They are 7.62x39 brass casings. At first I thought maybe someone screwed up and fired them from a 7.62x51/ .308 Winchester chamber but after measuring them I cannot be so sure. The mouth measures .433 the .308 Winchester chamber would be .454 at that length. I can imagine someone was wildcatting but, I cannot see someone fireforming their brass and leaving it out there so I am at a loss.