ON THE M855A1
Reprinted from Small Arms Solutions and authored by AR-15 expert, Chris Bartocci. -NCS
A Great Round “If” We Had a Rifle Designed to Shoot It!
We have discussed doing a video on the M855A1 cartridge for quite some time. Looking over all the information it seemed to make more sense to do it in a blog article where it could be articulated better. There are several issues with the new M855A1, none of which are based on the performance of the ammunition. Problems are caused by the pressure it is loaded in and the projectile type, which significantly decreases bolt and barrel life of any firearm it is put into.
Shown above is a comparison of the M855, M856 Tracer, early M855A1 and the issue M855A1. The difference between the early and issue M855A1 projectile is the plug under the penetrator. Early projectiles used a tin/bismuth alloy. It was found there was not enough mass to it to properly stabilize in the arctic environment so they switched over to copper. Lead has more mass to it than either the tin/bismuth or copper alloy for the same weight. You have to have more copper to get the same weight. You will notice that the M855A1 projectile is just slightly longer.
Looking at the cross sections you are able to see that both projectiles are made up of three components. The M855 (left) consists of a copper jacket, steel penetrator core and lead plug. The M855A1 (right) is manufactured from a copper jacket, steel arrow head core with a copper plug. The M855A1 projectile fit the Army requirement for a “green” projectile that does not have any lead. This creates a much more expensive projectile. How was the Army able to sell this more expensive projectile? They increased the cost to produce all other military rounds to offset the expense of this new cartridge.
Shown is a US Government comparison chart showing the M855 on the left and the M855A1 on the right. Notice the vital information left out, velocity and chamber pressure. This information is where the metal meets the meat. This is the area that is significantly different between the two that has caused all the controversy. I have seen government spec sheets that include their claim the M855A1 is many steps ahead of the M855. However, I have never been naive enough believe the government gives all the proper info out. Like most things, I never pay attention to what others tell me so I find out for myself. I took M193, M855, M995 and M855A1 to a ballistic laboratory and got all the information. Regardless of what the Army claims, this is an independent test.
Armor Penetration
I procured a 1/2 piece of armor plate. The steel was secured to a railroad tie so it was stationary and would not move. The rifle was a 16 inch M4-type rifle and each shot was taken at 25 yards. One round each of M193, M855, M995 AP and M855A1 were shot.
Looking at the top left is the M193 Ball (FMJ). You can clearly see not much more than a dent. To its right is the M855, only slightly better and you can easily see the slightly deeper penetration due to the steel penetrator. Bottom left is the M855A1. Clearly the M855A1 is superior in hard steel penetration going approximately half way through the armor plate. To that right is the M995 Armor Piercing round which completely penetrated the steel.
Terminal Ballistics
The Army claims that the M855A1 round is superior in terminal performance. They claim that the M855A1 is not yaw dependent. This part of the testing did not necessarily show the new round to be a better terminal performer than the M855.
M855
M855A1
Clearly the tissue damage was better with the M855. The biggest difference was the Initial Yaw began at 1.25 inches on the M855 and the M855A1 started earlier at 1 inch. The M855A1 completely fragmented, retained nothing. The M855 retained 48.2% of its weight. Now this type of gel is not an exact match for human tissue. It does not take into account the different density of various types of tissue/organs. It also does not take into account bones. I would be far more likely to say wounding tissue damage was closer to comparable.
Mechanical Issues With M4/M16-Series, as Well as Others
The biggest problem with the M855A1 ammunition is the way it is loaded. It is NOT loaded to the 5.56mm NATO specifications, which all 5.56x45mm caliber rifles are designed for. This is clearly in violation of the NATO standardization contracts. 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. The M855A1 was designed to give 20″ barrel performance in a 14.4″ barrel. 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.
As you saw in the government released info on the M855A1, they did not release muzzle velocity or chamber pressure. There had been many rumors going around as to what the specifications actually are. 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.
M855
M855A1
Looking at chamber pressure, both cartridges were fired in a 14.5 inch M4A1, both projectiles are a 62 grain projectile. 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. The M855A1 is increased vastly to 61,830. In fact, you see pressure levels as high as 62,900 psi. Please keep in mind that a proof cartridge is 70,000 psi. Clearly the rifle is being significantly driven past its design parameters. The increase in chamber pressure also increases the bolt velocity substantially driving the cyclic rate much faster, which increases parts wear and service life of both the bolt and barrel.
Bolts have been known to break within 3,000 rounds and barrel life has been cut by 50%. This is NOT a deficiency in the M4 carbine. The first time the M855A1 ammunition was tested was not in M4/M16 rifles. It was conducted during the Individual Carbine completion, which not one of the entries stood up to the M855A1, and none completed the endurance testing. All of the entries were designed around the M855 ammunition and worked excellent and passed all the military testing internally at the manufacturers prior to military testing. The bottom line is that as good as this round may perform, neither the U.S. nor any of our allies have any rifles that will stand up to the high pressures of this round.
Feeding Problems
Due to the shape of the projectile, as well as the hardness, feeding the M855A1 through a standard GI magazine caused problems. The projectile was not introduced high enough to fully clear the feed ramps on the barrel extension causing the hard sharp tip of the projectile to damage both the upper receiver, as well as the feed ramps, and end of the barrel extension. This damage was