Dr. Gary Roberts and the .308 round

[mparrish]

I just got back from a firearms instructor's conference in which Dr. Gary Roberts was a guest speaker. Topics covered all the angles and did address the on going .223 versus .308 debate. Essentially, Dr. Roberts touted the .223 as an appropriate round for Northern peoples of average height and build. However, he stated clearly that the .308 was a better round all round for current conflicts. However, he did go into discussion of a new load that even DSA has gotten into the act for in building a test rifle. Its a 6.8mm round with some impressive ballistics, low barrel wear, flat trajectory and better penetration. I'll pull up the specs when I find my notes.

Back to the .308: he emphasized that the .308 was providing better performance on creating both permanant and temporary cavaities with greater expansion at shorter distances in the human body. The discussion focused on the fact that US and allied troops have been fighting people with thinner bodies that .223 will penetrate through but not expand until after exit (looking at an average of 7-8 inches of chest depth versus an average US person (male, non obese) of 12-14 inches. With current .223 rounds expanding at from 8 inches on, there is a problem. He was showing that even 7.62 NATO ball was becomming effective in five inches or even less, once you went to ballistic tipped or JSP rounds. He emphasized that many black and green military units were carrying .308 capable rifles again.

Of course, being the FAL fanatic I am, I was grinning just a bit.

If you get a chance to meet or speak with Dr. Roberts, its a rapid fire treat. I didn't agree with everything he said but he makes excellent sense overall.

[Bruce Allen]

Cool.

It is just amazing to see how the "experts" bs'ed there way into selling the smaller is better theory to the military while at the same time being absolutely unable to sway the hunting community that a .223 is anything more than a varmit round.

From everything I have read the only reason the M4 and clones have been effective in combat so far is superior accuracy and marksmenship of the Amercian soldier.

[Eclipse]

Good article with info on the new 6.8 round. Also looks at other calibers to replace 5.56mm in the M16 platform

http://www.angelfire.com/art/enchanter/bullet.html#68

[mparrish]

Eclipse,

Yes! That's the information the good doctor was rattling off. Again, what perked my ears up was that he mentioned DSA as a competiting builder. It makes sense with DSA, who has already experimented with other loads.

[yovinny]

Originally posted by Bruce Allen
Cool.

It is just amazing to see how the "experts" bs'ed there way into selling the smaller is better theory to the military while at the same time being absolutely unable to sway the hunting community that a .223 is anything more than a varmit round.

From everything I have read the only reason the M4 and clones have been effective in combat so far is superior accuracy and marksmenship of the Amercian soldier.

No flame; but it was also members of the military that touted for the smaller high velocity round. I cant remember his name but the guy at Aberdeen who did all the shooting tests on animals and cadavers pushed hard for it along with MANY others in the military hierarchy that should have known better. To say nothing about the political aspect of it. Dont forget, they went to a privately held company for the new M-16, LOTS of money changed hands. YOOOO Vinny

[CS273]

I don't think from all the situation reports I've heard about in the middle east had anything to do with the size of a person's body.

Most have determined that the failure was mainly due to the lack of velocity of the bullet upon impact. This has been mainly linked to the fact that the ammunition has been fired from rifles with 14.5 inch barrels. Most ammunition fired from 20" barrels had adequate terminal ballistics. That also applies to ammunition fired from M249 SAWs (Squad Automatic Weapons).

I find it weird that he is the only one that comes to the conclusion about body dimensions versus lack of velocity upon impact. That's not the approach that the US Military is working when it comes to improvements.

Also, military FMJ ammunition doesn't expand. It fragments because it isn't softpoint ammunition. The base of the bullet is heavier than the tip. Since the tip isn't expanding and moving the center of gravity to the base, the base will start to over take the tip and flip end over end in the body. The structural instablity in the jacket of the bullet will fragment.

That fragmentation is where military ammunition gets it's ability to cause wounds. It happens very quickly inside of a body. I think his focus is on law enforcement engagements with softpoint ammunition. Either that or his conclusion seem really weird. Or I'm weird or Both....

[mparrish]

Let's go back to the .223. It was designed for the USAF replacement for the air police and their M1 carbines. In that role, it is excellent. As for other services adopting it, that has been beaten and argued to death.

