Q. What types of ammo has the US Military used in its M16s and M4s?
The military has used the following ammo types in 5.56mm (excluding blanks and specialty rounds):
M193: 55gr FMJBT Ball, plain tip.
This cartridge is intended for use against personnel and unarmored targets from 5.56×45mm weapons with a 1-in-12-inch (1:12) or faster rifling twist rate (M16 family rifles and other compatible systems). Its ballistic coefficient is typically .243
M196: 55gr Tracer, short range, red-painted tip.
M855: 62gr FMJBT Ball, green-painted tip.
This cartridge is intended for use against personnel, unarmored and light armored targets from 5.56×45mm weapons with a 1-in-10-inch (1:10) or faster rifling twist (Machine guns: M249 Minimi; Rifles: M16A2 and other compatible systems). The M855 cartridge is based on the FN-designed SS-109 bullet, and has a gilding metal-jacketed, lead alloy core bullet with a steel penetrator. The primer and case are waterproof. It was adopted by NATO in 1980 as the standard small arms ammunition for NATO forces. Its ballistic coefficient is typically 304.
M856: 61gr Tracer, long range, orange-painted tip.
This cartridge uses the FN-designed L-110, 63.7 grain tracer bullet, which has no steel penetrator. (Note that while FM 23-14 lists this bullet weight for the M856, IMI lists the weight of the L-110 tracer bullet which tops the M856 round as 61.7 grains. At least one AR15.com member reports 60.8-61.3 weights for a variety of M856 rounds that were pulled). The long projectile requires a barrel with a 1:8 or faster rifling twist.
M995: 62gr FMJBT AP, black-painted tip. This FN-designed bullet uses a hardened tungsten-carbide penetrator, and is only available on special-issue SAW belts.
M996: Actually, XM996, as it hasn't been adopted yet. The tracer compliment to M995.
Left to Right: M193, M855, M856, Sierra MatchKing HPBT.
Component view of M995 Armor Piercing 5.56mm.
Fact: The specifications for the various rounds are:
M193: Defined by: Mil-C-9963F 55 grain bullet (q 2 grains) at a muzzle velocity of 3,165 (q 40 fps) from a 20" barrel @ 78 feet from the muzzle. Accuracy: maximum of a two inch mean radius at 200 yards from ten 10 shot groups (~3 MOA). "Statistically average" M193 ranges from 1.2 to 1.6 inches mean radius, which is equivalent to 1.8 to 2.4 MOA. Velocity runs about 3,200 fps due to gas loss through the port. Accuracy is typically around 2 to 2+ MOA from an M16A1 rifle at ranges of 100 to 300 yards. M193 ammunition should have 1:12 twist or faster. M193 is barely stabilized with 1:14 at ambient temperatures and will not stabilize at all when the air temperature drops below freezing.
M855: Defined in MIL-C-63989 NATO specifications for M855 Ball require a 61.7 grain (q 1.5 grains) with a hardened steel penetrator at a velocity of 3,000 fps (q 40 fps) from a 20" barrel @ 78 feet from the muzzle. Typical velocity 15 feet from the M16A2's muzzle is 3,100 fps. Accuracy: maximum of approximately four MOA over the 100 to 600 yard range. Typical accuracy of average lots in an M16A2 is about 2+ MOA. This round must also penetrate a nominal 10 gauge SAE 1010 or 1020 steel test plate at a range of at least 570 meters (623 yards). The M193 round will penetrate this same plate reliably at 400 yards and about half the time at 500 yards. The 5.56mm and 7.62mm NATO rounds will penetrate it reliably out to 700 yards or more. Because the steel penetrator increases the length and changes the weight distribution of the SS-109 bullet, it is suitable for use only in barrels with a twist of one turn in nine inches or faster. 1:10 twist will barely stabilize this round and not below zero degrees F.
Reloaders: Both M855 and M193 in the US generally use Olin Ball WC844 propellant. Apparently H335 is roughly equivalent to WC844.
Cross sections of various rounds.