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Old January 13, 2004, 00:33   #51
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So, after all this, how many grains of bullseye should I dispense when loading for my FAL?
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Old January 13, 2004, 10:26   #52
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As many as it takes to get the Velocity spec'd w/o case distortion or pressure signs.


Read the FN-manual, old chap!
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Old January 14, 2004, 10:06   #53
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Quote:
Originally posted by instr8
So, after all this, how many grains of bullseye should I dispense when loading for my FAL?


Bullseye in 7.62 = KABOOM!
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Old January 18, 2004, 08:15   #54
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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
Attached Images
File Type: jpg chamber dimensions.jpg (20.7 KB, 1424 views)
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Old January 18, 2004, 08:28   #55
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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!
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Old January 18, 2004, 10:39   #56
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Thank You! Thank You! Thank You! EMDII, that's exactly what I needed. Refering to my other thread. You is Da Man.
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Old January 18, 2004, 15:52   #57
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Thnak English Mike: he pointed it out to me.


Clymer's site
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Old April 26, 2004, 11:25   #58
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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.
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Old April 26, 2004, 13:13   #59
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Quote:
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?
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Old April 26, 2004, 19:14   #60
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torque65
Chamber reamer dimensions are further back in this very thread
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.
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Old July 07, 2004, 15:21   #61
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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.
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Old July 07, 2004, 15:38   #62
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Quote:
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.
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Old July 25, 2004, 13:14   #63
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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

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Old December 03, 2004, 23:45   #64
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"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.
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Old May 19, 2005, 13:41   #65
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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.
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Old June 23, 2006, 23:01   #66
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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.
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Old June 23, 2006, 23:20   #67
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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.
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Old June 26, 2006, 18:19   #68
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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.
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Old October 18, 2006, 16:10   #69
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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?
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Old October 18, 2006, 18:21   #70
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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.
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Old October 19, 2006, 13:20   #71
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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.
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Old October 19, 2006, 14:00   #72
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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.
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Old October 19, 2006, 18:41   #73
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Quote:
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.
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Old October 19, 2006, 20:39   #74
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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.

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).
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Old October 19, 2006, 21:51   #75
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"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.
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Old October 21, 2006, 15:10   #76
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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
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Old October 30, 2006, 10:11   #77
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Old October 30, 2006, 11:01   #78
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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.
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Old October 31, 2006, 12:13   #79
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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.
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Old October 31, 2006, 13:00   #80
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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.
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Old November 26, 2006, 03:00   #81
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Exclamation

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?
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Old February 04, 2007, 01:02   #82
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Question Is there a difference with headspace?

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

Last edited by Shooter-51; February 04, 2007 at 01:08.
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Old February 04, 2007, 23:47   #83
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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.
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Old February 07, 2007, 00:24   #84
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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?
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Old May 05, 2007, 00:39   #85
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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?
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Old May 05, 2007, 08:27   #86
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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.
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Old May 05, 2007, 10:05   #87
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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.
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Old May 05, 2007, 17:40   #88
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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.
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Old May 05, 2007, 18:24   #89
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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?

Last edited by brownknees; May 05, 2007 at 20:50.
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Old May 05, 2007, 18:48   #90
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Uncle Buck explains where the urban legend came from quite well:

Quote:
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!
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Old May 05, 2007, 19:48   #91
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Quote:
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.
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Old May 05, 2007, 20:44   #92
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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.
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Old May 12, 2007, 19:22   #93
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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/
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Old May 12, 2007, 21:16   #94
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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!!!"
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Old August 28, 2007, 22:49   #95
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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'.
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Old October 20, 2007, 18:42   #96
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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.
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Old October 20, 2007, 20:25   #97
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Go bang, no kaboom.
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.
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Old October 20, 2007, 22:15   #98
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Ishys can have loose headspace. Checking that is more important than the headstamp on the brass,
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Old December 09, 2007, 21:43   #99
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Quote:
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.
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Old January 09, 2008, 21:04   #100
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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.


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