As for what Dr. Roberts has stated, body size was only one factor, not the only one. However, take the round, the unfortunate overpenetration that was occurring in thinner torsoed persons, firing from a rifle with what is an effective range of approximately 300 yards (+/-) (M4 or GAU/GUU5P) and it spelled trouble. What Dr. Roberts was pointing out was that the 5.56/.223 is a varmint round with good attributes in use against northern tier sized persons. However, tack on an obese subject or a subject who's torso is thinner than the expansion of a .223 round, and that has spelled trouble for troops fighting in current conflicts.

Again, he stated that the .308 was expending energy faster upon entry into a body.

As for military improvements, my years in the military including USAF CATM showed that improvements in the actual round was only occurring when needs arose. The 6.8mm program was not started by any echelons above reality. It was started by a group of NCOs who thought correctly that they could fine a better round that fit the .223 attributes and the 7.62 NATO qualities.

His conversation again confirmed the .308 as a quality round that was seeing increased use again in the military after real failures to stop in the field.

Dr. Gary Roberts, DDS - presently serving in the USNR, former police officer in the bay area, worked with Dr. Fackler on refining ballistic studies, working at Standford. A Google search will show lots on him. He is also a moderator at the Terminal Effects forum at www.tacticalforums.com. Nice but blunt fellow to talk to and a huge wealth of information. In that same meeting, there were reps from Federal and Hornady. He didn't mince words even though they were there. The Federal reps winced on occasion when he said a Federal round "flat out sucked." Hornday was also taken to task for a 55 gn load that was poor on human targets.

[CS273]

Here's a link to the ammo oracle, it's always good to post this link once in a while.

http://www.ammo-oracle.com/

[W.E.G.]

Those M16's are junk...junk...junk.

Now, I say they need to cut all the receivers in two, and sell the leftover "junk-parts" to me.

[Sgt_Gold]

What concerns me most about Dr. Roberts data is he is using the term 'expansion'. Military FMJ gets it's terminal ballistics from fragmentation, not expantion. I usually don't play barracks lawyer, but a recognized professional in the field of wound ballistics should get the terminology straight.

The information about having problems with 'thinner' enemy soldiers is on target. All FMJ rounds need specific penetration depths to fragment properly. If there isn't enough mass, the bullet will exit the target without fragmenting. A cross torso shot will almost always result in good terminal ballistics, but a through the arm or leg will leave a puncture wound and not much else.

Some of Roberts information appears to be in contract to Facklers. I would suggest the following reading:

www.ammo-oracle.com
http://www.btammolabs.com/fackler/wo...ary_rifles.pdf

The 'real' would information is going to come from battlefield autopsy results, not gello or computer simulations.

[Bruce Allen]

Originally posted by Sgt_Gold
..... The 'real' would information is going to come from battlefield autopsy results, not gello or computer simulations.

Exactly.
I am sure that data exists but what I am not sure about is the willingness of the organizations - military and otherwise - to pursue a meaningful investigation.
A true scientific inquiry where data is gathered and compiled and then let the chips fall where they may, instead of gathering info to support one theory or another.

Like the Hatcher tests for the .45 years ago.
Even cadavers were shot and then analyzed.

Personally I feel the Russians are on the right track, and the original FAL designers. Wasn't the round a .280, which about 7mm?? I personally think that would be ideal at about 2200-2500fps.

[Sgt_Gold]

Originally posted by Bruce Allen


Personally I feel the Russians are on the right track, and the original FAL designers. Wasn't the round a .280, which about 7mm?? I personally think that would be ideal at about 2200-2500fps.

The interesting thing was the original caliber of the M-1 Garand was something like .28 caliber. None other than Genartal MacArthur decided that since the Army had gazillions of 30.06 rounds, the M-1 was going to be a 30.06 rifle.

[Eclipse]

It appears many of the problems with the M16 are a combination of:

1) Switch from M16 20" to M4 14.5" barrels
2) Change from the old M193 55 grain round to the 62 grain SS109 (M855) round.

I've read reports about how the 55 gr ammo breaks apart when hitting bone - from a combat medics perspective apparently the round does tremendous damage to the body. Village Voice article dealing with Israeli use of 55 grain 5.56 ammo in the early days of the 2nd Palestinian uprising.

