Marginal aspects of AR design.

[Robenstein]

The lethality of the 5.56 NATO round has been decreased by the evolution of the design. The initial tests in Vietnam in the early 60's by the military advisers reported it was a surprisingly lethal round. And this came as a comparison to what they were used to, the Soviet M43 intermediate round, the old 30M2(30-06), and the 7.62 NATO round.

The first decrease came when they tightened the twist from 1 in 14 to 1 in 12 to again meet the long range accuracy requirements of the military in the Arctic trials at Fort Greeley. One report near the end of Vietnam reported this alone may have reduced lethality by up to 40 percent. The original twist rate resulted in a nearly unstable round that killed so many that advisers actually complained they had so few wounded prisoners to interrogate.

Then came the change again to tighten the twist with the product improvement project that resulted in the M15A2.

Then came the shortening of the barrel to the current M4. To somewhat compensate they have made heavier bullets, but the original premise of the small caliber high velocity intermediate round was to create a small and light round that at a high velocity would dump its kinetic energy into the target making it as lethal or more so than the larger caliber rounds it replaced. All the while allowing a U.S. soldier to carry nearly 2x as many rounds. With heavier rounds, that are more stable, and slower, the lethality is not nearly what it most likely was.

 

[hatt]

Originally Posted By: Robenstein
The lethality of the 5.56 NATO round has been decreased by the evolution of the design. The initial tests in Vietnam in the early 60's by the military advisers reported it was a surprisingly lethal round. And this came as a comparison to what they were used to, the Soviet M43 intermediate round, the old 30M2(30-06), and the 7.62 NATO round.

The first decrease came when they tightened the twist from 1 in 14 to 1 in 12 to again meet the long range accuracy requirements of the military in the Arctic trials at Fort Greeley. One report near the end of Vietnam reported this alone may have reduced lethality by up to 40 percent. The original twist rate resulted in a nearly unstable round that killed so many that advisers actually complained they had so few wounded prisoners to interrogate.

Then came the change again to tighten the twist with the product improvement project that resulted in the M15A2.

Then came the shortening of the barrel to the current M4. To somewhat compensate they have made heavier bullets, but the original premise of the small caliber high velocity intermediate round was to create a small and light round that at a high velocity would dump its kinetic energy into the target making it as lethal or more so than the larger caliber rounds it replaced. All the while allowing a U.S. soldier to carry nearly 2x as many rounds. With heavier rounds, that are more stable, and slower, the lethality is not nearly what it most likely was.


There is no difference in M193/M855 terminal performance whether you use 1/14, 1/12, 1/9, 1/8, 1/7 twist. Tissue is so much more dense than air any twist will result in rapid bullet yaw.

Decreasing barrel length has had an impact on performance. Less speed less fragmentation, less damage. But clearing houses and getting in and out of vehicles dictates the more compact guns. The clear option is to stop the nonsense of fielding inferior bullet designs and start using the most effective designs.

 

[Robenstein]

On page 221 of Ed Ezell's book "The Black Rifle" is a report from the Ballistics Research Laboratory itself in 1966 ...and I quote" The 1:12 twist yields equivalent or higher hit probabilities than the 1:14 for all ranges, temperatures, and aiming errors. But less kills per hit and maybe less kills per shot. The 1:12 doesn't tumble as easily as the 1:14" I am guessing the BRL would know more about the effects of gyroscopic stability/instability on the performance of the round than I do, so I defer to the experts.

 

[bsmithwins]

Originally Posted By: Robenstein
The lethality of the 5.56 NATO round has been decreased by the evolution of the design. The initial tests in Vietnam in the early 60's by the military advisers reported it was a surprisingly lethal round. And this came as a comparison to what they were used to, the Soviet M43 intermediate round, the old 30M2(30-06), and the 7.62 NATO round.

The first decrease came when they tightened the twist from 1 in 14 to 1 in 12 to again meet the long range accuracy requirements of the military in the Arctic trials at Fort Greeley. One report near the end of Vietnam reported this alone may have reduced lethality by up to 40 percent. The original twist rate resulted in a nearly unstable round that killed so many that advisers actually complained they had so few wounded prisoners to interrogate.

Then came the change again to tighten the twist with the product improvement project that resulted in the M15A2.

Then came the shortening of the barrel to the current M4. To somewhat compensate they have made heavier bullets, but the original premise of the small caliber high velocity intermediate round was to create a small and light round that at a high velocity would dump its kinetic energy into the target making it as lethal or more so than the larger caliber rounds it replaced. All the while allowing a U.S. soldier to carry nearly 2x as many rounds. With heavier rounds, that are more stable, and slower, the lethality is not nearly what it most likely was.



The kicker is that at least you have a chance at close range of getting tumbling at fragmentation with 556 NATO. With the heavier, slower 762 NATO, .30-06, and 8mm Mauser you're more likely to get icepick type wound profiles where the bullet drives straight though doing minimal damage unless bone is hit.

