I am going to make a couple of assumptions on this one because it has escaped identification for years. I am going to assume it is American because of the REMINGTON UMC No.3 "shotshell" in the base. I am also going to assume it is a mortar type projectile because of the "shotshell" and the side openings in the tail section. From there, the assumptions stop and confusion begins. The body is a cast steel with four elongated machined surfaces for bore-riding. The copper band is of a slightly smaller diameter than the major diameter of the body. It appears to be more of an expanding gas check than a rotating band. There is a flat circular "plug" in the nose. There are four long fins cast as part of the tail section. Inside the base is a tan-bodied "shotshell", which I assume (their I go again) is the ignition cartridge. The overall length is about 11 3/8 inches. The copper band is about 5/8 inch. It is 3 inches in diameter. There are no markings at all and no apparent break in the body/tail section where it would come apart. If there are any hidden breaks, they are corroded closed over the years beause I have tried to separate various sections. I have exhausted every reference and museum in the US I could think of and have zero information on it. I thought I would offer up the challenge to this knowledgeable group.