impossible.) I listed those loads to show that there really is no way to convert CUP to PSI or vice versa. Though the .308 and the 7mm-08 read the same pressure in CUP, 52,000, each cartridges' value in PSI is different. I dunno why.

Did all that BS make sense to anyone?

FINNWOLF, to answer your question, I think it's probably a good idea for reloaders to stick to milder loads for the FAL to extend brass life and perhaps the life of the gun. While I do reload and brass is a concern for me, my bigger concern is the gun itself. My point there is that I haven't found enough info to state conclusively that shooting .308 in an FAL really isn't a good idea. Is it worth all the ink I've spilled to worry about it? Maybe not. Perhaps I should just shut the hell up and shoot.

Thanks for the input/questions.

Scott

[Uncle Buck]

Your understanding is pretty close, but there still are some inaccuracies. First of all, all pressures are in units of force per area and in the US that is pounds per square inch. It is Newtons per square meter in the metric world. The differences in the gauges measurements arises from the different way they perform in a kinetic measurement (rapidly changing pressure) versus their static (constant pressure) performance, which is how they are calibrated. The Piezo gauge more accurately reflects its calibration in a kinetic measurement.
Since the copper and piezo gauge respond differently, they read different pressure values. Both values are in PSI, but to make it clear that the measurement methods have different values, the copper method is called copper units by convention (and the units of pressure are always PSI). The piezo method is not always specified, since it is more accurate, but it should be called piezo units or transducer units. There is no simple mathematical transformation for the two measurements, so a direct comparison of the numbers is invalid, although you used to find this comparison used on the net to claim that .308 is loaded to much higher pressure than 7.62. This is a net rumor that needs to die.
UB

[Scott S]

UB, I'm trying to understand what you're saying. (I'm an English major, so please bear with me.)

I don't consider Guns & Ammo the ultimate authority on guns, but I assume they pulled their 62,000 PSI number for .308 chamber pressure from SAAMI specs or a source that has access to the $35 book with SAAMI specs for common US rifle cartridges. Surely they aren't trying to mislead their readers. Sound reasonable?

The US Army source I cited in my earlier post lists the pressure for the 7.62 as 50,000 PSI. That spec says nothing about CUP, but on the other hand, nor does it state what measurement method was used to come up with the 50,000 PSI number.

So, given that both these sources *seem* reliable and the difference between the two numbers is 12,000, are you saying that the Army is using the copper crusher method but reporting their findings in PSI and that's what accounts for the difference between the cartridges? Or have I missed your point entirely?

If the Army is using copper crusher and reporting that as PSI, that sounds dangerous. It's also contrary to all labeling of US cartridge pressure data I've seen. When a manufacturer measures using the piezoelectric method, PSI is the only label used.

I do understand that there is inherent inaccuracy of "measuring" dynamic pressure by comparing to static calibration. However, the 2,000 PSI difference you cite is fairly significant, much less 12,000 PSI. I don't think inherent error can account for that much difference.

I look forward to reading your reply.

[Uncle Buck]

I trained in physics :-) Remember, pressure units are always force per unit area. This is just one of those laws of physics, just like units of speed are always distance per unit time. Listing a number as PSI doesn't tell you anything about how the number was measured. The US military continues to use the copper crusher gauge, since they have used it for 100 years, so their PSI numbers are all cup. SAAMI uses the more accurate piezo transducer gauge, so their PSI numbers are different and not directly comparable to cup PSI numbers. The point is that if you don't use the same gauge or measurement system, the comparison of the numbers is not valid, since one gauge reads 52,000 PSI and the other reads 62,000 PSI on the same firing.
UB

[Scott S]

OK, now I see what you're saying. So, although the US Army lists their measurement as 50,000 PSI for the .308, they use the copper crusher method to take their measurement, and they mistakenly label that measurement PSI instead of CUP.

Although that sounds seriously suspect to me, I can't refute that. I'll look for info that states exactly what measurement system the US Army/military uses and report if I find anything.

I do take issue with your statement, "Listing a number as PSI doesn't tell you anything about how the number was measured." Perhaps this doesn't hold true for the US military or for European countries, but here in the US, per SAAMI, labeling cartridge pressure as PSI means it was measured using the piezoelectric method, CUP by the copper crusher method, and LUP by the older lead crusher method. Reloading manuals do not deviate from this practice. I can't imagine the consequences of measuring a .308 rifle load at 51,000 units of pressure using the copper crusher method, labeling that value as PSI, and publishing that finding. Novice reloaders might then assume that the top load listed reached only 51,000 PSI, 11,000 PSI short of SAAMI max, and try to load hotter, with perhaps disasterous results.

I do agree with your statement that one can't compare cartridge pressure values measured with different methods.

Good discussion. Thanks.

Scott

[Wadman]

Unless Uncle Buck is saying that the Army tested using the copper crusher but listed the pressure using the PSI equivalent of the CUP rating. Either way, I have to believe that if the difference were that great, all the books and magazines and ammo retailers would not use the terms so interchangeably. Right? If it was actually 12,000 units of difference, I think they'd go to much greater pains to distinguish the two.

A good example is the 8mm Mauser discussed in an old thread. The weak 1888 (.318) loading is simulated in the US by keeping it at 37,000 CUP. Full power .323 loading data pushes it to 50,000 CUP. So if a difference of 13,000 CUP is considered a very dangerous difference between those two loadings, you would think the same would apply to 7.62 Nato and .308 Win.

PS I got the above info from Speer #11 manual.

[Uncle Buck]

The conceptual problem that many of you are still having is that all these gauges give pressure numbers in PSI. That is because they are all calibrated in PSI and we always use PSI in the US as units of pressure. The problem is that just because you see a pressure listed (and it is always PSI in the US) it doesn't always tell you how it was obtained.

50,000 cup is 50,000 PSI obtained with the copper crusher gauge.
50,000 lup is 50,000 PSI read with the lead crusher gauge.
50,000 PSI with the piezo transducer is ambiguous because they don't tell you how it was obtained. The reason that they don't list the method is that the dynamic readings obtained with this gauge are very close to the actual static calibration in PSI. Still, to avoid invalid comparison problems, the method should have been listed, like piezo units of pressure or transducer units of pressure.

If you want an analogy, it is like having two different tire gauges, a pen type and a dial type. The two gauges may give different readings on the same tire because they have different inherent accuracies, but they both read in PSI.
UB
UB

[Scott S]

If all these gauges give pressure numbers in PSI, then it seems we have a little 12,000 PSI discrepancy between the figures published by Guns & Ammo:

According to the March 2001 issue of Guns & Ammo magazine, and quoting from page 26, regarding the .308 Winchester; "Chamber pressures are 52,000 cup by the copper crusher method and 62,000 psi using the transducer method..."

According to your last post, the 52,000 figure G&A lists is actually PSI.

If all these readings from manufacturers and the military are in pounds per square inch (PSI), then why do they persist in using the terms copper units of pressure (CUP) and lead units of pressure (LUP)?

[Uncle Buck]

That is correct: the copper gauge reads 12,000 PSI lower than the piezo transducer gauge for the same firingof a single cartridge when they are both used simultaneously. The military probably uses the old crusher gauge because it makes it easy to compare the performance on newly manufactured ammo to the standard when 7.62 NATO was originally adopted and the only way of measuring pressure was with the copper gauge. SAAMI probably uses the transducer because its reading is closer to what the peak pressure actually is.
UB

[W.E.G.]

OK. So can we get somebody to take a few rounds of Radway Green 7.62 and run it through the copper crusher and the piezoelectric thingy? Then we run a few rounds of Winchester 150 grain silvertips throught the same instruments. Then we compare the data.

All this technical and theoretical stuff sounds fine. Can we get some empirical DATA??? Seems to me that should settle the issue.

[jason h]

Scott S was orginally right for the most part. The copper crusher method uses a small copper cylinder that is exposed to the chamber pressures. When the cartridge is fired, pressure from the cartridge crushes the copper cylinder to some degree. Basically, the cup measurement is based on the change in length of copper cylinder after it is crushed. It is not in units of pressure but in units of deformation I believe. The problem with the cup method is that it only gives you a correlation of peak pressures to that of other cartridges not actual pressures.

The transducer method uses a strain gage that is attached to the chamber, and actually measures the strain in the barrel around the chamber as the cartridge is fired. Through a bunch of equations, it can then be determined what the pressure must be in the cartridge. The nice thing about this test is that is gives you the actually pressure curve over time and not just a correlation of peak pressures. The cup test is easier to do and has been around longer than strain gages. As far as I know there is no equation to convert from one system to the other since the measurements are based in completely different units(pressure versus length). Once again to clarify, the copper crusher method does not measure actual pressure, but gives a correlation of pressures among different cartidges.

As a side note, PSI stands for pounds per square inch. The cup number is not in units of psi but in units of cup.

[Uncle Buck]

Jason,
While you are correct that the copper gauge directly measures the length of a copper slug, the piezo gauge only directly measures a voltage across a strain gauge. In order to convert the direct length or voltage measurement into a pressure, you have to calibrate the gauges. You put a known (static or constant) pressure on the gauge and record its length or voltage. You create a table or list of pressure versus length or voltage to convert the direct length or voltage measurements into pressure (remember; if it is a pressure, its units are must be PSI no matter what gauge is used). Copper units of pressure or cup are PSI just like the numbers you get from the transducer gauge are PSI.

