saw a damaged breachblock today

I have had some experience with the firing pin retainer stripping out the back of the breach block. This was with Gunparts 16" Barrels which had excessive headspace. The fired case moves backward and the firing pin punctures the primer. Escaped gas pushes the pin assembly backward with enough force to strip the retainer out of the breech block. The fluted firing pin is supposed to prevent this. The stripped breach block can be fixed---not much fun though.