During the development of the M16, field testing revealed an unexpected tendency to slam fire, that is, for the cartridge being chambered to discharge without the trigger having been pulled. Needless to say, this created much wailing and gnashing of teeth in the Technical Coordinating Committee. Since Secretary McNamara had been led to believe that the M16 was a fully developed weapon system, the fault had to lie with the ammunition.
Thus the Remington executive was brought forth and mightly chastised for the high crime and misdemeanor, "high primers." When the Remington man revealed that examination of tens of thousands of cartridges revealed no high primers, and that were the fault to be with the primer height one would expect out-of-battery fires rather than slam fires, he was told, "never mind."
Then Springfield Armory did a kinetic analysis and Lo! The firing pin inertial energy was 10 inch pounds! And the specified "no fire" energy level for the primer was 6 inch pounds! And the multitude stood in wonder, wondering why the d*mn thing didn't slam fire every time!
But, the M16 was a fully developed weapon system, so the primer, it must be changed! Only after a yield analysis revealed a potential 90% scrap rate with the new spec, was that avenue abandoned.
And in the end, Colt lightened the firing pin, and all was well again. Until Ball Powder, but that is another story.
Oh, and in 1941 Springfield Armory lightened the M1 Rifle firing pin. That couldn't have been to reduce slam fires, could it?
Some folks never learn.
And that's the rest of the story.
PS: The story of the M16 firing pin, the .223's primer hardness, et.al., can be found in Stevens & Ezell's "The Black Rifle":
Slam Fire: the M16 Story
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