Let's keep this simple. usually a 30 caliber cast bullet sized .310" will shoot just fine. I size all my cast .30 cal. bullets to .310 and they shot great in my 30-30s, a Marlin 336 with Micro-groove barrel and a Winchester m94, two M64s and a rather rare M54. They even shoot goot in a 14" T/C Contender. Look for a bullet like the Lyman #311291, a somewhat bluff round nose bullet. When you get some, stick the noze into the muzzle of the rifle. If it's a hait too big to where you have to push a bit that's OK. If is slides in snugly, that's good. If it's a loose sloppy fit accuracy with most likely be lousy. There is a good chance it will slightly more loose in the Marlin due to the shallower type of rifling unless you have a gun with the Ballard style rifling. If your gun will allow it, seat the bullet so it slightly engages the rifling. You don't want to jam it way the hell and gone into the rifling, but just enough so the bullet is centered into the barrel which will keep things a straight as possible. The more things are aligned, the more accurate the load will be.
Oh yes, before I forget. Clean that barrel as good as possible. You should try and get out every bit of copper fouling possible. It'll take a few shots from the ultra-clean barrel to foul it properly for good cast bullet results.
Paul B.