Gary,
The empirical test has been done and it was published in the 1985 volume of the Lyman handloading manual. They did simultaneous transducer and copper gauge measurements on .30-06 and showed that the copper gauge reads 12,000 PSI lower than the transducer gauge. This is rocket science.
UB

[Scott S]

UB,

Does it strike you as odd that Lyman came up with 12,000 PSI difference using the two pressure testing methods? If they are measuring PSI with both methods, why not calibrate the instruments to read closer together? Given the chamber pressure for the 30-06 is around 60,000 PSI (as measured by piezoelectric transducer), 12,000 PSI is a whopping 20% error. Surely Lyman (and other manufacturers) can calibrate their instruments better than that.

I still say either I'm drunk or you're wrong.

Gary,
I've been looking for some empirical data on the pressure testing method employed by the US military, but I haven't found any, yet. When (if?) I do, that should settle this issue. The closest thing I've "found" is the page from the Army manual that Dano posted last September, stating that the 7.62 is loaded to 50,000 PSI. However, it didn't state what measurement method was used (though I think it was the piezoelectric transducer method, not the copper crusher method).

As for testing at the range, both those methods are beyond my fiscal means. The only thing I can think of is to shoot both 7.62 and .308 loads on the same gas setting and see if the brass is thrown different distances. While that wouldn't tell you what the pressure is, it might give some indication of whether one load is hotter than the other. Or it might not.

I'm open to ideas.

[Uncle Buck]

Scott,
The discrepancy between the two gauges has to do with their different response factors when measuring a kinetic or rapidly changing pressure. If the gauges were only used to measure static or constant pressures, like the pressures that were used to calibrate them, they would give the same pressure value. In a kinetic measurement, the idea is to measure the peak pressure. The response time of the copper gauge is much slower than the piezo gauge, it it misses the peak. The piezo gauge is much faster, so it reads the peak more accurately. The situation is exactly analogous to using an analog DC voltmeter and an oscilloscope to measure a 60 cycle AC voltage. The voltage changes faster than the meter needle can swing, but the electron beam of the oscilloscope has no problem keeping up with the voltage change.
So, to summarize the different readings are not due to calibration or inherent accuracy differences, but due to the different response times of the gauges when they are used to measure a rapidly changing pressure.
HTH
UB

[TideWater 41009]

When all is said and done, regardless of how the pressures are measured, the average commercial .308 Winchester loading with a 150 grain bullet is listed at 2830 fps out of a 24" barrel, which is almost exactly the same as the 147 grain NATO load (although the barrel length is not given for the NATO load IIRC). Therefore, I think it is reasonable to surmise that the pressures must be nearly the same too.

Even so, pressure curves could still vary somewhat from one manufacturer's ammo to the next, and might require different gas regulator settings or eject the fired brass to a lesser or greater distance.

Or so it seems to me.
Refinishing Guy.

[Wadman]

And then there's the small matter of the slightly greater case capacity of commercial brass versus the thickwalled military brass. Anyone remember the warning in reloading books about using military brass? You're supposed to reduce charges because the slightly smaller combustion chamber could yield increased pressure.

Now you can keep on arguing about CUPs, PSIs, LUPs, and BVDs, but I'm going to continue to use 7.62N and .308 Win interchangeably.

[Uncle Buck]

The nearly equivalent ballistics of 7.62 NATO and commercial .308 Winchester are the reality check on the fact that the pressures are the same too, even though the published pressure numbers are way different. The commercial ammo manufactures would have to be real idiots to load their ammo to 12,000 PSI higher pressure to achieve absolutely nothing in terms of performance. Attorneys would be rejoicing at their stupidity. You can be sure the manufacturers are not stupid or the lawsuits would have bankrupted them by now.
UB

[WireGuy]

Originally posted by gary.jeter:
OK. So can we get somebody to take a few rounds of Radway Green 7.62 and run it through the copper crusher and the piezoelectric thingy? Then we run a few rounds of Winchester 150 grain silvertips throught the same instruments. Then we compare the data.

All this technical and theoretical stuff sounds fine. Can we get some empirical DATA??? Seems to me that should settle the issue.

What are you trying to do?
Confuse us with facts?
What, and ruin a good argument?
You Bastard!

(actooooly, it's a good idea.)

My understanding, (dim), is that one of the
reasons SAAMI used the transducer guages is
that it's much quicker and cheaper to do the tests.

Good thread, keep it up.

WireGuy

[Scott S]

Is there a formula to convert BAR to PSI or vice versa?

If so, I have some interesting findings. If not, I'm hitting the bottle again.

[Scott S]

I found a few places with BAR to PSI conversion formulae, so it seems one can convert between the two. I used the conversion computer at www.cruffler.com (http://www.cruffler.com) (the conversion factor is about 14.5 PSI per BAR).

Tool over to http://www.border-barrels.com/pressure/pressure.htm

There you'll find info on pressure testing of throat variances that "Pressure Trials Consortium" performed on the .308 Winchester cartridge. As part of their control group, they measured the pressure of Radway Green. You have to download the zip file to get at the info, but there's one chart, Pr-rg.gif, that shows pressures of RG tests in BAR. The peak mean pressure shown for RG in the control barrel is about 3650 BAR (I say about because the graph lists pressure increments in 200 BAR, and it's kinda difficult to tell exactly), which equates to 52938.87 PSI, per the Cruffler computer.

They do list the test instrument as a piezoelectric transducer. However, their test methods conform to the European CIP standard. I don't know if the CIP piezoelectric transducer measurements are comparable to the SAAMI piezoelectric transducer measurements. If they are comparable, we have a pressure difference of around 9,000 PSI between RG 7.62 and SAAMI MAP for .308.

Interestingly, the webpage http://www.yugoimport.co.yu/products/caliber_762.html lists a type 1 proof load for the 7.62 NATO as 60,900 PSI. Unfortunately, that page doesn't state what test method they use.

Comments?

[Wadman]

Scott S,

I remember reading somewhere, probably an old Guns'n Ammo, that there is a difference between the European CIP and SAAMI transducer methods. Are they trying to make things difficult or what?

[Scott S]

Wadman,

You're right, there is a difference in the way the two methods measure the pressure. Question is, are those differences so significant that comparing PSI measured by each system is worthless? My guess is that UB will say yes. My answer is that I simply don't know. They are making it hard on us.

FYI, I read several posts from the thread here: http://ns.shelfspace.com/~c-r-ffl/archives/199612/msg00409.html

Seems this group also looked at this question and found similar barriers to uncovering comparable pressure information. One guy even wrote SAAMI and a slew of US ammo manufacturers looking for answers; poor fellow came up with essentially nothing for all his work.

[jason h]

Hey UB, I agree with some of the things you have discussed, but I am still certain there is a real difference in pressures between sammi and nato loads. Yes strain gages can be calibrated by using known pressure loadings, and this does make your measurements more accurate. However, most strain gages come with listed gage factors which allow you to calculate strain with a measured difference in voltage. This however is somewhat trivial to the original discussion.

I am still convinced that the copper crusher method gives units of cup which are not a pressure unit but a yardstick unit of sorts. Also, pressure does not have to be in units of psi. There are a large number of different units for pressure, such as BAR, Pascal, psi, atm, torricelli, or inches of mercury. Naturually all these different units of measure are all not equal to each other. For instance 1 atm = 14.7 psi. So even if cup was a unit of pressure, there is nothing to prove that 1 cup = 1 psi.

I found this article here http://www.reloadbench.com/gloss/cuppsi.html
which seems to clear up this issue pretty well with regards to differences between cup and psi as measured using a strain gage.

[TideWater 41009]

Uncle Buck is correct when he said the old CUP method of measuring pressure was in units of PSI. When the CUP method was developed, the ballisticians believed that the CUP pressure tests were accurately providing PSI data. It was only relatively recently learned that their test results did not provide actual chamber pressure in PSI.

The copper crusher method is still used and is a valid and usefull means of ammunition development, but it does not actually express pressures in PSI. When ballisticians became aware of this they began to use the more descriptive term CUP instead of PSI, but the term PSI had become so widely used that it was commonly interchanged with CUP OR LUP. This was technically wrong but since everybody was talking about the same thing (CUP), it didn't matter.

When the electric strain gauge became available the actual chamber pressure in PSI became known and is now commonplace. Still, many data labs still use the crusher test system, including the US military. EACH SYSTEM PRODUCES DIFFERENT NUMBERS FOR THE SAME PRESSURES. Confusion has resulted from these souces that do not bother to provide the correct CUP or LUP designation.

When using similar weight bullets, the .308 Winchester and the 7.62 NATO are identical, for all practical purposes, in ballistics and pressure. If you still do not believe this, ask yourself, "Why would commercial manufacturers load to higher pressures to achieve the same ballistics?"

The European manufacturers' tests are done differently, and only further add to the PSI confusuion.

Interesting thread. Thanks to all responses.

Refinishing Guy

[Wadman]

And to add to Gunthing's post....

If the difference was truly 12,000 units of pressure (CUP,PSI,LUP, whatever), wouldn't the ammo manufacturers take greater pains to distinguish the two? After all, they DO take pains to distinguish .38SPL and .38 +P SPL which has less of a difference than 12,000 units of pressure.

================================================== =======

I dont' know if this issue will ever be adequately resolved. In the end, it's going to come down to what you feel comfortable with. My rifles are marked .308 Win and DSA even commented on this board that their rifles are chambered using those specs. Either way, these are versions of military weapons with a reputation for toughness and longevity. I'm certainly comfortable using either type of ammunition. If you aren't, then stick with 7.62 Nato and don't worry about anything else. You're certainly not going to hurt anything being conservative.

[This message has been edited by Wadman (edited February 07, 2001).]

[Scott S]

And therein lies another problem. What are the ballistics of NATO and 308 loads? Unfortunately, I have no chronograph, otherwise I'd happily test several different loads for velocity.

