I started casting for 38 special because I had been using commercial .358 lead fodder and knew that size would work. My next effort will be casting for a 35 Rem Marlin. Since I have only every shot factory jacketed in this rifle, I have no idea what the bullets should be sized to. So as I understand things, I need to slug the barrel and then size to the diameter of the grooves. How do I do this without messing up my rifle? I recently read that a .375 muzzleloading ball may be involved.