Semi wad cutter, for shooting targets, cuts a clean hole in paper. Without measurements, I agree, .38, used from the 1920's until today. Exact measurements in 100's of an inch would give an exact caliber. I think I can see rifling marks, if so it was fired and went a long way, because lack of damage means it was near terminal velocity when it landed. Back in the .60's I hand loaded a ton of them. Seemed like we would load all night and shoot all day. It was a good life.