I don't think that 7.62 loads achieve the same velocity as US manufacturers' .308 loads. Close, yes, but not the same. I read an article in Shooting Times (summer of 2000? don't remember the month, tossed the issue months ago) where the author, Rick Jamison, did a comparison of velocity and pressure in .308 Winchester loads. Interesting thing was that pressures well over SAAMI limits didn't make much difference in velocity. So, stating that 150 grn 308 loads at 2780 fps and 147 grn 7.62 loads at 2750 fps develop similar pressures can be inaccurate. The two loads might be very near the same pressure, but on the other hand...

[Scott S]

Wadman,

Seems like your supposition makes sense, but remember that commercial, US ammo manufacturers are loading to SAAMI specs for firearms manufactured by SAAMI members and military ammo manufacturers are loading to mil specs for mil spec guns. The military doesn't fire commercial ammo in its guns, so there's no need to include warnings on military firearms about firing commercial ammo that might develop higher chamber pressure. Should Entreprise and DSA, because their guns are of military origin, include warnings on their guns about firing 308?

Hmmm. Who loads 7.62x51 for the US military? Do any commercial manufacturers, such as Winchester, Federal, or Remington, have contracts to the US military for 7.62 ball ammo? If so, it would be interesting to know whether they use the same pressure testing equipment for military and commercial loads and whether they follow the specs on paper for 7.62--50,000 PSI.

[BUFFLER]

Winchester and Federal both make and sell .223/.5.56 to the miklitary. I know Winchester does 7.62.

BUFFLER

[TideWater 41009]

Originally posted by Scott S:
...I've been looking for some empirical data on the pressure testing method employed by the US military, but I haven't found any, yet. When (if?) I do, that should settle this issue. The closest thing I've "found" is the page from the Army manual that Dano posted last September, stating that the 7.62 is loaded to 50,000 PSI. However, it didn't state what measurement method was used (though I think it was the piezoelectric transducer method, not the copper crusher method).

As for testing at the range, both those methods are beyond my fiscal means. The only thing I can think of is to shoot both 7.62 and .308 loads on the same gas setting and see if the brass is thrown different distances. While that wouldn't tell you what the pressure is, it might give some indication of whether one load is hotter than the other. Or it might not.

I'm open to ideas.

THE MYSTERY IS SOLVED! According to the NRA, the U.S. military uses the copper crusher method to measure pressure. Also, the muzzle velocity for 7.62 NATO is actually about 2808 fps, not 2750 fps as stated above and elsewhere. 2750 fps is the instrumental velocity measured at 78 feet from the muzzle.

Different gas setting requirements for different manufacturers and types of ammo only indicates a difference in port pressure, and may or may not have any relationship to peak chamber pressure.

Refinishing Guy.

------------------
"A man not shackled with the truth can win any debate."

[Scott S]

Hey Refinishing Guy, thanks for following up. So, they're actually measuring 50,000 CUP, not PSI. In that case, SAAMI specs and US Mil specs differ by only 2000 CUP, not enough to make any difference to me.

Oh, and good catch about my incorrect supposition regarding the distance brass gets thrown relating to chamber pressure. I don't know what I was thinking when I wrote that.

Touche, Uncle Buck!

[TideWater 41009]

Originally posted by Scott S:
...So, they're actually measuring 50,000 CUP, not PSI. In that case, SAAMI specs and US Mil specs differ by only 2000 CUP, not enough to make any difference to me.


Scott S; Actually, to be 100% technically correct, the pressure for NATO ammo should be expressed as "50,000 p.s.i., as measured by the c.u.p. method". C.u.p. is a p.s.i. measurement, but it measures pressure differently (static) than a strain gauge (dynamic). Both systems measure p.s.i. accurately, but the numbers are different because they measure pressure in a different manner.

Bottom line; .308 Winchester commercial ammo uses thinner cases, is loaded to about 5% greater pressure, and gives about 40 f.p.s. higher muzzle velocity than 7.62 NATO. 7.62 NATO ammo is generally held to slightly smaller dimensional tolerances than .308 Winchster. Other than this, the two cartridges can be considered identical when both are loaded with 150 grain (approx.) bullets. The real differences between the two caliber designations is the headspacing of the chambers of the rifles in which they will be fired. SAAMI headspace spec is generally regarded as between 1.630" and 1.634", which also works perfectly with NATO ammo. NATO specs are much looser, and the maximum Field Reject limit is a whopping 1.6455"!!! With the thick brass used in NATO cases this is perfectly safe, but it would be extremely dangerous to fire .308 Winchester commercial ammo in such a rifle or machine gun. As long as your rifle is headspaced to the middle of SAAMI specifications (approximately 1.632"), you can safely shoot either .308 Winchester OR 7.62 NATO in it.

You might want to check out http://www.fnfal.com/forums/Forum3/HTML/001657.html

Refinishing Guy.

------------------
"A man not shackled with the truth can win any debate."

[This message has been edited by RefinishGuy/GunThings.com (edited April 06, 2001).]

[Uncle Buck]

Touche?

OK, one more time: The Units of Pressure (the UP in CUP) in the US are Pounds per Square Inch. 50,000 CUP means 50,000 PSI as measured by the copper crusher gauge.

Any pressure units can be readily converted to any other unit of pressure simply by multiplying by a constant. Examples would be converting Bar to PSI by multiplying by 14.5. This is exactly the same as any units of speed can be converted to any other units of speed. You can easily convert FPS to MPH or meters per second by multiplying by a constant.

Since the copper gauge and the piezo gauge both give pressures in the same units (PSI!) no conversion is necessary, but the comparison of the pressure values is invalid as the gauges don't give the same reading.
:D

[Scott S]

Yep, touche Uncle Buck. Thanks for remaining patient with me while I ranted about which I know not. I think I *finally* understand. Thanks, too, to the Refinishing Guy.

Seems damned foolish to label a pressure CUP when it's really PSI. If it's the measuring method that's different (and not the units of measure) then why don't manufacturers state "XX,XXX PSI as measured by the copper crusher/lead crusher/transducer method" when referring to the pressure of their ammo? Grrrrr.

It's like trying to determine why half the bolts on my Chevy are metric and the other half standard--utter futility.

[Uncle Buck]

What is foolish or irrational is that the transducer measurements are not labeled "Piezo Units of Pressure" or "Transducer units of Pressure". If they were labeled PUP or TUP, then there wouldn't be all this confusion with CUP.

[W.E.G.]

btt

[Muggzy]

I did a velocity test on Hirtenber,Radway Green and South African. Those numbers are under "Ammo" "velocities". You guy are scarin the hell out of me. I'll just do the chrono thing.
Seems I have read here that other guy have shot Winchester and Remington .308 through their FAL's and I don't remember any problems being reported.

[gman]

Weeeelll, if you look on page 404 of the A-Square reloading manual Art Alphin lists 150 grain loads in PSI and 180 grain loads in CUP. Oh well. At 51,900 psi with 46 grains of IMR-4064 velocity is 2802 fps. Whaddaya know.

I have reloaded using velocity as the main determinant. A given pressure will return a given velocity up to a point. By loading under, then working up, you reach a listed max velocity load in the books. Don't go over. I have found many times I would reach a listed max before I came near a listed load weight of powder. This is simply due to variations in barrels.
Speaking only for myself, when I find a load listed in CUP or PSI I work out a proportion and only for that cartridge. 50,000 CUP and say 60,000 PSI gives me 1.2. Divide the PSI by this or multiply the CUP by this. It is an easy rule of thumb and only that. I use it to get into the ball park and ALWAYS use my chronograph. Chronys can be had for $89.00 on sale, there is no excuse not to get one. I you want a definitive answer you can get an Oehler set up that'll run around a $1,000 but it is wth the pressure transducer system so you can set it up for your rifles.

"According to the March 2001 issue of Guns & Ammo magazine, and quoting from page 26, regarding the .308 Winchester; "Chamber pressures are 52,000 cup by the copper crusher method and 62,000 psi using the transducer method. That's up slightly from the values for the .30-06, but a little below maximum magnum pressures". Gunthings.

110% correct, the reason it is loaded a little hotter that the '06 is 'cause the Army wanted to maintain the same ballistics as the '06 but in the shorter package to use in the M-14. Pic o page 401 of A-Square manual shows en bloc clip of '06 next to open port of M-14 and the .308 (or Ordnance T-65 as it was called) allowed for a 1 inch shorter receiver.

[ November 08, 2001: Message edited by: gman ]

[Arado]

After doing considerable research into this topic I have found only one salient difference between .308W and NATO 7.62. Commercial .308W cases are cheaply made with thin walls to lower cost of production. Nato cases are heavier walled to accommodate "generous" chambers. The vast majority of .308W is loaded to app. 47k and Nato is constrained to a "max" of 50k whereas actual loading avg. at 47k. Bottom line is do not use .308W in "generous" military chambers due to case failure caused by not enough brass to flow and seal. Gar

[thacket]

Greetings,

Excellent discussion. I am new at this, so please don't throw too many rocks. Could you do a rough cross check by working backwards? What I mean is, you know the powder load, loaded case volume and powder characteristics for bullets of equivilent weights for both .308 and 7.62x51. If these different cartridges are fired from the same gun and chronographed, would the muzzle velocities be close? Would the .308 be slightly faster? If they are close, with everything else known about the other charachteristics, would the pressures be close regardless what units are used? Does what I am saying make sense? Will Hortense run off with Roger? Tune in next week.... Well, you get the idea. Thanks for listening.

