The ring was in part a function of the fact that the boltface around the firing pin orifice was greatly eroded from the hot gases. I don't still have that bolt. Threw it away years ago. The brass in my pic is brass I fired in 1997. Been sitting in a bucket until yesterday. Figured I'd snap a few pics before all the evidence was destroyed.
I went through several hundred pierced primers, several ruined bolts, and several ruined firing pins, in that gun before switching primers.
Yes, there was a lot of primer metal discovered in the mechanism after a day at the range.
I suppose we can debate until we are blue-in-the-face over whether the hammer spring is too weak.
In my opinion, the load was quite hot (run my numbers through Quickload - you will see), and the thin primer metal was the weak link. I could have had the hammer spring of THOR, and I'm quite certain the result would have been the same. Many other of my teammates at the time were using the same, or similar loads, in rifles with different triggers.
In each instance - same result - until we all figured out that we needed to use magnum primers to end the problems we were causing.
Remember too, 1997 was right about the time the mouseguns were overtaking the M14 in service rifle honors. We all thought we had to hot-load (overload?) .223 ammo to be competitive. I have since learned that ragged-edge loads are not generally necessary to achieve success in high power rifle competition.