Shoot to Maim by Lamis Andoni & Sandy Tolan
Israel's Favored Ammo is Crippling a Generation of Young Palestinians
http://www.villagevoice.com/issues/0108/tolan.php

"The high rates of crippling injuries are in large part due to the fragmenting bullets fired by M16s. The American-made Colt weapons, introduced during the Vietnam War as lightweight field rifles capable of inflicting maximum damage on the enemy, are being used increasingly by the Israel Defense Forces against civilian demonstrators. The M16 ammunition often breaks into tiny pieces after penetration, ripping up muscle and nerve and causing multiple internal injuries, much like those of the internationally banned dumdum bullets.

Forensics experts in the United States and Europe, who agreed for this article to examine the X rays of Fouad Mahed and other wounded Palestinians, confirm repeated casualties from M16s, shotguns, and other live ammunition. These images, together with other X rays seen in West Bank and Jordanian hospitals, show a pattern some forensics specialists call a "lead snowstorm," the fragmentation of high-velocity military ammunition, fired at civilians. Many of the wounded were hit at short range—less than 100 meters—compounding internal damage."

[Eclipse]

Another researcher to read is Martin L. Fackler

Military rifle bullet wound patterns
http://home.snafu.de/l.moeller/milit..._patterns.html

Article compares 5.56, 7.62 Nato, 7.62x39 performance in ballistic jello

[Sgt_Gold]

Originally posted by Eclipse
It appears many of the problems with the M16 are a combination of:

1) Switch from M16 20" to M4 14.5" barrels
2) Change from the old M193 55 grain round to the 62 grain SS109 (M855) round.

I've read reports about how the 55 gr ammo breaks apart when hitting bone - from a combat medics perspective apparently the round does tremendous damage to the body. Village Voice article dealing with Israeli use of 55 grain 5.56 ammo in the early days of the 2nd Palestinian uprising.

The 62 gr round fragments just as well as the 55 gr round. The problem is that the 14.5 inch barrel means that you need to keep the range down to less than 150 meters if you're using an M-4. There have been almost no complaints from the M-16's and M-249's.

The article inthe Vilage Voice was almost as bad as the liberal press can get. I live in NYC and am familiar with the slant of the Voice on a regular basis. Added to the 'objective' slant of the article is the fact that it was written under the supervision of the UC Berkley. Hardly an objective popint of view.

[Bearwhositshere]

I wonder what kind of results you would get from a Krinkov in 5.45x39 against Skinnies? What is difficult to pin down is every variable in every test.
I think Jeff cooper said it best "there is no substitue for good bullet placement"

Personally I have seen people drop and die from .38s and 9mms and people walk away from hits from a .45 I really don't know if you will ever find the "silver bullet" or "golden bb" of milspec ammo. But I do know that practice makes perfect.

Of course having said all that I'd rather have a .308

[Gremper]

Barrel length is only part of the problem. The first M-16 rifles shipped to Vietnam (actually, full automatic variants of the AR-15) had a 1-14" rifling rate. Terminal ballistics were devastating (at a slight cost in accuracy). The M-16 that the military adopted had, for better accuracy, 1-9" rifling. In order to stabilize the newer NATO rounds the current M-4 (basically an upgraded Vietnam era CAR-15) has a 1-7" rifling rate. The bullet is overstabilized and refuses to tumble within the required distance.

[Bubba FAL]

Nothin new under the sun... During the pig and cadaver tests performed at Aberdeen, some of the most devastating wounds were created by the old 6.5 Carcano round. Seems the base-heavy, aluminum tipped projectile design resulted in rapid destabilization upon contact with soft tissue.

[mparrish]

Since we broach the issue of handgun rounds, one thing Dr. Roberts said (apparently he works trauma in the bay area so he sees lots of real world issues, x-rays of shot subjects, etc.) was that research is showing a 90% survivability rate for those shot with handgun rounds. Much of this is from the fact that we have the capability to get critical care to subjects faster than ever before and advances in reconstruction of tissues and muscle masses. Also, the human body can be shot in many places without killing a subject. One photo he showed was of a marine who had his jaw and lower face exploded out due to an errant round. The marine was conscious, alert and aware. He survived. The picture was pretty, well, amazing to see. Creapy to see the marine stare at the camera with clear eyes. This survivability rate corresponds what I researched. Since our society gets all wrapped around the axle about those killed by firearms, I would suggest a better indicator of crime up or down is the number of "good" shootings (lethal or survivable). That paints a better picture of the true crime rate versus how many get whacked these days (as an example, the UCRs for the Clinton era showed a decrease of deaths from gunfire. However, assaults on the whole with firearms stayed nearly the same and assaults with other weapons did increase slightly).