All the Best,
John

[Viking Warrior]

from 303 British.com

7.62x51mm NATO or 308 Winchester?
An Armourer Explains the Differences
Do you have a military surplus rifle chambered in 7.62 x 51mm? If so, I'll bet part of the reason you bought it was to get a "308 Winchester" at a really low price. Well, you screwed up. It's like looking at a Northern Pike and a Muskie. They're close yes, but each is distinctive, and you have to understand what you're looking at.



--------------------------------------------------------------------------------

Early in my military career, I worked on the FNC1 rifle (7.62 NATO). For someone that had previously handled and fired only shotguns and hunting rifles, this was a real treat! Maybe being an armourer wasn't going to be that bad! It was only natural then, that curiousity would generate questions and comparisons about what I thought was the same cartridge - 308 Winchester and the 7.62x51mm NATO.
As part of my personal battery, I had a Midland 2100 chambered for 308 Winchester. This rifle was made in England by a small company - Midland Rifle Co I believe - but owned by Parker Hale. Having lots of military 7.62x51mm rounds available, I shot them from my 2100 from time to time. There was never a problem chambering or firing the military stuff. It was a pleasant diversion over the long (read boring) periods spent at the range for base small arms qualifications.
(I traded it off some years ago for a Smith & Wesson Model 686. It's the only rifle I ever regret losing! - Steve)

Around this period I discovered that shooting reloaded cases fired from an FN was virtually impossible. They didn't want to chamber. My frustration led me to ask an older armourer what was wrong. In a nutshell, he told me that they probably didn't fit because they stretched. I was using a Lee Loader in 308 Winchester and didn't know that they only resized the neck, leaving the rest of the case untouched. The shoulders were blown forward on initial firing, so the case was simply too long to fit my rifle's chamber! Hmmm...
I tried the gauges from work in my own rifle. What a shock! None of them would fit! The corporal brought a set in from home and explained the difference. Here's what I discovered.

308 Winchester (SAAMI) Gauges Shop (Military) Gauges
GO - 1.6300" GO - 1.6350"
NOGO - 1.6340" NOGO - 1.6405"
FIELD - 1.6380" FIELD - 1.6455"

The gauge sets were different too! What gives? He told me that the dimensions of the two new and unfired cartridges were basically the same. The difference lay in two areas - chamber size and cartridge makeup.

Chamber Size
Look at the picture below. The top chamber represents a military rifle, the bottom one a commercial sporter. With many military rifles, their chambers can be significantly longer than, say, a Remington 700. Note that the military chamber would fail a NO GO check, but pass a FIELD check using the proper shop (military) gauges.

There is a .013" difference in chamber length however, between these two "Safe & Serviceable" rifles!

http://www3.sympatico.ca/shooters/rimless2.JPG
There will be distinct differences between chambers of military rifles based on:

Type
Ishapur, Garand, FN etc.
Amount of Use
Condition at Time of Sale
Just by looking at the dimensions, you can see that using SAAMI gauges is bound to reveal "problems".
Cartridge Makeup
I said at the beginning that these two cartridges were basically the same, dimensionally. While they may share similar external measurements, there is one major difference that you can't see. Case wall thickness.

http://www3.sympatico.ca/shooters/thickness.JPG
Military brass is thicker. It needs to be. It was made to function and stretch in a wide variety of firearm chambers. Don't forget that the condition of spent brass is of no importance to the service. Like 99% of military brass, it won't be reused.
Where does that leave you? Follow this rule and you won't have any problems.

DON'T USE YOUR RIFLE IF IT FAILS THE SAAMI FIELD CHECK!!

Why not? Right away you know that the chamber is measuring more than 1.6380" (SAAMI FIELD) - possibly more. It will stretch by a minimum of .008" on first use! Probably more. It may even rupture! You must get the headspace corrected to bring it in line with SAAMI specs. Hey, it's for your own safety! Based on this rule, find your situation below.

I don't reload and use only milsurp ammunition.
You shouldn't have any problems.

I don't reload but want to use commercial ammunition.
There is a potential problem with brass integrity. Commerical cases are NOT as thick as their military cousins. There is less brass, so if you use them in an original, unmeasured military chamber, there may not be sufficient material to stretch and fill the chamber without rupturing. That's bad!!

I reload.
You know that commercial brass is thinner. An easy way to see this is to weigh a fired case of each type. You'll see that the commercial case is lighter. There may not be enough brass left - after lengthening - for any decent case life. You will only aggrevate the situation by full length resizing (it weakens the case by overworking the brass), loading at or near maximum or both.
If you own a milsurp bolt gun like an Ishapore 2A or 2A1, consider neck sizing the brass for better case life, fit and accuracy.

Some Final Thoughts
Military ammunition is loaded to maximum average pressure 50,000 PSI using the modern piezo transducer method of measurement. This standard is used to ensure better consistency round to round. It is proofed at 67,000PSI. The ammunition can then be used in a wide variety of firearms with no ill effects.
Look for the NATO compatibility mark. It indicates that the cartridge is safe to use in any 7.62x51mm NATO firearm in good repair.


NATO mark found on the outside of ammunition containers and the bottom of each case rim.
Commercial ammunition has a SAAMI/ANSI maximum pressure of 62,000PSI. While not every manufacturer may load it to this level, this is the industry established maximum. This is also measured using the piezo transducer method. The proof cartridge pressure is 83,000 to 89,000 PSI. Note the differences between the military test and operational standard vs the commercial one.

The worst case scenario for shooters of 7.62 NATO rifles is as follows. Using a commercially made, maximum pressure cartridge with long headspace, fired from a weak action (ex. converted 93/95 Mausers)! The weaker action is a possible final piece of the 308 vs 7.62 NATO puzzle.
Perhaps no single element will cause your rifle to fail. Maybe you've used your rifle for a while with no ill effects. Usually a rifle will take some abuse before failing. Like a lot of things in life, Murphy's Law - If something can go wrong, it will - could very well catch up with you.
Personally, I don't like the odds.

[jrayborn]

Has anyone ever heard of a problem (kaboom, ruptured case, stinky smell, bulged brass etc.) that could either probably or possibly, be related to the use of commercial .308 used in a NATO chamber, or for that matter NATO ammo being used in a commercial chamber? Please, lets stick to only factory ammo, no handloads of any kind. And no Indian ammo, that proves nothing. It seems to me that so long as the headspace is in tolerance (near the high limit for commercial) that there really isn't much of a problem.

[W.E.G.]

.

[EMDII]

Cruffler.com credit:
http://www.cruffler.com/trivia-June01.html

Probably the best tabular data I have seen re: 'differences' and what is really 'NATO'?

[ammolab]

Good data and disscussion guys....I myself would like to see the "problem" with high pressure .308 go away. NO ONE who has a pressure gun, and a vested interest (ammo mfg. / gun mfg.) has given this a second thought, or issued a warning of any kind. Like you guys say....same bullet / same case / same velocity = same pressure. (given the normal differences that components will make in any "load" recipe).
I know army velocity is a little slower (listed at 78 feet from the muzzle, while commercial list is 'muzzle velocity')
And why worry about Army Pressure listing as PSI??? Of course it is PSI because this is a statement the average GI type will understand. I think myself it a CUP number stated as PSI for clarity. This is an ARMY Tech manual, NOT a SAMMI / Scientfic paper.

[Queenie]

Another discussion on NATO vs. Win. I have bookmarked for reference.

Fulton Armory (http://www.fulton-armory.com/308.htm)

[instr8]

So, after all this, how many grains of bullseye should I dispense when loading for my FAL?

[EMDII]

As many as it takes to get the Velocity spec'd w/o case distortion or pressure signs.
:wink:

Read the FN-manual, old chap!

[rwwje]

Originally posted by instr8
So, after all this, how many grains of bullseye should I dispense when loading for my FAL?

:rofl: :rofl: :rofl: :rofl: :rofl:

Bullseye in 7.62 = KABOOM!

[EMDII]

A Shank
C Base Diameter
D Shoulder Diameter
E Neck-1
F Neck-2/Case Mouth
G Freebore Diameter
H Pilot Diameter
K Min. Chamber Length/Base-to-Case Mouth
L Base-to-Shoulder
M Neck Length
N Freebore Length
O Rim/Belt Thickness
Q Shoulder Angle
R Throat

[EMDII]

M852 precision military chamber
Shank 0.4370
Base Diameter 0.4700
Shoulder Diameter 0.4550
Neck-1 0.3430
Neck-2/Case Mouth 0.3430
Freebore Diameter 0.3095
Pilot Diameter 0.2990
Min. Chamber Length/Base-to-Case Mouth 2.0200
Base-to-Shoulder 1.3540
Neck Length 0.3120
Freebore Length 0.0750
Rim/Belt Thickness 0.2000
Shoulder Angle 20*
Throat 1.5*

.308 Palma Match
Shank 0.4370
Base Diameter 0.4690
Shoulder Diameter 0.4550
Neck-1 0.3400
Neck-2/Case Mouth 0.3400
Freebore Diameter 0.3085
Pilot Diameter 0.2970
Min. Chamber Length/Base-to-Case Mouth 2.0200
Base-to-Shoulder 1.3540
Neck Length 0.3090
Freebore Length 0.0750
Rim/Belt Thickness 0.2000
Shoulder Angle 20*
Throat 1.5*

.308 Win commercial
Shank 0.4370
Base Diameter 0.4700
Shoulder Diameter 0.4550
Neck-1 0.3462
Neck-2/Case Mouth 0.3442
Freebore Diameter 0.3100
Pilot Diameter 0.2990
Min. Chamber Length/Base-to-Case Mouth 2.0250
Base-to-Shoulder 1.3540
Neck Length 0.3210
Freebore Length 0.0900
Rim/Belt Thickness 0.2000
Shoulder Angle 20*
Throat 1*45”

7.62 NATO
Shank 0.4670
Base Diameter 0.4725
Shoulder Diameter 0.4560
Neck-1 0.3460
Neck-2/Case Mouth 0.3460
Freebore Diameter 0.3110
Pilot Diameter 0.2990
Min. Chamber Length/Base-to-Case Mouth 2.0250
Base-to-Shoulder 1.3560
Neck Length 0.3200
Freebore Length 0.1500
Rim/Belt Thickness 0.2000
Shoulder Angle 20*
Throat 2.5*

SO- Not ALL chambers are created equal!

