Sorry if this has been discussed, but I could not find an answer that suited me. I was cleaning my franken-M4gery built with a CMMG MPI BCG. It has performed well for about a thousand rounds, and I was cleaning it today. When I opened the bolt, this O-ring popped out. I cannot figure out where it could have possibly come from, or if it's even needed. Any thoughts?
It is pretty beaten up and flattened out. Could it be the O-ring feom the extractor spring?
https://sphotos-b.xx.fbcdn.net/hphot...02818958_n.jpg

