Holy shxx! That (photo 1) looks to me like........... Are you putting TNT in your reloads? The pressure in the case is forcing the primers back into the striker hole. Is the gun a standard UKicon made L4 or a US re-weld/semi auto? While I don't know much about the US rewelds it LOOKS like the primer has blown right into the striker hole, driven the striker right back against its stop, THEN the primer has tried to extend further into the hole, wrapping itself around the striker to the point of almost exceeding the extent of its elasticity ALMOST ready to pop.

Never seen anything like it in my life and I've seen one or two Brens and L4's. You MUST compare and measure the striker hole in the breech block with a know good one. Is yours enlarged? It will be before long!

Just my view as a bit part onlooker.......