[instr8]

Thank You! Thank You! Thank You! EMDII, that's exactly what I needed. Refering to my other thread. You is Da Man.

[EMDII]

Thnak English Mike: he pointed it out to me.
:wink:

Clymer's site (http://www.clymertool.com/cgi-bin/reamer.cgi)

[Grouch]

MORE comparison problems, and a short explanation first.

When the military AND SAAMI cooked up their standards, there were no transducer PSI devices around (or any that were had not been proven for industrial use). There was nothing to distinguish PSI vs. PSI with, so all CUPs were converted to PSI equivalents with no explanation. There was nothing to explain. So, almost all early CUP values were published as "PSI". There was only one way to measure.

Well, one way with two variations. The military used solid brass cases in their pressure guns, but SAAMI used "drilled" cases which had the brass removed to allow direct chamber gas impingement on the pressure piston, which then drove the copper cup. So, the exact same loads in the exact same cases gave slightly different measurement values. IIRC, the military method resulted in reported chamber pressures about 2,000 "PSI" lower than the drilled case method, in theory because the case wall provided some resistance to transferring the pressure to the piston.

If your reloads using powders in the generally-accepted burn range (3031 on the fastest and whatever's next slower than 4064 on the slow side) are producing the same muzzle, 10-foot, or 78-foot velocities as the USGI or NATO-spec surplus stuff, you'll have a hard time proving to me that the load is unsafe in a 7.62 NATO barrel.

And as indicated above, remember that the US military instrumental distance for velocity was 78 feet, or 26 yards.

[torque65]

Originally posted by jrayborn
Has anyone ever heard of a problem (kaboom, ruptured case, stinky smell, bulged brass etc.) that could either probably or possibly, be related to the use of commercial .308 used in a NATO chamber, or for that matter NATO ammo being used in a commercial chamber?

Problems? I have a Remington 788 that is a wonderful gun when shooting commercial ammo, but feeding it Port NATO seems to be a REAL mistake.
Chambering doesn't give any problems, it fires fine, but the real trick is getting it OUT! You can rotate the bolt with a little effort, but to pull it back requires a good tug. Actually smacking the bolt handle forcefully with the palm was required!
I had the rifle checked out. It headspaced right in the middle of the "go" range, but the 'smith mentioned that the chamber was AT THE MINIMUM size. I could either have him run a reamer into it or leave it alone. Since it's fine with commercial ammo, I left it alone.
This one, I only shoot commercial cases through.
On another note, .308 Win cases are thrown about 18"-2' FARTHER than NATO Port cases from my STG.

What is the difference between chamber reamers between .308 Win and 7.62X51 NATO?

[English Mike]

torque65
Chamber reamer dimensions are further back in this very thread:wink:
Ted & I have the STANAG drawings for the NATO round. They're a bit blurred as to dimensions but I'm working on it!
.308 Winchester chambers ARE tighter than those for 7.62 NATO, this could be your problem.
Depends what .308 you're using in the StG. If it is a heavier bullet, or higher charge, then the brass will travel further due to higher pressures applied to the gas piston.

PS If anyone else wants the diagrams, then I can email them.

[buzz_knox]

This is a potentially stupid question, but ah well. I have an opportunity to pick up a SAR-4800 at a reasonable price. Most of the ammunition discussion concerning battle rifles has indicated that the best ammunition is the commercial .308 hollowpoints. I know there is some difference between .308 and 7.62, so I wanted to know if there would be an issue with using these hollowpoints in the SAR.

[Hebrew Battle Rifle]

Originally posted by buzz_knox
This is a potentially stupid question, but ah well. I have an opportunity to pick up a SAR-4800 at a reasonable price. Most of the ammunition discussion concerning battle rifles has indicated that the best ammunition is the commercial .308 hollowpoints. I know there is some difference between .308 and 7.62, so I wanted to know if there would be an issue with using these hollowpoints in the SAR.

There aren't any issues insofar as safety are concerned. You can use 308WIN or 7.62NATO/7.62X51mm interchangeably in your F A L.
The twist rate in a standard F A L military barrel is 1:12. This means that standerd bullets weighting between 144-168 grains will provide the best potential accuracy. Whether or not the ammo you use will be accurate in YOUR rifle can only be answered by testing in your rifle.

Also keep in mind that bullet weight alone is not the only consideration in regard to twist rate. I have 163 grain 308 bullets that will not stablize when fired through an F A L (1:12 twist rate) because they are tracer bullets. These bullets, while lighter than 168 grain, are longer than 168 gr bullets ( due to the density of the bullet materials). The longer the bullet, the tighter the twist rate has to be in order to stablize the projectile.

[PigPen]

So what is the take home message for those of us with:

1. A Browning BAR (made in Belgium) in .308

2. A Whitworth Mark X manufactured in Manchester England and imported by Interarms, in .308

3. A Springfield SAR 4800 (FN-FAL Clone) mfg. by Imbel in SA in 7.62X51

4. A Springfield Sar 48 (H&K 91 clone) mfg. by Imbel ?? in SA in 7.62X51

And a case of 762X51 from IMI in Israel.

Oh, the marvels of a world economy!!!

I have been shooting this same ammunition in all of them with "Mixed" results

PigPen

[ProGunOne]

"OK. So can we get somebody to take a few rounds of Radway Green 7.62 and run it through the copper crusher and the piezoelectric thingy?"

I'd do it but I have to get to bed. I'll be performing brain surgery in the morning. I haven't been trained to do it, but I did stay at a Holiday Inn Express. :tongue:

[win308]

My Goodness !!!!! Just start with 39 grains of H4895 and a 168 Match King. Load 5 rounds then go up 1/2 grain and load 5 more....then up 1/2 grain and 5 more....etc, etc. Write the load, in grains, on the side of each case with a Sharpie Marker.

Go to the range and shoot the 5 with the lightest load. Collect that brass. Then shoot the next 5 and save that brass. Repeat for each lot until the primers begin to crater around the firing pin hole......that is your max load for that rifle.... usually 41 grains, (but that will change a little depending on the brand of brass you use and the brand of primer).

Somewhere along the way in this experiment, you should notice the groups begin to tighten. When you find THAT best load, you really don't care if that is the absolute max or not, (though Sierra Match Kings usually do best at around full throttle in a service rifle). Settle for that.

Now you have found your most accurate load, load lots of that for match shooting. Buy the favorite ball ammo of the month for practice and you are all set to go. (If you can find any of the Australian 7.62 ball, that is about as close to match ammo as you can find these days. Buy all you can get).

After this excerise, it doesn't matter if you have a SAMMI chamber or a NATO chamber, a bolt gun or a gas gun. As long as the gun is in safe shooting condition, you should be fine.....IMHO.

[GUN SNOB]

i THOUGHT THE THICKER CASS AND LOOSER CHAMBERS WERE TO ALLOW FOR FULL AUTO HEAT AND DIRT.(opps cap lock). Since Mil. stendard is 3"+- at 100 yards thay dont need match chambers but reliability is a big plus when you might die if your wepon fails. Pushing 500-800 rpm threw a 'sporting arm' just wont happen no mater how big your mag is so why use the extra brass.

I know my L1A1 clicked shut on a 308 go gage and would swell comercial and mil. brass so bad I couldent reload it. I replaced that barrel with a Douglas and cut the chamber with a 308 reamer and i get .001 swell max. with comercial brass.

I gess the question is "has any one blowen there selfs up using factory ammo in a SERVISABLEL rifle?" DSA claims 101,100 CUP on there recivers, dont know when the bolt lug will shear or the carrier will seperate.

[shootist87122]

If you shoot milsurp 7.62x51 you don't have to pick up the brass. :) Other than that (and the price) I like .308 just fine in a FAL. Also, better quality milsurp [assuing you have a bunch in inventory] will shoot as good, or better than something like Fed American Eagle .308.

I reload too, just not for the FAL.

[English Mike]

There should be no discernable difference between brass from a .308 chamber & one cut to 7.62x51, as the spec's are within a couple of thou.

The main proviso when reloading milsurp brass is to start with a charge 10% less than for .308Win due to the smaller internal volume.

[JamesTheScot]

here's the thing...

could someone refute the information at the bottom of this thread...

http://www3.sympatico.ca/shooters/7_62vs308Pt2.htm

it clearly states that 7.62NATO has a max PSI by piezoelectric transducer method of testing of 50,000 PSI and is proofed as 67,000 PSI.

it also clearly states that .308 win has a SAAMI max (which also uses the piezoelectric transducer method of testing) of 62,000 PSI and is proofed at 83,000 to 89,000 PSI.

that is a huge difference and purports that both measures are in PSI by the piezoelectric transducer method.

so is this guy lieing? is he confused about the method of measuring the 7.62NATO loads?

i understand the CUP and transducer methods could lead to confusion, this this guy states clearly that his figures are both by transducer method.

what gives?

