utilización y mantenimiento
NORMAS PARA LA UTILIZACIÓN DEL EXTINTOR DE INCENDIOS
In light of the fact that the AR-15 rifle characteristically may allow the primer to be struck by a firing-pin blow of about 10 or 15 inch ounces upon closure of the bolt, it is clear that the energy threshold of primer functioning should be safely above this figure to guard against accidental pre- mature firing. Considering that the "none-fire" criterion of the .223 primer is only about 6 inch ounces, it is somewhat surprising that premature firing has not been more frequent ...The threshold of energy, below which primers must not fire, must clearly be above 15 inch ounces for safe and satis- factory use in present AR-15 rifles.
Wm. C. Davis, Jr.. AR-15 Project Director The firing-pin-indent fixture., [was] used to obtain the depth
of indent made by [ten trials of] the firing pin when struck Rifle No. Rifle No. Indent Depth, Inch: 007237 007249
Average .0078 .0061 Maximum .0090 .0075 Minimum .0065 .0045
Firing Pin Energy, Ounces:
Average 11 7
Maximum 14 10
Minimum 8 4
Rifle No. Rifle No. Indent Depth, Inch: 007237 007249
Average .0234 .0220 Maximum .0245 .0230 Minimum .0225 .0210
Hammer-Blow Energy, Ounces:
Average 84 77
Maximum 89 82
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The TCC met at Springfield Armory on June 25 to discuss the results of the Frankford Arsenal primer sensitivity investi- gation, which had included a discussion of a theoretical primer which would all fail to fire at a force of 16 inch ounces but would all fire at 64. When it was learned that such a primer would produce an inadvertent fire probability in the AR-15 of only "1 in 10 million", a "coordinated Army staff position" plumped immediately for the 1 in 10 million risk factor, despite the fact that primers made to the required specifications did not actually exist.
A compromise of sorts was worked out on paper, and the two main suppliers of cartridges, Olin and Remington, were asked to bid on cartridges loaded with primers having 12 to 48 inch ounce none- and all-fire thresholds, to which Frankford had assigned an estimated 1 in 6,400 probability
of inadvertent fire in the AR-15. Neither contractor would even bid on the project, stating that trying to produce primers to such limits was too tricky in large volume, and would lead to very high lot-to-lot rejection rates. At a further ammu- nition meeting at Frankford early in September, the Arsenal staff nevertheless advised the T C C not to relax the 12 to 48 inch ounce limits, at the risk of an unacceptable probability of inadvertent fire in the AR-15. Remington estimated that they would have to reject 50% of such primers made, but gamely agreed to try if the Army would allow the primers to be accepted or rejected before being loaded, thus preventing the rejection of an entire lot of ammunition solely on the basis of faulty primers. Olin estimated they would reject two out of every three lots of primers made to such limits. Two weeks later, they revised that figure upwards, to 90%.
Down to the Crunch on the "One-Time Buy"
Meanwhile, with both the "slamfire" problem and the bolt closure debate still unresolved, the TCC was being forced into a compromise position due to time constrictions soon to be imposed by simple economics at Colt's. Not just another arsenal to be ordered around at will, Colt's was a private company with a normal, not to say desperate, concern for the "bottom line". As such, Colt's faced imminent financial ruin as a result of the government's double stranglehold of delays in domestic acquisition and embargo on foreign sales. The firm had already advised the Army that as soon as current obligations (notably the 1962 Air Force contract for 8,500 rifles) were fulfilled, they would shut down and dismantle the AR-15 assembly line in order to reassign both the men and machinery involved to other, more profitable tasks.
Finally, on October 25, in the face of continued indecision on the primer sensitivity and firing pin modifications, Defense Secretary McNamara sent a memo to Army Secretary Vance, relenting on his hitherto unbending order that all four services agree on "one rifle". Even at this eleventh hour, he obviously hoped that the Army would come to its senses over the bolt closure idea, which he had vigorously opposed:
138. With special primer development holding up the solution to the "slamfire" problem, Colt's and Springfield Armory undertook an examination of how to lighten or somehow restrain the AR-15's firing pin. Colt's "No. 2 Design" was at length chosen as the best approach.
Springfield Armory photo dated December 3, 1963
..Since the AR-15 line [at Colt's] now producing Air Force rifles must close unless immediate action is taken, you should initiate all planned procurement at once. To satisfy the disagreement about bolt closure, the require- ments of the Air Force should be procured without this modification. The Army may procure the rifle with the Colt designed manual bolt closure. In case your field tests,
to be completed by 20 December 1963, indicate a lack of need for the bolt closure modification, the Army is authorized to revise its order to the same design being procured for the Air Force. Likewise, a selection of the bolt and pin modification to insure against inadvertent fire can be made as late as one month from contract without signi- ficant effect on deliveries.
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