My marlin 1894 will feed cast 255gr. "Keith" style swc very well. Once and awhile you will run across a 1894 that will need minor tuning to feed SWC cast lead bullets. As for the dia. size, you will find that the best accuracy will be with bullets that have a .430 to .432 dia. You can order cast bullets from Beartooth Bullets and select your dia. size up to a .432 that works best in your rifle.
I would start by purchasing 100 bullets in both .431 and .432 dia. and find out which will give you the best accuracy. Most marlin barrels run slightly oversize and .429 bullets will not give the best accuracy. :
I would start by purchasing 100 bullets in both .431 and .432 dia. and find out which will give you the best accuracy. Most marlin barrels run slightly oversize and .429 bullets will not give the best accuracy. :