[ammolab]

James:

Your statement: "it clearly states that 7.62NATO has a max PSI by piezoelectric transducer method of testing of 50,000 PSI and is proofed as 67,000 PSI."

Is a misstatement...the article you link to says that the 7.62NATO has a Maximum AVERAGE pressure of 50,000psi....

as pasted and copied right here - "Military ammunition is loaded to maximum average pressure 50,000 PSI using the modern piezo transducer method of measurement."

Maximum Pressure...and Maximum Average Pressure are not interchangeable measurements or concepts.

[JamesTheScot]

fair point...but my original question remains.

is that disctinction between max pressure and max avg. pressure a distinction that really means anything? why set a max average pressure at 12,000 PSI lower than max pressure?

so then what is the max avg. pressure of .308 win?

or what is the max pressure of 7.62NATO?

does the difference in proof limits not support the use of some caution?

consider also that the author states the max avg. for NATO ammo is to ensure it operates in a wide variety of arms. but is this not even more true for commercial ammo which might find its way into a greater variety of arms than NATO spec ammo? so logic would dictate that the commercial ammo makers would set ever more conservative limits for their ammo.

the author states as an example the 7.62 conversions of 93/95 mausers...but i'm not sure if these conversions were done by NATO nations when the 7.62 NATO round was developed (Spain didn't join NATO until the 70's or 80's IIRC). but the CETME, HK's and FAL's were all pretty new on the scene at that time which would indicate to me that the 50,000 PSI average max would have been set to protect THEM, not some conversions performed by non-NATO nations.

so why would NATO limit the max average to 50,000 PSI if the max for these firearms was close to the 62,000 PSI?

at best we still have the same apples to oranges problem then. my concern is that there are many people who say .308 is OK to shoot in 7.62 chambered weapons. and i fervently hope its OK to do so. but there is still a considerable amount of ambiguity concerning how much pressure a 7.62 chambered weapon is designed to handle in repeated firings.

with all due respect, i don't see how someone can say that this issue is simply a myth.

[shootist87122]

FWIW, DSA recommends .308 in their FALs. I mostly shoot Aussie surplus in mine and based on the velocity of the Aussie round (2,840 fps), I suspect it's closer to .308 pressure (yet in a thicker militery case) than 7.62x51, but who knows (or really cares). I keep a close eye on HS and for that same reason (among others), I won't shoot commercial .308 in my Ishy 2A1 Enfield.

Common sense applies here. Do what feels right to you, but most people consider U.S. made .308 to be just fine in a quality 7.62x51 chambered firearm with good receiver and proper headspace.

[Uncle Buck]

Originally posted by JamesTheScot
here's the thing...


so is this guy lieing? is he confused about the method of measuring the 7.62NATO loads?

i understand the CUP and transducer methods could lead to confusion, this this guy states clearly that his figures are both by transducer method.

what gives?

Maybe not lying, but he is misinformed. The US military uses the copper crusher to measure pressures. Read the first part of the thread which covers this. My source for this is a US army tech manual entitled something like "Test standards for US small arms ammunition."

The most common mistake that people make is that people see "PSI" and assume that it was measured by the piezo method. All pressures are PSI regardless of how they are measured, because that is the definition of pressure. The fact that pressures can also be expressed in metric units doesn't invalidate the fact that pressures are in units of force per unit of area, because the metric units can be readily and accurately converted to US PSI.

Reloading manuals and manufaturers call this PSI pressure "CUP" to avoid just this confusion. The US army doesn't care to make this distinction because they just use the same method. That is what this whole net legend and conflict is about.

[win308]

This is turning into the "tempest in a tea pot" if I ever saw it. As long as you are not shooting "proof" rounds, crap ammo from India or 1975 CBC ammo, just shoot what you got and get on with life. If you reload, follow the instructions in the loading manual....the max loads say max for a reason.

I have shot military ball and factory commercial .308 match ammo, (US and foreign), as well as my carefully assembled reloads, in Winchester and Remington comercial bolt guns, Remington and Winchester match chambered bolt guns, standard M-1As, National Match M-1As with tighter chambers, several M-1 Garands with Douglas match .308 barrels, Imbel FALs with original factory barrels that had FAT chambers, DSA Fals with tight chambers, H&K 93s with fluted chambers, Indian Ishapor 7.62 NATO rifles (piece of junk bolt rifles), and Israeli K-98ks that were WWII German capture guns that had been rebarreled to 7.62 NATO by the Israeli military.

Out of all that, I only ever found 2 problems. 1) Federal .308 brass is soft and doesn't hold up well when you reload it....especially if you are loading for a gas gun. 2) Don't even bother to pick up the brass after shooting ammo in an Imbel barreled gun. Even with tight head speace, if you do reload it, the chamber is so radially fat, the case has streached so much upon initial firing that you get case seperations about every 4th round of reloads.

Remember, M-1A's have CAST receivers, not forged. If THEY don't blow using commercial ammo or military ammo, then any .308 gun in good shape with safe headspace will handle either GI or commercial rounds... without a problem. :eek:

Besides, the original question was, can the guy shoot hollowpoints in a Sringfield SAR 4800. The answer is yes, (but why would you want to?? That's mighty expensive ammo for shooting in a FAL).

[ammolab]

"The most common mistake that people make is that people see "PSI" and assume that it was measured by the piezo method. All pressures are PSI regardless of how they are measured, because that is the definition of pressure. The fact that pressures can also be expressed in metric units doesn't invalidate the fact that pressures are in units of force per unit of area, because the metric units can be readily and accurately converted to US PSI.

Reloading manuals and manufaturers call this PSI pressure "CUP" to avoid just this confusion. The US army doesn't care to make this distinction because they just use the same method. That is what this whole net legend and conflict is about."

I have to second this whole essay! Making a BIG deal over a difference between Old Army Tech manual pressures and current SAAMI or CIP figures is Apples to Oranges. Those old Army Figures (50,000psi) are REAL CLOSE to old Lyman reloading manuals (52,000psi) for 7.62NATO vs .308 Win. If you do not have the SAME testing methods and the SAME equipment you CAN NOT worry about these pressure differences.

Trust me...... Plenty of Ammo makers (and they all have testing equipment which we mental masturbaters do not) make both 7.62NATO and 308 Winchester ammunition of similar dimentions. If there were a significant pressure difference between the two which would create a danger and a liability problem....we would have a WARNING on every 308Win ammo box.

If you run 147gr NATO loads in the SAME pressure gun as your 150gr .308 Winchester hunting loads and you see a big pressure difference....let me know.
The ammo makers have done this, and there was no story to report.

[Uncle Buck]

I believe that the relevant tech manual for that describes the pressure test standards for US small arms ammunition is:

TM 9-1300-206 Ammunition and Explosives Standards

I was not able find a downloadable .pdf version, but photocopies can be obtained from:

www.military-info.com/MPHOTO/P110.htm

[W.E.G.]

http://www.thegunzone.com/30cal.html


http://www.falfiles.com/forums/attachment.php?s=&postid=1713680

[ammolab]

WEG: Thanks...but still different data, collected with different test methods in chambers with significant volume differences.

When someone posts ACUTAL test data of .308 Winchester vs 7.62NATO ammuntion in the SAME PRESSURE barrel we will know if any of this is significant for the shooter.

Until then it is just poorly substanciated debate.

[Uncle Buck]

Net legends are hard to kill as they multiply faster than the truth.

If you read the sources listed, the same controversy exists for the .30-06. TM-043-001-27 lists 50,000 PSI as the max for M2 ball, while the SAAMI max is 60,000 PSI for 150 g. So why don't we have a net legend warning about the extreme pressure difference for commercial .30-06?

HP white labs was comissioned by Lyman to compare the copper crusher and piezo measurements simultaneously in the same .30-06 barrel. They found that the copper gauge gave 50,000 PSI while the pizo gauge said 60,000 PSI for the same firing. They didn't fire M2 ball, but they did fire a variety of commercial ammo and reloads. The article is published in the Lyman handloading manual #47. I think you would get the same type of results with 7.62 x 51.

[Temp]

My Speer load manual states that all of their data for the .308 doesn't exceed the industry standard of 52,000 CUP,... and their listed velocities with comparative weight bullets are consistent with that which is produced by NATO spec 7.62X51 ammo.

In their lead in page which gives some background on the development of the cartridge, they state that the T65 military cartridge (7.62X51) was adopted by the military in 1954 and that Winchester introduced the T65 as the .308 Winchester in 1952. To sum up, the folks at Speer make no distinction between the two designations and their listed velocities display no difference in performance.

I'm not sure how copper units of pressure relates to psi, but according to the information presented in the manual, most modern centerfire rifle cartridges range between 46,000 and 54,000 CUP.

[klivari]

Hmm... I have been following the ".308/7.62 debate" for a while. Interesting, but I have one question: what is the max PSI rating for the barrel?

A round that is 50,000/60,000 PSI shouldn't matter if the barrel is rated for it, right?

So what is the rating for, say, an IMBEL barrel?

[Shooter-51]

I did some looking on the internet and found a few links that had to do with headspace. One references the discrepancy of pressure between SAAMI and NATO spec and says they're comparable due to the way the measurement was taken.

I lean toward the direction of the pressure being comparable. This is not because I know all the details or have any experience. It would not make any sense for NATO to develop a cartridge and then for commercial manufacturers to change it significantly. Then again, common sense is not always a good stick to measure reality.

If there is a difference in headspace, that would potentially cause more issues than a difference in pressure. A diffence in pressure would simply mean using a rifle designed to accommodate the higher of the two for compatibility with both rounds. A difference in head space, if significant, would mean incompatibility between the cartridges.

