that's why blank attachments illegal ones I think are ok. Firing pins are another thing all together. They are also made of some patented aluminum alloy, if I recall. If it breaks during firing, than its a hassle. But not as bad as cook off.
last time during NSF days, I got a dozen spare magazines and don't know what to do with them. I thought it is a waste giving them back to the armstroke so I kept on holding on to them until toward the end of my ORD when I decided to give the magazines to my junior