BSW

 

[Robenstein]

Yes and no, since there are things you can do to the larger full power rounds to make them tumble and be more lethal. I do believe the old West German 7.62 NATO had a tendency to destabilize more than its counterpart NATO rounds and was noted as being pretty lethal, and the Brits did put wooden tips in their old 303 rounds that caused them to deform and yaw. The Soviets also modified their 7.60x54R to do that also, but again in sniper round form like the Brit 303.

But you are right, the old school rounds with traditional construction hit and departed little of their kinetic energy relying on the permanent wound cavity as well the the hydrostatic shock wave to kill. I cant remember or find the article, but with the current heavy rounds and short M4 barrel, the velocity needed to fragment in the current M4's is around 100 yards. While this works in urban combat, it is totally insufficient in more open combat. I am thinking that at 200 yards you would be getting 22 caliber sized ice pick type wounds versus 30 caliber. At that point, the bigger slug is going to win in the theater of lethality.

 

[hatt]

Originally Posted By: Robenstein
On page 221 of Ed Ezell's book "The Black Rifle" is a report from the Ballistics Research Laboratory itself in 1966 ...and I quote" The 1:12 twist yields equivalent or higher hit probabilities than the 1:14 for all ranges, temperatures, and aiming errors. But less kills per hit and maybe less kills per shot. The 1:12 doesn't tumble as easily as the 1:14" I am guessing the BRL would know more about the effects of gyroscopic stability/instability on the performance of the round than I do, so I defer to the experts.

Quote:
The U.S. Army Wound Ballistic Research Laboratory conducted terminal performance testing using 5.56 mm 55 gr M193 FMJ ammunition fired in 20” barrels of 1/14, 1/12, 1/9, and 1/7 twist rates. No difference in terminal performance was noted between shots made with the different twists.

DocGKR

Ammo Oracle

 

[Robenstein]

Yes because the internet trumps books in the reliability of information, especially a book written by man who was the curator at the Smithsonian's national firearms collection(Not a job a historian gets by publishing bad or wrong information) and who had the BRL report of 1966 in his hands and cites it in his book.

I never said the 1 in 12 twist did not cause tumbling, but that the 1 in 14 caused it to tumble better. This is what the BRL report of 1966 says. Also the ARPA field tests under project AGILE showed devastating wounds and lethality that was not evident upon the adoption of the 1 in 12 system that was adopted not only for accuracy reasons, but also because Colt reported having difficulty with the manufacture of 1 in 14 barrels.

 

[hatt]

Doc is pretty well respected in the ballistics realm. And likely much more informed than a museum curator who read a report one time. The same with the Colt having trouble manufacturing 1/14 barrels. What possible trouble could they have had. It's likely the M16 started off with that twist because 1/14 was the most common twist used for .224 calibers back then. But all the sudden a major barrel maker forgot how to make them?

 

[Robenstein]

Read Ezell's book. It is not that Ezell and his co author Stevens read the report and wrote about it, in the book there is an excerpt from its conclusion right there on the page, which I quoted in my post. Those were the words of the BRL report to General Besson exactly as it was written word for word from the project management officer who oversaw the study.

Colt had trouble making rifle barrels in general at that time. You must remember that Colt had not made a rifle in many many years when they bought the AR design from Armalite. Just like when they went to chrome line the barrels later, there were teething problems since they had issues chrome lining such a small bore.

 

[hatt]

Yeah I'm not going to be buying a $50 book to argue about stuff that doesn't even matter today. M193 bullet performance out of 1/12 vs 1/14 barrels and possible Colt barrel teething issues and all the other historic stuff that gets brought up constantly have 0% relevance today when discussing the current AR15 platform.

 

[bsmithwins]

Originally Posted By: hatt
Yeah I'm not going to be buying a $50 book to argue about stuff that doesn't even matter today. M193 bullet performance out of 1/12 vs 1/14 barrels and possible Colt barrel teething issues and all the other historic stuff that gets brought up constantly have 0% relevance today when discussing the current AR15 platform.


They have these things around where I live called a 'library'.

They often keep books at a library. Frequently, the nice people that organize the books will borrow it for you from another library if they don't have it themselves.

BSW

 

[hatt]

LOL, I won't be going to the library either because something was wrong on the internets. You are free to research all you want about obsolete twist rates that aren't even produced anymore along with 60 year old military bullet technology and how those things effect current guns. Maybe tell us how Mattel was building M16s. I just don't really care.

Do you have anything to add that's relevant today?

 

[Robenstein]

Originally Posted By: bsmithwins
Originally Posted By: hatt
Yeah I'm not going to be buying a $50 book to argue about stuff that doesn't even matter today. M193 bullet performance out of 1/12 vs 1/14 barrels and possible Colt barrel teething issues and all the other historic stuff that gets brought up constantly have 0% relevance today when discussing the current AR15 platform.