I'm not an expert in this field so I'm not making any claims, but I would like to see a little discussion on differences (or not) in headspace between .308 and NATO 7.62x51.

http://www.thegunzone.com/30cal.html

http://www.fulton-armory.com/308.htm

[ammolab]

The difference in headspace and chamber differences are because one is intended for military use....the other for sporting weapons. Military weapons demand reliability as the most important factor while sporting weapons need accuracy to be paramount.

You can have one cartridge and have differnent chamber dimentions for different uses.. I think there are 3 different .22 Long Rifle chamber dimentions used by weapon makers, "standard", "Semi-Auto", and "Match". All these different chamber specs have unique dimentions...but they are all for the same cartridge.

[Shooter-51]

Would it be a correct statement based on your comment that any ammo manufactured to .308 or 7.62x51 specifications would properly function in either .308 or 7.62x51 chambered rifles? I can understand the military being more concerned with reliability, hence the slightly more loose headspace.

Would there be any harm to adjust the headspace on a FAL to SAAMI specifications other than the possibility of reducing "functional reliability" of the rifle? Or are there other dimensions of the chamber to consider in a military rifle that would prevent a round (.308 or 7.62x51) from safely chambering and firing?

[matt78]

So what exactly is at stake when using .308 rounds in a rifle chambered in 7.62 NATO? A slightly higher risk of a catastrophe such as a chamber burst, or increased erosion to your weapon?

[shootist87122]

Originally posted by matt78
So what exactly is at stake when using .308 rounds in a rifle chambered in 7.62 NATO? A slightly higher risk of a catastrophe such as a chamber burst, or increased erosion to your weapon?

None. Zero. Zip -- just urban legend stuff. It's thinner brass is all, so HS should be correct.

[matt78]

Originally posted by shootist87122


None. Zero. Zip -- just urban legend stuff. It's thinner brass is all, so HS should be correct.

So the current severe shortage of 7.62 NATO on the market is moot, since we can still shoot the plentiful .308 rounds?

Even if these prove to be urban legends, there is just something unnerving about shooting something in my rifle that is labelled differenty than said rifle.

[ammolab]

Browning G Series FALs made by FN Belgium and imported back in the 1960s were marked."308"...HK 91s and their Clones were marked ".308"

To Major Weapon mfgs the 7.62NATO round and .308 Winchester round are the same cartridge....the internet 'experts' seem to think they know more that the people that DO have pressure barrels, and considerable risk of liability if these mfgs don't warn us of any hazard.

[brownknees]

OK I do not have either a transducer, nor a barrel that will take a copper crusher, so I have no DIRECT data on the pressure differences.
What I do have is a detailed reloading log for both .308 Win, fired in a min spec .308 chamber and similar data for 7.62 NATO fired in a NATO spec chamber that was measured as .002 over minimum, by a member here when the barrel was installed.

This was suggested earlier in the thread (working up loads in both with matching cases) and seeing how it stacked up against each other.

Now I'm using cronograph data obtained at 15 feet from the muzzle in both cases, so you'd have to use the published formula to correct back to real M/V.

.308 winchester.
(R-P cases, CCI 200 primers, 748BR powder, 165 Gr Sierra Gameking 165 Gr bullets in all cases.)

43.3 Gr= 2460FPS with a spread (ES) of 16.
45.2 gr= 2616 FPS with a spread of 44.1
41.2 Gr= 2327 FPS with a spread of 69.9.

That works out to 57.056536 FPS per grain of powder.

7.62 NATO.
(LC 68 cases, CCI 200 primers, 748BR powder, 165 Gr Sierra Gameking 165 Gr bullets in all cases.)

45.5 Gr=2638 FPS. Spread of 28
46.0 gr= 2725 FPS Spread of 13
43.3 Gr= 2450 FPS Spread of 22.7

That works out to 57.8868933 FPS per grain of powder.

Taking the difference we find that the CHANGE is 0.830357 FPS per grain.

Chamber dimensions, case thickness, and all other factors taken into concideration, and assuming that (within reasonable limits) a given powder volume change will produce a given velocity change all other things being equal we find that the SPREAD (difference between highest/lowest shot velocity in a string) is much larger than any change the case & chamber specifications.

OK so we know that 7.62 NATO is so similar to .308 Winchester in it's matching chamber that there is no real difference that is not completely obliterated by variations from shot-to-shot.

Now lets use commercial .308 Winchester in the same barrel, chamber & gun as we did with the 7.62 NATO cases.
45.5 Gr gives us 2650 FPS Spread of 20.6
47.0 Gr (near max) gives us 2780 FPS (spread opens up to 37.8)
46.0 Gr gives us 2700 FPS Spread of 21.

That works out to 58.69544 FPS per grain of powder.

OK so .308 Win has a difference with 7.62 NATO of 0.830357 FPS per grain.
When used in it's matching chamber. Whats the difference when we use .308 Win in a 7.62 chamber?

0.80864 FPS per grain.

Thats less than 1 foot per second!

Now look back at the velocity/charge figures, and the velocity spread shot-to shot in each combination. Again it's so minute that it is buried completely in the individual variations.

Based on this I'd be a heck of a lot more worried that the varying charge weights in individual rounds made with identical components, on the same machine would blow up my gun! Now I don't think any shooter is seriously concerned with every shot he makes if the next round is "overpressure", but using these numbers it seems that the difference is 20~40 times greater than any concideration about using .308 & 76.62 interchangably.

Again it's just velocity/pressure/load data, not measurments of copper crushers, or stress transducers plotting time/pressure curves, but NONE of the brass used in any of these loads, or chambers showed any signs of overpressure, nor did either rifle used to fire them. There were also zero failures to chamber, lock, extract, or eject with almost 1000 rounds being fired over several years, and with multiple makes & lots of brass.

"A difference that makes no difference is no difference." Who said that?

[shootist87122]

Uncle Buck explains where the urban legend came from quite well:

Originally posted by Uncle Buck
The point is that you get a different pressure number for .308 Winchester depending on which gauge you choose to measure it with. You get 52,000 PSI with the copper crusher gauge, which is known as copper units of pressure (cup) and you get 62,000 PSI for the same loading of the same .308 Win with the piezoelectric transducer gauge. The use of these two different gauges by the US military (copper crusher) and the commercial SAAMI specs (piezo) is responsible for the fictitious net rumor that .308 is loaded to much higher pressures (62,000) than 7.62 NATO (50,000). They are actually loaded to approximately the same pressures when you measure with the same gauge (50,000 vs 52,000 PSI). Die rumor, die!
UB

Die rumor die!

[English Mike]

Originally posted by shootist87122
Uncle Buck explains where the urban legend came from quite well:



Die rumor die!

IF I had the money, then I would like to set up two identical test barrels: One constructed to measure pressure in CUP & the other in PSI.

Run multiple loads with varying bullets/powders/primers/brass & THEN we might have a definitive destruction of the myth.

So long as headspace is within the tolerances for the round, then THERE IS NO PROBLEM.

[brownknees]

So long as headspace is within the tolerances for the round, then THERE IS NO PROBLEM.
Dead bang on, Mike.

If there were some dimensional difference THAT MATTERED, then we'd be able to buy different reloading dies for each designation of the case as no manufacturer would dare risk someone loading 7.62 in a .308 die & then getting hurt.

[Uncle Buck]

Originally posted by ENGLISH MIKE


IF I had the money, then I would like to set up two identical test barrels: One constructed to measure pressure in CUP & the other in PSI.



HP White labs did exactly this in .30-06 for the Lyman Co and the results are reported in their reloading manual #47. They had copper crusher and piezo gauges installed on the same barrel, so that they could measure the pressures simultaneously on the same firing.

I'm sure they would be willing to do this for .308 vs 7.62x51 for a reasonable sum of money.

Their motto is:
"One experiment is worth a 1000 expert opinions."

http://www.hpwhite.com/

[ammolab]

I could care less what the difference between PSI and CUP is, it just IS DIFFERENT!......I would like the SAME pressure barrel / same chamber / same bore / same measuring system (PSI or CUP fine by me) to measure ten or twenty typs of Mil spec 7.62NATO ammo and then measure ten or twenty Commercial .308 Winchester 150gr rounds.

Then we would know if .308 Win has HIGHER and DANGEROUS pressure levels than 7.62NATO ammo. Yes...HP White would be glad to do this...but it would take several thousand dollars. To rich for my blood!

But like I say. Dozens of ammo mfgs have this equipment...they make both commercial and military versions of this round....they know the pressures....and they give no warning of danger or damage from this 'phantom incompatability'.

Of course they don't issue a statement of suitability either. Why? Because when Bubba puts his muzzle into the mud and blows off the fingers of his left hand....they will have a liability problem if he was shooting a FAL and Wincheter .308 Silvertips. "Win said it was SAFE...and their .308s blew up my FAL!!!"

[ammolab]

Some more good info just surfaced in the Current Rifleman magazine about US Military pressures vs SAMMI or other commercial sources. The article is about 5.56mm vs .223 Rem ammo/pressures. Hope they write one about .308/7.62NATO soon!

Any way....they state that even when both pressures (SAMMI vs US GI) are listed with Piezeoelectric Transdusers in a PSI Scale,they cannot be used in a usefull comparison. The SAMMI pressures are measured with a transucer ported into the cartridge case while the US GI transducer is mounted with a port that is in the barrel at the mouth of the case.

What this means (for .308vs 7.62NATO pressures) is:

the SAMMI pressure will be HIGHER as it reads Maximum Chamber pressure before the bullet has even moved.

