The Army's Picatinny Arsenal, which conducted the study, has this to say:

The study sought to answer whether any commercial, off-the-shelf 5.56mm bullets that perform better than M855 against unarmored targets in Close Quarters Battle might be available.

It was limited further to determining if the Army could quickly purchase and field a possible replacement for the M855 and did not consider replacing the current inventory of 5.56mm weapons with weapons of another caliber.

“This was not a caliber study” Rider said. “However, it did find that the current family of 5.56mm weapons and the older 7.62mm M14 have the same potential effectiveness in the hands of a Warfighter during the heat of battle.”

The study also showed an increase in lethal potential when the marksmanship technique of firing controlled pairs, i.e. firing two rounds in rapid succession, was used.

The present edition of the M16 is the M16A2, introduced in 1985, as I recall. The 'A2 has a full-auto setting that fires only three rounds, no more, per trigger pull. It also shoots semi-auto, of course. The reason for this setting is that on unrestricted full auto firing the fourth and subsequent rounds wind up going skyward, a symptom of full-auto handheld guns since the Thompson submachine gun. IIRC, one soldier per fire team is normally designated as a automatic rifleman and in combat he would normally be the only one who routinely shoots his M16 on full auto, repetitively sending bursts of three downrange.

Not any more. If every soldier now understand that he has to shoot a bad guy twice to ensure a kill, then he'll reasonbly figure, "If two is good, three is better," set his rifle on auto, and rock and roll every time. Besides, the automatic cyclic rate of fire of the rifle is 800 rounds per minute, or 13 rounds per second. That's much faster than anyone can achieve pulling the trigger twice. (My guess is that a lot of troops have been three-bursting all along.)

I must say that the study's finding that "the older 7.62mm M14 have the same potential effectiveness" is rather difficult to believe. The 7.62mm basically is a .30-caliber bullet, which was the Army's standard diameter round since 1906 (hence the "30-06" round). This cartridge was used throughout World War II in the Garand rifle, "The greatest battle implement ever devised," according to this authority.

Top - .30-06 round; bottom, 5.56mm round

I'm not suggesting that the Army re-adopt the .30-06 round. There are alternatives to both it and the M855, 5.56mm round that offer many of the advantages of both. The '06 had stellar knock-down power and was heavy enough to rip through truck engines, surely an excellent capability for a time when car- or truck-mounted IED's are common. The 5.56mm round is lightweight, which means a grunt can carry a lot more of them than the '06. It also means that the rifle can be lighter: the M 16A2 weighs more than a pound less than the M1 Garand. There was consideration to developing a 6.8mm round for the XM8 rifle, but the XM8 project settled on the present 5.56mm (M855) round before being canceled last fall.

There was some discussion for awhile, I recall, to re-introduce the 7.62mm NATO-standard round in a new infantry rifle, but it never went anywhere. This round is highly effective in combat with excellent range, very good material penetration and knockdown power. The round was used in the M14 rifle and the famous M60 series medium machinegun, both introduced in 1957. The M14 was based on the M1 Garand and featured a 20-round magazine rather than an eight-round clip.

The M855 round was introduced for the M16A2. It replaced the 'A1 and earlier models, which all used the M193 round. The M855 bullet is longer and heavier and slower out the muzzle than the M193. The replacement was made for two main reasons: increase the maximum effective range and achieve commonality with the M249, 5.56mm Squad Automatic Weapon (SAW), a light machinegun for infantry squads that replaced the M60, 7.72mm machinegun. Achieving an effective range of 1,000 meters for the SAW while retaining the 5.56mm round required the heavier M855 round. The M16A2 was introduced to enable all the weapons of an infantry squad to use the same ammunition.

Paradoxically, the heavier round sacrificed lethality at the short ranges of typical infantry-rifle combat. As I noted three years ago, rifle-combat ranges have not changed since 1917, about 20-30 meters. A technical explanation of wound ballistics can be found here, but the short version is this. Immediately incapacitating wounds from full metal jacket bullets, the only kind allowed by warfare conventions, come from the bullet tumbling and fragmenting in the body. All FMJ bullets will tumble (except in flight, of course) because their center of gravity is well behind the nose, but just when depends on their speed. The 5.56mm round tumbles and fragments when it slows to 2,700 feet per second. With greater inertia than the older M193 round, the heavier M855 slows after impact less readily. Thus, unless it hits bone, it will fly straight in and out without causing an immediately incapacitating wound, as the Army's study report notes.

There is no quick fix to this conundrum. The M16A2's chamber is designed for the longer M855 bullet, as is the SAW's. So the older M193 round can't just be reissued. And no replacement weapon or round is in the works. So the Army tells the troops, "shoot 'em in the head, twice."

Dunnigan concludes, in masterful understatement, "The army report is not likely to be well received by the troops."

BTW, the 9mm pistol is almost worthless, too.


Cross posted at donaldsensing.com.