Clearly the rifle is being significantly driven past its design parameters. Please keep in mind that a proof cartridge is 70,000 psi. In fact, you see pressure levels as high as 62,900 psi. The M855A1 is increased vastly to 61,830. The M855 has an average chamber pressure of 51,522 psi, which is within the 52-55,000 psi range the M4 and all 5.56mm military rifles are designed. Looking at chamber pressure, both cartridges were fired in a 14.5 inch M4A1, both projectiles are a 62 grain projectile. So to come up with undisputable facts of what all these numbers are, I tested in a ballistics laboratory both the M855 as well as the M855A1 for comparison purposes. There had been many rumors going around as to what the specifications actually are. Part of this was a change in the propellant change which brought pressures higher to peak at the shorter carbine gas system rather than rifle length gas system.Īs you saw in the government released info on the M855A1, they did not release muzzle velocity or chamber pressure. The M855A1 was designed to give 20" barrel performance in a 14.4" barrel. The Army has not been forthright to anyone, including our allies, to the extremely higher port and chamber pressures that will cause bolt breakage, damage to receiver extensions, upper receivers and cause a barrel to wear 50% faster. This is clearly in violation of the NATO standardization contracts. It is NOT loaded to the 5.56mm NATO specifications, which all 5.56x45mm caliber rifles are designed for.
The biggest problem with the M855A1 ammunition is the way it is loaded.
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