American Rifle - Alexander Rose [200]
An historian who interviewed an officer who had been present during the field trials recalled that it was “impossible to take prisoners using the AR-15 because even minor wounds proved fatal.”
The ARPA report’s findings prompted its readers in Washington either to become convinced advocates of the AR-15 or to guffaw. Claims as to its lethality, the latter argued, were outlandishly absurd and clearly exaggerated. Their point was lent some credence by the inability of any-body to replicate the astounding results obtained in Vietnam. The Army Wound Ballistics Laboratory at Edgewood Arsenal used ballistic-gelatin blocks and anesthetized goats as stand-ins for Vietcong guerrillas but failed to reproduce the expected wounding characteristics. Had the ARPA reports been faked?
The anomaly was easily explained. The degree of “twist” in a barrel’s grooved rifling governs how rapidly the bullet revolves as it races out of the muzzle, like a football spiraled by a quarterback. Twist is measured in terms of inches, so that a one in twelve-inch twist means that the bullet rotates around its axis once every foot; a one in ten-inch twist is thought to be “tighter” than a one in twelve, a one in fourteen, “looser.” At its simplest, the tighter the barrel’s twist, the faster a projectile spins and the stabler its flight. A stabilized bullet is more accurate than an unstable one, though when determining an appropriate twist for a particular bullet, its weight, velocity, and shape, as well as the range to target, weather, and barrel length, must be taken into account.
The Springfield Model 1903 and the M1 were both given, after much trial-and-error testing by Ordnance armorers, a twist of one in ten inches and the M14, one in twelve. In order to compensate for his .223 bullet’s relative lack of striking energy by slightly destabilizing it, Stoner had suggested a looser twist of one in fourteen inches. Since he was expecting the AR-15 to be used almost exclusively at short ranges (25 to 150 yards), by wobbling its bullet a bit the energy differential wouldn’t matter so much. This was because a relatively unstable bullet is more likely to fragment and tumble once it leaves the air and enters the denser medium of tissue. The .223 still would not hit as hard as the 7.62mm, but once inside it would cause greater damage.
The unreproducible, remarkable ARPA results were caused by Colt’s antiquated machinery being unable to carve Stoner’s specified rifling twist of one in fourteen inside the barrel. Instead, in these early models the barrelmen had plumped for one turn in sixteen or even eighteen inches. Stoner’s original specification had ensured essentially stable flight with a touch of jiggle, but Colt’s modification made the bullet travel at the ballistic equivalent of a bumblebee’s erratic flight. The cumulative effect of the projectile’s singular combination of instability, fragmentation, velocity, and hydrostatic shock when it collided with flesh, blood, and tissue was what produced the gushing, gaping wounds described in the ARPA report.46
The furor over the AR-15’s performance—was it spectacular or not?—attracted Secretary of Defense McNamara’s notice. In fact, McNamara had discreetly had his eye on the problem as early as December 27, 1961: it was he who had signed the order approving the ARPA shipment of one thousand AR-15s to Vietnam, bypassing Ordnance.47 Owing to its M14 production delays, that corps had long since lost his confidence, and on May 8, 1962, McNamara merged it with six other technical bureaus—most of which dated back to the Revolutionary War and the early days of the Republic—into a single, sprawling entity called Army Matériel Command (AMC). At a stroke, the post of Chief of Ordnance had been abolished. (It would be resurrected in 1985.) The first head of AMC was General Frank Besson, originally commissioned in the Corps of Engineers (which was also vacuumed into the new