Again, back to the topic. I think that with recent failures of the 5.56 in certain environments, I can truely see the military looking hard at adopting the 6.8 or equivalent in a 18 inch barrel platform. I see the days of 14.5 inch barrels being phased out, particularly if you see the individual services adopt the rifle that suits them best (i.e., the USMC deciding to keep the A4 version of the M16 versus jumping on the bandwagon and adopting the M4 or varient).

I can see an AR-10 style rifle being configured to the new round to facilitate ease of conversion training, use of a collapsible stock or fixed, and ease of parts removal. Of course, a FAL could fit almost all of that excluding the collapsible stock.

[kfox]

The July 21st issue of Army Times contains the info on the next battle rifle. The military will begin converting to the XM8 (5.56mm) in two years, followed a few years later by the XM29. Buck Rogers rides again.

[yovinny]

I can't help but think that they keep trying to re-invent the wheel. If they had used the M-16a1 as it was and never went to the a2 or the heavy bullet or faster twist (for NATO) they wouldent keep having problems. In otherwords; it's a damn CARBINE, use it as such within those limitations. If they want or need a RIFLE, they already had one of the best, the M-14.

[elbo]

Originally posted by Gremper
has a 1-7" rifling rate. The bullet is overstabilized and refuses to tumble within the required distance.

IIRC 1in7 was to enhance fragmentation, giving it a rotational velocity at which the slight upset of the jacket will cause it to come apart. The new rounds are ment to fragment not tumble. Is that correct?

[Sgt_Gold]

Originally posted by Gremper
Barrel length is only part of the problem. The first M-16 rifles shipped to Vietnam (actually, full automatic variants of the AR-15) had a 1-14" rifling rate. Terminal ballistics were devastating (at a slight cost in accuracy). The M-16 that the military adopted had, for better accuracy, 1-9" rifling. In order to stabilize the newer NATO rounds the current M-4 (basically an upgraded Vietnam era CAR-15) has a 1-7" rifling rate. The bullet is overstabilized and refuses to tumble within the required distance.

There is so much wrong here I almost don't know where to start. The military went to a 1-12" twist for the M-16A1. The M-16A2 has a 1-7" twist. The 1-9" twist is on civilian rifles only, it was NEVER adopted by the military. The 1-7" twist has absoutly NOTHING to do with fragmentation, and EVERYTHING to do with stabilizing the tracer round. The tracer is much heavier than the standard SS109 round and won't shoot straight out of a slower twist. Military FMJ dosen't tumble, it fragments. M193 will fragment quite well through the 1-7" barrel although it was designed for the slower 1-12" twist.

For all the info you need, check:

www.ammo-oracle.com

[mparrish]

How'd we wander over to the 223 folks? Ok, back to what the FAL fires, the .308. Found my notes . . .

Title of the discussion was "Wound Ballistics." Best .308 Dr. Roberts has tested to date (unknown from what platform though, I'll e-mail him to find out) was the 155 gn AMAX or 155 gn Hornady TAP.

His e-mail, if you wish to hash out any questions is gkrdds@aol.com. His address is: Gary K. Roberts, DDS, Stanford University Medical Center, 750 Welch Rd, Room 118, Palo Alto, CA 94304.

[CS273]

Discussing softpoint bullets once again reinforces my contention that he's not talking about military conflicts. Softpoint ammunition is banned by the Hague Convention, which doesn't apply when dealing with terrorists though.

I repeat that FMJ bullets won't fragment in a human body whether the body is one inch thick or one hundred feet thick if the bullet enters the body with insufficient velocity. There are basic laws of physics involved here.

In order to overcome the structure stability of the bullet there must be sufficient exterior forces on the bullet to cause fragmentation. If the velocity drops below a certain point for a particular bullet design or construction it won't fragment. Not to be sarcastic, but take a FMJ bullet and drop it on your arm, it doesn't fragment, why not? Not enough velocity.

