Ballistic Protection standards reference

[The Dark]

Originally Posted by "swaghauler'

Additionally, look at the new M855A1 ammo (with a 13% increase in velocity to more than 3100fps in a 62-grain projectile), It cuts right through an NIJ Level 3 vest at short range and STILL behaves like a Soft Point bullet inside the target. It could be as much of a "game changer" as MK282 was when it was introduced.

There are still issues with the M855A1, although not related to penetration. When American Rifleman tested the round, about 20% were flyers (and that was a test this year, after the bismuth alloy that deteriorated in hot weather was supposedly fixed). The accuracy also isn't quite as good as advertised, because the tests were done with a tighter twist than service rifles have (either 1:8 or 1:9, instead of 1:7). The current standard for approval is 5.5 MOA.

Also, the ballistic trajectory isn't the same, so all the rifle sights (from iron to red dot) will need to be changed. It's fairly close up to 200 yards, but beyond that it rapidly diverges to a six inch change in elevation.

It also causes port erosion in M4 tests due to the much higher pressure, which affects automatic fire rate and increases jamming. A SOCOM test found that on average, a rifle firing M55A1 would crack a locking lug every 6,000 rounds. Even without a catastrophic failure of the rifle, barrel life is reduced by around 50% due to the high pressure of the round.

All of these problems can be overcome, through improved quality control and toughened internals. As for penetration, the information I've seen is that it will penetrate NIJ III armor, but will not penetrate SAPI. When the Wound Channel tested the round, it went through III easily. Against III+, it failed out of a 16" barrel but penetrated out of a 22" barrel (it also didn't generate nearly the advertised velocity, being 2960 fps out of the 16" (and 3259 out of the 22")). Unless TWC had some underpowered rounds, the M4 won't generate the advertised velocity (though the M16 should). This probably explains why the USMC (which intends to use the M4 only) is using the Mk318 SOST ammunition at 2925 fps from a 14" barrel instead of the M855A1.