Standard SR primers vs match/magnum/military

[SDW]

Any AR platform will allow the firing pin to hit the primer upon chambering a round & leave a witness mark on the primer, since the platforms do NOT have a firing pin rebound spring in the design.
It is not a primer selection/choice issue
ArmaLite AR-10's have a firing pin rebound spring incorporated in the design to prevent the issue.

I've run 10's of thousands of Federal 210's thru M1A's,M1Garands,AR chamberings, Bolt rifles shooting NRA OTC & LR Comps w/o a single primer issue.

I think the idea is, and this is probably obvious, some primers withstand that 'tap' better than others due to their cup thickness, and not go bang unintendedly. I guess in theory, anything with a 0.025" cup thickness can handle many repeated FP taps without any kind of worry.

I also read that if switching to CCI-400 primers from say, WSR primers, you should reduced the load a little. Interesting.

I don't know if it's just internet rumor, but supposedly (i.e., I'd read somewhere) that CCI does not recommend the #400s be used in an AR-15. Use them only in bolt guns, M1 Carbine, .22 Hornet, and so on. Having said that, I'm the OP here and I've fired at least a couple hundred #400 primed rounds so far and not had a problem. But I also don't make a habit of chambering and ejecting ammunition, then using it later. Once it's in the chamber, I use it.