This information has been analyzed and presented in many papers by Dr. Fackler. I doubt that anyone will come up with any theory which will disprove fundamental laws of physics concerning bullet expansion or fragmentation. All other information is just anecdoctal information, which is very useful, but not necessarily relevant. The reason I say that is because military and law enforcement personnel have legal rulings with which to guide their selection of calibers and bullets. Future legal case also prevent utilization of whatever caliber/bullet they may wish to use.

[Gremper]

Sgt_Gold
You are probably correct about the 1-12" vs 1-9" twist on the M-16. I know the rifling rate was changed from 1-14" to enhance accuracy. I spent most of my tour in Vietnam in AirEvac and saw plenty of wound X Rays. What you are referring to as fragmentation is, to the best of my recollection, the bullet breaking in half at the cannelure AFTER it loses stability and tumbles. I do not recall any instances of true fragmentation, even after the projectile hit bone. I believe that the faster rotation from a 1-7" barrel will cause the still stable bullet to punch through flesh with more of an ice-pick type wound. I am not a doctor or a ballistician but I damn well know what I saw on the X Ray film that went with our patients!

[Bubba FAL]

I don't claim to be an expert but from ballistic studies I've read, the 5.56 projectile will typically yaw twice, then turn over base first to come apart at the cannelure (fragment). Assuming sufficient tissue mass to allow the above to occur.

The air pocket in the russki 5.45 projectile facilitates the tumbling process by allowing the core to shift upon impact with tissue. The Muj reported particularly nasty wounds from the 5.45 during their engagements with the Soviets back in the '80s. (They quickly learned to engage the Soviets from outside effective AK range as a result.)

7.62NATO FMJ projectiles typically result in a through & through wound as they require more tissue (mass) to complete the destabilization process (affect bullet momentum). OTOH, the 7.62N uses that momentum to punch through small trees and strike targets taking cover behind same. Always a trade off in physics.

Firing a 62gr. steel core projectile at a reduced velocity ala the M4 does have a negative affect on the wound ballistics of the round. Especially if, as found in Somalia and Afghanistan, the target has a less massive torso. Just not enough time to tumble and expend the energy. Reports from Iraq indicate improved performance of the SS109 ammo due to the generally heavier torso of the average Iraqi soldier.

There are many other factors in play when it comes to wound ballistics (like the Somali propensity for Khat - a mild narcotic) and any solution will involve a compromise, but it would seem that something in the 6-7mm range would be worth investigating.

Just my .02, take it for what it's worth...

[mparrish]

Bubba:

Spot on! In fact, I remember Dr. Roberts discussing the 5.45 round and the hollow cavity. Best explanation I've heard so far. Keep it coming!

[CS273]

Here are several quotes from the people at Lost River Ballistics. I provide this information mainly to let people know certain aspects about ballistics, such as stabilization, etc.

The site is located at:
http://www.lostriverballistic.com/LRB_Start.htm

Read the article entitled, "The importance of twist".

"In order to overcome the inherent wobble in a bullet, rifling was put into the barrel of firearms and twist was introduced as a means to stabilize the bullet. Twist works by gyroscopic stability produced by rotational momentum of a spinning object. For example, a spinning a top becomes more stable the faster it spins until it loses stability. The same is true for a bullet; as spin rates increase, so does the stability of the projectile. "

"The wobble created at high twist rates is from inconsistencies in the shape and sectional density of the bullet. For example, a small discrepancy in weight distribution through the bullet is accentuated as the bullet is spun at very high rpm’s. This is apparent down range as a bullets rotational momentum causes the bullets weight discrepancies to exacerbate the wobble inherent in every bullet. These discrepancies are like putting a lead weight in a volleyball and then rolling it across the floor. When the ball is rolled fast across the floor, the inconsistency in the weight of the ball is much more apparent. This is analogous to rotational momentum of a bullet. If there are inconsistencies within the form of the bullet, these inconsistencies will be accentuated as the twist rate of the bullet is increased. The problem with stability is not the rate of spin; rather it is a problem of bullet manufacturing. Using more than one material in the production of a bullet causes weight inconsistencies to intensify exponentially, and this makes it virtually impossible to increase twist rates without ruining the trajectory of a bullet. As a result of ballistically inferior design in the manufacturing of bullets, many shooters have gone to slower twist rates in their rifles to prevent wobble. This is not the answer to better stabilization. "

