As they have said above, all Model 53 say ".22 mag " on the barrel. The inserts are .22 rimfire. The factory would provide another cylinder ,at a price, for .22 rimfire. I know of others who have bored the inserts for .22 mag, but this was unsuccessful as the inserts split. I have had my extra cylinder bored out many years ago to .22 mag and that has worked out fine. It's a fine weapon.