What rifle were you firing the American Eagle ammo in?I used to run it through my old school AR15 A1 clone with a 1:12 twist 20" pencil barrel.
I never had a single issue with that exact ammo over many hundreds of rounds out of an AR.
15 out of a box of 20 is crazy. I would say possible but at those numbers, sounds like an issue with your firearm/firing pin, hammer spring etc.