" As a bullet is streamlined it presents many problems with respect to stability. One of these problems is its tendency to swap ends. As the bullet flies, air tends to get up under the bullet causing it to tumble. This effect can be overcome by spinning the bullet. But unless the spin rate is very high, the bullet will wobble downrange defeating the purpose of an aerodynamic bullet. This presents another problem in that as the bullet is spun at high twist rates it wobbles due to discrepancies in weight distribution. Yet another problem with high twist rates is creating a bullet that can withstand the intense force put on it by the high rotational momentum. Most jacketed bullets will fall apart at high velocities and high twist rates. So what needs to be accomplished is a highly streamlined bullet that will not wobble at high twist rates, will hold together, and retain its twist downrange to stabilize the bullet through the transonic speed range "

As mentioned by others, ballistics involve many aspects. I don't know them all, nor do I have a desire to learn them all. It's interesting to read what the experts know. It's also amazing as we understand more from the real experts is how little we really know, myself included. There has been much hype and misinformation for many years about terminal ballistics in phone books, gellatin, etc. It's different in the human body because of many aspects, such as bone, organs, blood, etc.

The topics are very interesting, but I doubt any one expert knows all aspects and I don't claim to be an expert. Interesting information guys keep adding more thoughts.

One other tidbit, the human body is approximately 100 times more dense than air. Bullets need much great twist rates to maintain stability in a denser medium. They actually lose stability when entering bodies, which is why the tumble. That mainly applies to FMJ bullets.

[elbo]

Originally posted by CS273


I repeat that FMJ bullets won't fragment in a human body whether the body is one inch thick or one hundred feet thick if the bullet enters the body with insufficient velocity. There are basic laws of physics involved here.

In order to overcome the structure stability of the bullet there must be sufficient exterior forces on the bullet to cause fragmentation. If the velocity drops below a certain point for a particular bullet design or construction it won't fragment. Not to be sarcastic, but take a FMJ bullet and drop it on your arm, it doesn't fragment, why not? Not enough velocity.

Spin it at 300,000 RPM and drop it on your arm.

[CS273]

I'm not exactly sure what the RPM's are for 55 gr. FMJBT bullets when they come out of a 1 in 7" twist barrel, but they are very high.

I'm not sure that the bullet would fragment with just rotational momentum. It might be an interesting experiment. Go head and give it a try and report back the results

I'm sure it probably won't do your arm much good though

As Lost River Ballistics points out bullets can fly apart from high RPM's due to their poor structure.

Yes, I did realize you were joking.......

[lutefisk]

I think Sgt Gold is correct about the 1:7 to stabilize the heavier and longer tracer rds. I also recall that the 5.56 actually outperformed the 7.62 at extended ranges on penetration tests-helmets. I remember that one variable on wound ballistics studies involved "standardized" surgical proceedures-thus, the length of bowel removed from a 7.62 X 39 might be the same as that from a 5.56 even though the wounds were way different. I loaned the book out and never got it back. Think it was called "Secondary Wound Ballistics" or something like that. Color of book was red. The data was primarily from Vietnam.

[Sgt_Gold]

Originally posted by Bubba FAL
7.62NATO FMJ projectiles typically result in a through & through wound as they require more tissue (mass) to complete the destabilization process (affect bullet momentum). OTOH, the 7.62N uses that momentum to punch through small trees and strike targets taking cover behind same. Always a trade off in physics.

Firing a 62gr. steel core projectile at a reduced velocity ala the M4 does have a negative affect on the wound ballistics of the round. Especially if, as found in Somalia and Afghanistan, the target has a less massive torso. Just not enough time to tumble and expend the energy. Reports from Iraq indicate improved performance of the SS109 ammo due to the generally heavier torso of the average Iraqi soldier.

There are many other factors in play when it comes to wound ballistics (like the Somali propensity for Khat - a mild narcotic) and any solution will involve a compromise, but it would seem that something in the 6-7mm range would be worth investigating.

Just my .02, take it for what it's worth... [/B]

Good info here. It's important to remember that military ammo is designed to produce acceptable accuracy in the weapon it's used in, and in some cases numerous weapons use the sam ammo. The ammo is also designed to function the weapon in all climates. Skinny Somali's and you average Iraqi are two completly different targets in terms of cross section.

