12ga. I will likely send it back this fall. I had some trouble with it right away. Got it last year for Christmas from the wife. It arived with the cam over piece at the bottom of the ram broken and the wad arm broken. Came from Midway and I should have just sent it back to them, but I called RCBS. They shipped out the replacements right away. I also had a problem with the plastic guide fingers and the little clips that hold the shells on the shell holder. They have been great with this stuff, but I problebly should send it back for them to set up. I can't load the new style AA's w/o crushing the shells. I should just drop them another e-mail!