They have these things around where I live called a 'library'.

They often keep books at a library. Frequently, the nice people that organize the books will borrow it for you from another library if they don't have it themselves.


BSW


+1 They even have this thing called interlibrary loan where if they don't have it they can borrow the book from another place to borrow it to you. I know I used the heck out of this when I was writing my masters thesis and dissertation.

 

[punisher]

....and on a more lighthearted note......

Early 1990s, after Eastern Europe finally got free of the Soviets, and the Soviet Union collapsed, there was a big scramble for money in the former satellites. Some sharp entrepreneur(s) saw leftover Soviet military ammo factories, and a lot of surplus components just sitting there for the taking. Some quick retooling and soon there were millions of rounds of incredibly low grade steel case 5.56 and a lesser amount of 7.62 ammo being exported westward.

Got suckered into an "incredible deal", fortunately it didn't cost me much money, and but a few hours of cleanup time on my ARs. 10 round strippers, stacked I don't know how many thousand to a case. Each strip was $1 each, 5 strips for $8. $80 was chicken feed, so what the heck. I got 50 clips and figured if nothing else, good SHTF ammo.

First problem at the range, 5" groups at 50 meters from an A2 H-bar that normally printed 1" with good ammo. 100 meters, maybe a CEP of a foot. I sent 20 rounds downrange, maybe 10 hit the target. After most of one 30 round mag- rifle just refused to fire and the bolt pretty much decided to stay in battery. I had looked at the fired cases previously, no strange pressure signs, primers looked OK, cases bulged in front of the head, but I figured small base ammo, plus it was the first (and last time) I fired steel cases.

At the house I had to beat the stuck round out with a cleaning rod. Whatever the lacquer/varnish finish was on the cases decided to melt and stick a case in the chamber like Gorilla glue. Took hours with acetone to get everything cleaned up. Gas piston, and bore were coated on some sort of nasty crud. Sacrificed a few rounds, pulled the bullets, sawed bullets and cases, and found out what happens when "quality control" is just some letters to a former communist. Bullet cores were visibly off center. Jackets=non concentric. Jacket material- some sort of metal (zinc?), unknown with copper plating. Cartridges- not too bad. Berdan primed, no serious manufacturing defects, but I cannot vouch for the materials. Gave away 450 rounds.....with warnings.

AR isn't perfect, but compared to the competition, and the price, I will take it. You have trade offs, granted. I got my first AR 28 years ago. Built countless others. I will take the devil I know vs the one that I don't.

EDIT: and the powder smelled like pee

 

[j_mac]

Why are we still equipping our entire military with the "M-16" design that has been proven to be unreliable so many times. I mean there are a myriad of weaknesses this design exhibits when subjected to battlefield stress. But WE ARE STILL BEATING OUR HEAD AGAINST THE WALL. Isn't it time to adopt the HK G36 or something? ANYTHING!?

 

[Robenstein]

The U.S. Military has been very frugal historically with rifles, especially after the dawn of the "Atomic Age" when funding went to missiles, bombers, jets, ect. And the AR platform is so economical that it would take a rifle that is in a whole other league not only in reliability but accuracy, durability, ergonomics, and lethality to hurry its departure. It would literally have to make the AR platform look like it was a Krag rifle.

 

[hatt]

Originally Posted By: j_mac
Why are we still equipping our entire military with the "M-16" design that has been proven to be unreliable so many times. I mean there are a myriad of weaknesses this design exhibits when subjected to battlefield stress. But WE ARE STILL BEATING OUR HEAD AGAINST THE WALL. Isn't it time to adopt the HK G36 or something? ANYTHING!?

That's funny. The German army is talking about "significant shortcomings" and 24 inch groups at 100m after firing 90 rounds with the G36. And also please give some of the details of how your M16 failed you while you were in the military? The military just completed a study and none of the other designs offered significant advantages.

 

[95busa]

I have seen m16/m4 jams but cannot recall the last time I saw breakage. Most jams I saw were basic training A2s that had all the park burnt off them from being shot so much. Everything has a weak point. The AR works pretty darn good, and contrary to popular opinion I have never seen anyone shot with them get up and walk it off.

 

[95busa]

Oh yeah, and put an ACOG on it and its like clubbing baby seals. The things shoot GOOD.

 

[j_mac]

My personal experiences with Colt and Bushmaster ARs indicate that they will Jam occasionally. The Colts I've seen seem to jam more than the Bushmasters. Its no wonder that Colt has lost the production rights for our military ARs to Fabrique Nationale. If I were fighting in an urban street battle and came across a real Russian or former Warsaw pact AK, I would throw down my AR and pick up the AK. The worst possible scenario in combat is for your weapon to stop working. The enemy does not wait for you to clear a jam or clean your rifle.
A good AK will simply NOT stop shooting.