Buy that mold and do not look back. There is a Marlin Forum that discusses the different rifling and which cast bullets shoot better in each type of rifling. All you need to do is slug your bore. Go to the Marlin Forum and those guys will help you out. No need to buy the wrong mold. You can also find the information you want on the CastBoolits forum. I use a RCBS 170 grain mold for my 30-30's. But they are Winchesters. My Marlin's are 44 magnums. Tom.