True. It was a multifaceted problem.

by passing by, Monday, May 27, 2019, 11:55 (2008 days ago) @ Charles

Firstly, it seems Remington inflated velocity figures, or cherry-picked lots of early test ammo, and later tests of gun/ammo were not reaching a real circa 3250fps MV. Secondly, the Army had vast reserves of the ball powder which they substituted, and it was dirtier and loaded to higher pressure.

The dirtier problem is a simple fix, which is clean the gun. The original powder gave the impression it would never need cleaning, when the only part of self cleaning to be true is the gas tube, where temps still high enough no condensation/deposits from cooling gas.

Meanwhile, the suddenly converting to M16 Army, who really wanted to stick with their M14 to point of cooking data and skewing tests, fielded the weapons without any provision for cleaning a bare steel barrel and chamber in the tropics. A big part of that was they really thought they had a program ready to sprout forth at any minute a new gun, which would eclipse both the M16 and M14, and they were buying the M16 under duress, and quite convinced it was only a short term fill-in, and paid it almost no mind at all, and set it up for failure.

Back to the switch to the stocks of ball powders, tests were positive in getting the targeted velocity, and they were goal fixated on that velocity. It WAS noted that cyclic rate had increased, and so they changed the weapon specs to match this higher higher observed rate. Only Stoner noted the cyclic rate increase reflected a higher pressure, and how this would change timing out of spec, and eat up 10% engineering safety margin in pressure. And he was ignored.

Turned out it was so fast that bolt bounce and light strikes became common, and a heavier buffer was required. And then bolts started cracking from all the above added stresses. It also turns out early chrome plating of bolt and carrier induced embrittlement to surface of actual steel, fyi.

It was a costly lesson in buying an off the shelf item, and then mucking with it, while having no clue how it works. So, of course, Big Army cintinued to do so, reintroducing many of the exact same problems on a magnified scale, by shortening gas system for even higher pressure, and continuing to boost pressure in every type of ammo adopted since then.

Buffer weights have been progressively increased, buffer springs stiffened in the shorter guns, chroming bolts dropped, specified Carpenter 158 steel heat treated and shot peened for bolts, etc, in compensation, of sorts, to handle these ever higher pressures introduced.

Flipping back again to the powders, the fix(es) were adoption of a cleaner burning succession of ball powders, and ball is standard in all .223/5.56 loads today.

All of which why I say, if you want the gun to run the way it originally designed, and it was outstanding, including early special unit use of same, the special units actually cleaning their guns, and these the non-chromed guns, then going original 20" pressure and dwell time, shooting original spec pressure ammo such as .223 55gr FMJBT, and utilizing improved parts and processes developed for handling modern ill advised pressure hikes, will yield a smooth shooting, reliable, long lasting gun matching the original promise of all those years ago.

Any messing with shorter gas systems and/or higher pressure ammo will introduce compromises to the integrity of the system, and "fixes" never adequate for repairing the degradation of the balance. Same as installing a heavier recoil spring in your fave handgun to shoot those fave hotter loads, you may stop battering on the rearward stroke, but you also just added a huge amount of battering to the area/parts of gun which keep the slide from flying off the end. Better to operate WITHIN design.