where to buy 30-30 cast boolits?

[Ranch Dog]

0.311 .......sounds more like bullets for 303BR or 7.62 x 54R.
The nominal diameter for 30-30 bullets is 0.308 "
Running over diameter lead bullets could lead a barrel real quick.
I'm guessing with lead bullets they'd need to be a little over nominal diameter to give the rifling a good uniform "bite" on the bullet in order to impart the very fast rotation which is necessary for flight stability .......especially the heavier bullets.
And lead has a lower coefficient of friction against barrel steel than the copper or gilding metal of the jacketed or new mono-metal bullets.

Actually, an over diameter lead bullet will prevent leading. Many designs, like my original TLC311-165-RF, use the excessive diameter (.311) to fill the throat. That seal, where ignition is taking place, is what prevents the leading. This statement is very true with pre-2010 Marlins. Marlin used large throats to allow smooth chambering. This is also why slugging a barrel tells very little about what the bullet needs are. The only way to truly tell is with a chamber cast or impression.