Hmmmm....."floating firing pins"......
I remember when this type discussion would be centered around sensitive primers and military arms with floating firing pins, mainly the M1 with OPs worrying about slamfires.
New generation....plastic rather than wood, still with floating firing pins......do ARs slamfire?
Only if you leave your primers high.
First hand experience with that....and while I "normally" check for high primers.....it only takes one.
Embarrassing too....a friend and fellow reloader got a surprise, shooting my new (at the time) Remington R25... an AR10 7.62 clone. We were shooting at a target in the Southern Colorado outback, and he wanted to try the AR out. First shot went BoomBoom....a twofer!
He looked at me like, "what the hell?" We didn't shoot any more.....til I looked at the batch of 100 real close first....and yes I found one more proud primer in the lot.
What's more, I had used a uniformer on the old 67LC brass after swaging! Found out that I STILL shoulda watched, because that very old hard brass didn't always swage normally.....at least two times it sheared instead of swaged. That's to say it sheared that crimp, yeah, cut it off! A tiny sliver of brass was pushed into the bottom of the pocket, where it stayed even after using the Uniformer. How, Why?
Because it rotated in the bottom with the uniformer, keeping the uniformer from cutting anything.
I broke down the other round with the proud primer and found another sliver of brass in that cup. MORAL: even if you swage and uniform....check the cup bottom before you prime.....and at the very least check for High Primers even if you are SURE there couldn't be one.
Oh! BTW, they weren't sensitive Federal primers....CCI's (but not military CCI's). We shot the rest of the batch with zero problems....and eventually my friend quit flinching...