Somehow this went from 12/15 martini to 12 Remington pump. Martini also had a mod 12.
I agree with Fox. Cash has always worked best for me. I would put serious thought into turning the 12/15 into a hornet get a mold Lyman 225438 and the stuff that goes with it. and you wont have to worry wether you will run out of 22s to shoot.