Exploding M-16's ????

[irishsteve]

I was looking at one of Patrick Sweeneys AR15 books,and it said that all chrome bores are 5.56 chambered so If you have a C stamped on your barrel you should be good to go with mil spec ammo.

[gew98]

Most of all of this sounds like bunk to me. I fired up oodles of M16's while in uniform , mini14's ( yuk ) and wads of other223/5.56 rifles. The only ammo problem I encountered was the A2 rifling twist (1-7) did not stabilize the M193 bullet and the A1's (1-12) did not like the M855 bullet. And for that matter I don't care for the "product improved" M855 bullet either. I see a 1-9 twist AR and I still think of it as "compromise twist".
The only AR blowup I have seen was an H&K video on how they could submerge their 416 piston upper in water pull it out and immeadiately shoot it. While they did the same thing with a standard A2 and it literally blew the upper into scrap - big pieces lost there !.

[Col. Colt]

gew98,
It's not bunk because some AR makers (not Colt) have offered "Match" barrels with the tighter, .223 Commercial "Bolt Action" spec chamber - having a much shorter throat than military spec. If you take a 5.56MM round, loaded to max pressure and with the bullet set out to the proper length for a military throat and chamber it in a .223 Commercial chambered rifle, the bullet may be forced into the rifling upon chambering, creating much higher than normal pressures. With the .223/5.56 cartridge, the result is sometimes a blown or pierced primer and gas released into the shooters face - not good for either the gun or the shooter! The specs are not quite the same, period. The good news is that the military 5.56MM chamber is in the vast majority of ARs - and it works with both ammo types just fine. But there is always the exception...... CC.

[limazulu]

gew98,
It's not bunk because some AR makers (not Colt) have offered "Match" barrels with the tighter, .223 Commercial "Bolt Action" spec chamber - having a much shorter throat than military spec. If you take a 5.56MM round, loaded to max pressure and with the bullet set out to the proper length for a military throat and chamber it in a .223 Commercial chambered rifle, the bullet may be forced into the rifling upon chambering, creating much higher than normal pressures. With the .223/5.56 cartridge, the result is sometimes a blown or pierced primer and gas released into the shooters face - not good for either the gun or the shooter! The specs are not quite the same, period. The good news is that the military 5.56MM chamber is in the vast majority of ARs - and it works with both ammo types just fine. But there is always the exception...... CC.

The more I read these posts the more I question them. The magazines are the same for the .223 commercial and the 5.56 cartridge so if it fits the magazine then how can it get jammed into the rifling? The tighter cut chambers still won't cause a round to go into the rifling if the cartridge is magazine length.

I thought the problem had more to do with headspace issues and the potential for slam fires.

[Col. Colt]

Throat length, guys. Period. And the mag has lots of room and has nothing to do with it - we are talking in a few thousanths of an inch making a major difference in pressure. Hugo has another post regarding Olympic arms ARs on this board with a diagram that shows the difference in the throats. It isn't the "chamber", it's the distance between the bullet and the rifling created by the relationship of the loaded round and the throat, the angle of approach, etc. And it Matters! As an LE AR Armorer and a former Service Rifle shooter, trust me on this. Or read about it in Zedeker's "The Competitive AR-15".

[AKA Hugh Uno]

actually tends to mean a more GENEROUS length (to ensure the feeding of 69+ grain bullets). Usually this is a Wylde chamber or variant. Again, I doubt that ANY major manufacturer of AR rifles has ever shipped one out that has a true 1960's era bolt gun SAAMI chamber. In fact, the bolt guns made post 1970's also tend to have longer chambers also. All have decent amounts of freebore and very shallow leade angles (i.e. 1 degree vs. 3 degrees).

Frankly, I don't even think it is POSSIBLE to "blow up" (or even get pressure problems/warnings) with ANY commercially made AR rifle from a "name" manufacturer. This INCLUDES so-called "match" chambers as this virtually always means a LONGER throat and shallower leade angle.

Bushmasters "match" chamber is 1 degree, 30 minutes and allows OAL of from 2.450+ compared to SAAMI OAL of 2.250-2.30. Bottom line, if the GI or commerciaL round GOES IN, SHOOT IT.

[lyman1903]

Brad, there are no dumb questions - it's only dumb when you fail to ask and get yourself in trouble due to pride!

Many Match handloaders tailor there accuracy loads to the individual chamber by seating the bullet to the "most accurate" length. You would want to be pretty advanced in your handloading knowledge and practice before you attempt this, and special tooling is recommended.

I suggest you read up on the subject extensively and talk to some advanced loaders, but until you feel competent, stick with the specs in the Handloading Manuals. (Also, an AR has a maximum length due to the magazine itself to consider.) Get ahold of Zeddiker's (sp?) book "The Competitive AR15" and give it a read - it will explain. Cheers, CC.

+1 on Zediker's books, both the AR15 (the mouse that roared) and his match handloading book are , IMHO, must reads,

try zediker.com for info, and he has some good articles there too,

[Jim K]

So a bullet pushed into or against the rifling before firing will cause a gun to blow up? So thousands of competive shooters with other rifles have their barrels chambered and/or the bullets set out to do just that. (A long leade will allow the bullet to skid when it takes the rifling, affecting accuracy.)

But the AR-15 is different? What works for other rifles causes an AR-15 to blow up in a mushroom cloud?

At the pressures involved, a normal bullet acts like silly putty; it will move into the rifling with no problem. The only thing that can raise pressures would be too tight a chamber neck that would not allow the bullet to release properly. And that should not differ between commercial and military ammo.

I think some "experts" are off the track.

Jim

[gew98]

I have to agree Jim. A buddy I knew in the peoples republik of new jerky used to do benchrest . He called it "soft loading". That is he would seat his bullets out further and not crimp. When the round was chambered the bullet would meet the rifling and get slightly set in it and the rest would be pushed back in the case as the bolt closed home. It does cause a bit of a pressure bump , but nothing alarming. I have seen overlength rifle brass with crimped bullets that were more dangerous than softloading by far when chambered tight for obvious reasons. If someone is too lazy or casual to be bothered by trimming their brass to length they deserve what they get.

[AKA Hugh Uno]

between the barrel, barrel nut, and extension, plus the locking lugs on the bolt, it can handle any normal pressure with ease.