The US GI pressure will only record after the bullet has left the case and passed the transducer port at the case mouth. Since the bullet has moved quite a bit and increased the Volume for the burning powder gases...the pressure will be LOWER than that reached by the SAMMI system.

Now you know why SAMMI Pressures for .308WIN are recorded as HIGHER than US GI Army pressures for 7.62NATO when they really are the SAME. Now you know why there are no published WARNINGS about ammo interchangeability between these two rounds by anyone with a pressure barrel. Just by internet 'experts'.

[splogan]

Ok so after all this gets hashed out, If I took .308 Win and put it in a 7.62nato Enfield 2A would it work or go kaboom.

[brownknees]

Go bang, no kaboom.:rolleyes:
You probably could shoot a mixed magazine of .308 & 7.62 without ever seeing the difference in group size as compared to mixed headstamps of either.

[shootist87122]

Ishys can have loose headspace. Checking that is more important than the headstamp on the brass,

[Uncle Buck]

Originally posted by ammolab
I would like the SAME pressure barrel / same chamber / same bore / same measuring system (PSI or CUP fine by me) to measure ten or twenty typs of Mil spec 7.62NATO ammo and then measure ten or twenty Commercial .308 Winchester 150gr rounds.


http://www.smellysmleshooters.net/ammopressure.htm

Here is a guy who says he has tested thousands of military 7.62 x 51 and commercial .308 in the same pressure test gun and the 7.62 actually comes out about 5,000 PSI hotter. Go figure. Doesn't surprise me because commercial ammo manufacturers are more risk averse.

[yarro]

SAMMI max pressure spec for .308 Win when they still listed them in CUP was 52000PSI per Speer reloading manual number 11. Those measurements were of course done to SAMMI specifications that require a hole to be drilled in the case for direct impingment of the crush cylinder, which would increase the measurement by approximately 2000PSI over the military method of measuring without drilling the case. Thus 7.62 NATO and .308 Win have the same max pressure specification in CUP PSI.

As long as the bullet weight and velocity is with in the 7.62NATO specification then .308 Winchester is safe in a 7.62 NATO chambered firearm. When you get .308 Win outside of the 7.62NATO specification then all bets are off as to the proper function of your firearm. Even loads meeting the NATO specification do not guarantee function without adjusting the gas setting on your FAL as even with the same bullet and velocity the pressure curve and gas port pressure may be different between the various loadings.


-Yarro

[Uncle Buck]

In the February 2008 issue of American Rifleman, page 20 , the editors deal with the ".308 vs 7.62, what's the difference" question. They say:

"Unlike using 5.56 x 45 mm NATO ammunnition in .223-chambered guns, which the Sporting Arms and Ammunition Manufacturers Institute (SAAMI) lists in its "Unsafe Arms and Ammunition Combinations" there is no such blanket prohibition on using .308 factory ammunition in 7.62 x 51 mm rifles or visa versa"

They also state:

"Also, military 7.62 x 51 loads can be encountered that exceed SAAMI's .308 Win maximum pressure of 62,000 psi."

So here is another claim in print that 7.62 ammo may be loaded to pressures higher than .308. This is just the opposite from what you hear in the net rumor.

[blameitonfinland]

is 308 safe in an L1A1? I've used SB without issue

[ammolab]

Originally posted by blameitonfinland
is 308 safe in an L1A1? I've used SB without issue

As stated above by SAAMI and American Riflemen technical writers....the rounds are interchangeable. The use of .308 should not present you with any new safety issues at all.

[blameitonfinland]

thanks :bow:

[EricCartmanR1]

I love this thread!

[jkeen579]

I have been discussing this with a guy I work who is dead set against shooting factory 308 in 7.62 guns. He is claiming that it is the pressure put on the gas system parts due to the different powder. He is saying that the burn rate on factory is faster than military, thus, causing excessive pressure in the gas sysyem. Is there anything I can tell him that will rufute that?

[ammolab]

Originally posted by jkeen579
I have been discussing this with a guy I work who is dead set against shooting factory 308 in 7.62 guns. He is claiming that it is the pressure put on the gas system parts due to the different powder. He is saying that the burn rate on factory is faster than military, thus, causing excessive pressure in the gas sysyem. Is there anything I can tell him that will rufute that?

The powder in .308 Win ammo may well be "faster" burning than that in 7.62NATO ammo......it may well be SLOWER. Various burn rate powders are used to load 7.62NATO as well. You and I (and your friend) do not know which powder is selected to load any given lot of ammuniton.

His statement is somewhat a mistruth....as a SLOWER powder is the one which will give you a higer gas port pressure and strain the function of a semi/full auto gas powered weapon. That said...only the "Light magnum" .308 Winchester factory rounds would have a powder slow enough to cause much concern. I think these rounds have a cautionary warning on the box....maybe that is where your buddy got his 'education' on this subject.

[brownknees]

Powder burn rate tables are not to be trusted as a reference source, see any reloading manual for confirmation of that.
Also powder is a propellant, not an explosive why does this matter? Because powder burn rates vary with pressure, that's why they are called "Progressive" powders.

If he doubts that trickle a 4" long line of powder on a hard, non-flammable surface & light it. Fizz, fizz, but no BANG! then just say "Is that a fast, or slow powder?":rofl:

[Uncle Buck]

NATO has recently updated their standards for 7.62 x 51 according to NATO AC/225 (LG/3-SG/1) to EPVAT testing.

The new standard now uses a Kistler 6215 Piezoelectric Transducer gauge and has a maximum pressure of 60,190 PSI (as opposed to 50,000 PSI CUP).

http://en.wikipedia.org/wiki/NATO_EPVAT_testing

This is much more comparable to the SAAMI and CIP pressure specs. The ammunition hasn't changed, just the type of gauge and the pressure specs. Now you can compare apples to apples.

UB

[JamesTheScot]

So why any difference at all between x51 and .308 using the piezo transducer?

The old x51 CUP figure was less than the SAAMI .308 CUP figure ostensibly due to the different locations and methods of mounting the copper crusher to the chamber.

So is there a difference then in how NATO attaches the piezo transducer versus how SAAMI does it? I know that 1,810 PSI isn't much, but the fact that there is a difference still makes one wonder a little bit if NATO rifles are not as strong as .308 rifles. Sometimes, the devil is in the cumulative wear on parts, not just in a sudden catastrophic failure.

I'm a convert and think it's OK to shoot .308 in a good x51 chamber, but it's still a little disconcerting that no one in the ammo industry seems to be willing to take a stand. I suspect that there's some uncertainty there as well and they aren't comfortable endorsing the use of their ammo in milsurp rifles.

I'm starting to look at this more like the +P issue with .38's. Some modest use of .308 is OK but a steady diet might loosen things up a bit?

Thoughts?

[brownknees]

After a couple of thousand rounds of both I'm finding no appreciable wear.:beer:

[Uncle Buck]

Originally posted by JamesTheScot
So why any difference at all between x51 and .308 using the piezo transducer?


It could be a number of things:

1. A real difference, but still not a very significant one.

2. A definition difference. Some use maximum pressure for individual cartridges, while others use a "maximum average pressure", where the maximum is averaged over a number of individual measurements, some of which are above and below the average.

3. Gauge difference. NATO uses the same gauge and measurement methods as the European CIP standard and the pressure maximums are exactly the same for NATO and .308 CIP.

The apparent difference between NATO and SAAMI (approx 2%) is not of the same magnitude as the difference between +P and standard pistol ammo which is more like 10%.

[lazersnthjungle]

However complex, I'd have to side with the fact that the pressures are "essentially" the same. The greater issue still may be the headspace. Do you suppose a visual inspection of a commercial .308 Win case from a 7.62 chamber would reveal any distortion or other signs of distress?

[brownknees]

Not with any of the 1,000s I've fired.
Visually you won't see a darned thing, the difference is way to small to be visually aparrent. I've used the Stoney point gage with a caliper & can't find diddly either.
In reality the chambering & extraction process is violent enough to hide the thoeretical differences between the two as the stretching & re-headspacing on chambering is bigger than the difference!

[lazersnthjungle]

Soo . . . I'm thinking the Comm. .308 cases just won't stand up to the reloading as well . . .(?)

I've been casting about on the +P .38 analogy since I often carry a snubby and have (probably) overshot it too many times with +P.

Best I can figure, the pressure differences we're seeing with .308 and 7.62 may be 3% (at most). But +P .38 is at least 10-12% over MAXIMUM pressures. It is more like 60% over standard pressures.

The +P .38 thing is admittedly off-topic, but since the analogy was cited, I think it fair to level the playing field.

The difference between .308 Win and 7.62x51 pressures are minuscule compared to standard .38 special and +P.

[brownknees]

Soo . . . I'm thinking the Comm. .308 cases just won't stand up to the reloading as well . . .(?)
In something like a FAL the cycling process beats up the brass so much that's the limiting factor for either case. When I reloaded both for a bolt action I could get 10~12 loads out of either. It seems to be a question of itty-bitty differences in headspace, once you've resized once to the "correct" headspace the wear is limited so there isn't much difference really.

Which bring on the thought that if this made a real difference you'd be able to buy either 7.62, or .308 Win. dies, & for some reason you can't:uhoh: maybe another indication of the difference being thoeretical only.:wink:

[lazersnthjungle]

Good point on the dies!

I don't guess my M1A would beat up brass any more or less than an FAL (?)

[brownknees]

More like differently:smile:
My M1a put a diagonal mark on rounds 1 thru 19, it didn't look as bad as the creased necks of the FAL, but it did shorten case life. ON the bright side round 20 was cherry:rofl: