Funky marks on primers?

[onesureshot]

I went shooting last week with a buddy that was using a POF piston rifle. He gave me a bunch of brass that he had fired that day. When I got home and was looking at them noticed the primers had a funky mark on them. As you can see in the pics, they have the normal dimple from the firing pin, but then there is a raised bump around it. I am guessing it is from the primer cup flowing back into the firing pin hole, but wanted to throw it out to get other input. I don't think it is a pressure issue, as the same ammo fired in his bolt action looks completely normal, and even the primers with the bump aren't flattened or anything like that.

Is this normal for piston ARs? Could this cause any problems? Or could this be indicative of something he needs to get checked out?

Thanks for any and all feedback.

 

[Hateca]

Re: Funky marks on primers?

It's common in all kinds of rifles. Could be caused by high pressure or just a little over size firing pin hole.

 

[deadly0311]

Re: Funky marks on primers?

that would be some cratering there if im not mistaken

 

[Hummer]

Re: Funky marks on primers?

Looks like reverse striker flow to me. It is because the striker spring doesn't give enough energy to the primer to sustain the indent while the pressure rises and falls.
Replace the striker spring with a Wolf spring (preferrably a heavier one) and this should disappear.
I just had same identical stuff on a Rem 7615. I replaced the hammer spring and it went away immediately.

 

[Rovieairto]

Re: Funky marks on primers?

Does it have a lightweight (Ti) firingpin?