You're correct, good point. I've personally seen this with .223 reloads using Winchester primers in the AR15.
This may be old news, but at one time the combination of the AR15 hammer force and firing pin striking the softer cup on the Winchester small rifle primers was a recipe for problems. Shooting NRA Service Rifle matches with the AR15, I had pretty regular primer punctures, with soot evident on the primer, a little extra puff of smoke from the ejection port (at least I thought so...), and very sharp etching on the primer tip. More etching made the primer tip so sharp that it would puncture any primer, so I bought firing pins in multiples for a while.
The cure, in my case, was using CCI primers. As I said, that was some years ago, Winchester may have made a change to the primer cup material.
AR primers are different than regular rifle primers. If you don't use AR primers you can get slam fires as the primer is too soft.
So why is the brand of ammo not listed in the original post?