This is something I should have bothered to learn before I bought one. But I didn't know what I didn't know, ya know?. I don't reload so as long as 7mm Mauser is safe to shoot it's not a huge deal. I saw one on GB that was in a 7x57mm black powder cartridge but the rear sight ladder was way taller. When I told the LGS it was coming in he asked if it was 7x57 mauser or 7x57 rimmed, which I has never even heard of. By the looks of the rear sight it looks to be fairly flat shooting so I'm guessing it's 7mm Mauser or the closest thing to it.