Have tried scouring the interwebz all over for a clear-cut answer to this question, and I can't seem to find anything as of yet.
Does anyone know where the dimensions differ, and exactly by how much?
Just picked up a NOS unfinished ER Shaw barrel, but the guy couldn't tell me if it was an AR-10 or LR-308 extension that was torqued onto there; there is no indexing pin present, so I guess I could try to pull it off and exchange it for an LR-308 extension if in fact it doesn't have one, but I wouldn't know how or where to measure it...