Twist rate also has an effect on terminal ballistics. Inertia comes into play when you compare the original 1-14 to the current 1-7 twist rates. The slower the twist, the quicker the bullet will begin to destabilize once it enters the body. Bullet construction is also a factor. In 5.56, bullets weighing less than 50gr can and do shed their jackets when fired through a 1-7 barrel. All ballistics is a compromise, the 'best' round for one thing works poorly in another.

[Bruce Allen]

Originally posted by lutefisk
I think Sgt Gold is correct about the 1:7 to stabilize the heavier and longer tracer rds. I also recall that the 5.56 actually outperformed the 7.62 at extended ranges on penetration tests-helmets.....

I think that is wrong..
The 55 grn fmj bullet would not penetrate a helmet past 200 or 220 yards so development requests went out and the 62 grn penetrator round was developed by FN (if I recall correctly) and adopted by US military.
The M16A1 with the 1-12" twist could not stabilize that bullet nor the tracer and the 1-7 twist barrels were adopted. Wasn't that the A2?

(cut and pasted):
Background Information
on the
UNITED STATES RIFLE
CALIBER 5.56mm
M16


The next major design change made to the M16/M16A1 family occurred after a series of NATO-sponsored tests were conducted to determine what type of ammunition would be needed after 1980. During these tests conducted between April, 1977 and the Spring of 1979, most of the cartridges submitted by NATO member nations used the standard 5.56mm M193 Ball round of the M16 as a starting point, but the West German introduced a 4.7mm caseless ammunition. After the testing was completed, the Belgian SS109 round was selected as the second NATO cartridge.28 The SS109 round used a projectile with a combination steel-and-lead core fired with a muzzle velocity of 3000 feet per second. It performed significantly better the American M193 round, but this performance required a rifling twist of 1 turn in 7 inches, as compared to the M16/M16A1's rifling twist of 1 turn in 12 inches. When fired in rifles using the rifling twist of 1 turn in 12 inches, the SS109 round was only marginally better than the M193 round. With this, the American military decided to convert to the faster rifling twist and correct some deficiencies in the M16/M16A1 as well.29 The new design included the following design changes:


Barrel with a rifling twist of 1:7 and with a heavier diameter near the muzzle.
Stronger, more durable, more ergonomic buttstock.
Handguards now used an interchangeable top-and-bottom design, not separate left/right halves.
Rear sight made adjustable for windage and elevation.
Flash hider redesigned to give less muzzle flip and dust signature when fired.
Fully automatic mode replaced with a three round burst, to conserve ammunition in combat.

During the Summer of 1981, the M16A1E1 was tested very thoroughly and was type-classified as the M16A2 in September, 1982, but it was over a year later when it was officially adopted by the Marine Corps on 20 November 1983
---------------
Next:
http://www.globalsecurity.org/milita...t/1986/MVT.htm
(in part)

The penetration results obtained by the NSMATCC with the 5.56mm SS109 cartridge are impressive. The SS109 can penetrate the 3.45mm standard NATO steel plate to 640 meters, while the 7.62mm ball can only penetrate it to 620 meters. The U. S. steel helmet penetration results are even more impressive as the SS109 can penetrate it up to 1,300 meters, while the 7.62mm ball cannot
penetrate it beyond 800 meters. These comparisons however, do not consider the fact that the SS109 uses a semi-armor piercing, steel-cored projectile, while the 7.62mm ball uses a relatively soft anti-personnel, lead-cored projectile. A semi-armor piercing 7.62mm caliber projectile, using second generation
technology as the SS109, would easily out-perform the smaller SS109 projectile in penetration tests at all ranges.22 With respect to barrier and fortification penetration tests, the 7.62mm ball projectile can consistently penetrate two test
building blocks, while the SS109 semi-armor piercing projectile cannot penetrate a single block.
In light of these considerations, the idea of SS109 penetration superiority over the 7.62 x 51mm is not valid.
end
----------
Hmmm, lutefisk you were right about the helmet penetration tests, but as the article above states the "test" actually is not a fair one subsequently the results of the test are somewhat misleading.
Need we find out what a .308 AP round will do and compare with the SS109?
After all the SS109 is more penetrator than ball round.

IMHO the .308 (simply) rules.

BTW - the full article from the last quote makes an extremely good read if one has the time. I enjoyed it alot.

