While examining a rifle bore after cleaning I noticed flattened globs of lead stuck in the neck area of the chamber. Maybe 50% coverage. Nothing in the shoulder area of the chamber. Factory chamber with .006" clearance for ammunition used. Low pressure load in 223 (1,500 fps with 85 grain 25:1 gas checked bullet).
Came out fairly easily by twisting a 30 cal. bronze brush. Always wondered what the chamber brush was good for that I carried in the butt of my M-1. Is there a similar brush for the M-16?
I do brush out the chamber once in a while so I assume it has been there before. Anybody else have this? What causes it? Can it be avoided? Should we care? The last string of groups before cleaning averaged smaller than usual so apparently wasn't hurting accuracy much.
It was making my chamber closer to a tight necked chamber but doubt that it was having the same accuracy improvement as a real tight neck chamber.