[Sgt_Gold]

Excillent article. I still stand by my statement that the 1-7 twist was to stabilize the tracer round. The following is from www.ammo-oracle.com:

Q. OK, what is all this stuff about rifle twists and different ammo?

Rounds in flight spin for stability because of the rifling on the inside of the barrel. Depending on how much they spin, they are more or less stable in their flight and therefore more or less accurate. The first M16's had a twist rate of 1 complete twist every 14", or 1:14. The next generation had a twist rate of 1 turn in 12". The current A2s and up and the M4 carbines have a much faster twist rate, 1 turn in 7". The reason for the 7" twist is mainly to stabilize the M856 tracer bullet, which is much longer than other rounds. You will recall from above that the M856 was designed to provide 800 meters of trace out of the SAW.

While the slow 1 in 12" twist is adequate to stabilize the 55 grain M193, it will not stabilize the 62 grain M855. As a result, the newer M855 ammo will group 1-2 feet at 100 yards, with bullets flying through the air sideways, instead of shooting to about 2" at 100 yards, like military ammo should.

All this has some ramifications for ammunition selection depending on your rifle's rate of twist.

You can also spin them so hard they fly apart. That's rare, but it happens if you are dealing with very tight twists and very high velocities. When fired at 3200 fps in a 1-in-7 twist rifle, a round is rotating at over 300,000 rpm when it leaves the muzzle. Light, thin-jacketed varmint bullets (i.e., 40gr Hornady TNT or Federal Blitz bullets) often can't take that much spin and will pull themselves apart.

[panzertruppe]

I can't help it any more, I have to say something,
Great topic and seems like everyone is being open minded about replies so here goes...
The first entry was reference a gentleman, Dr Gray, discussing 308 vs 223 and the common points of reference were penetration, expansion, and this application in the military. No real entry of types of weapons and their abilities or disabilities was mentioned.

1) No bullet in the military can expand or its illegal, not even sniper ammo. If it's a purely military application, then that information is not very useful. Maybe in other formats, but not in the military one...

2) Penetration, wow, lots of variables there, I boil it down to CS273 and his reference to physics. Force=Mass x acceleration. The fundamental characteristics of masses, velocities, and what they strike is an incredible endeavor to observe with to many dependant and independant variables. That's where all the experiments can assist and put data into solid empirical data form that is reliable based on its application to the circumstances. Physics will support me here, larger masses maintain more energy over the distance they travel regardless of that distance and the energy imparted, whether penetration occurs or not is still sometimes not critical. That 308 round at 620 meters, a distance very difficult for a standard straight leg infantryman to see much less shoot, is gonna hurt whether it knocks your helmet off or goes thru it.

3) Centrifugal Force=(Mass x Velocity^2) / r , hence the explanation of why lighter bullets break up and fragment. Spin stabilization is not new. That's why we all shoot rifles. Whether the bullets fragments when it hits the target, I'm assuming human and military here, is not crtitcal either because again, although it may tumble, it was not intended to "explode", expand, rend all to hell, its target but to inflict injury so that 3 men are out instead of one.

The debate seems to be centering around Military application, 308 vs 223. So, bottom line, pick the round that posseses all if not most of the following qualities, flat trajectory, greatest stability, good inherent accuracy, imparting the most energy upon impact. Granted, based on Dr Gray's info, I may have grossly simplfied this, but the 308 is all that and some extras versus the 223. It can be conflict dependant, but I'm willing to bet the farm that 308 would not be having any challenge that the 223 is suffering from. I firmly believe that a 6mm round would be the best of both worlds, but after shooting 308 and 223 for many years, I know both are accurate, but one is bigger and goes thru troop transporters, brick walls, helmets, heavy clothing, flak vests, etc, with the above characteristics and that is the venerable 308. The 2 equations above and a wealth of empirical data support this.... Just like the venerable 45, low penetration, low velocity, low pressures, but lots of imparted energy...

Just my 2 centavos..

Panzertruppe

[kotengu]

Also in reference to the helmet tests - look at some pics of the results. It's been awhile since I got these pics (maybe somebody can verify), but IIRC the "testing" was done at 100yds, and the smaller holes were 5.45 and .223.




Not scientific at all - but still pretty impressive!

[panzertruppe]

Kotengu,
I qualify that as SOLID empirical data... Thank you. Pardon error, Dr Roberts, woops.

Panzertruppe