Originally Posted by
DonH
I don't have all the experience I would like in this area but this is what I think.
First off, you need .002" neck clearance minimum. Then work back from there. You have to know chamber neck diameter or you are just guessing. Slug chamber neck with a soft .38/9mm bullet first.
Next, cast bullet diameter is usually .002" over groove diameter so if your groove .s .318" common practice would call for a .320" bullet.
Before going too deep into this project, I would beg, borrow or steal a .321" jacketed bullet and get it seated in one of your cases. Measure outside neck dia minus .001". Compare this dimension with the dia. of your chamber neck slug. This will tell you is a case with a .320" bullet will even chamber. If the assembled round has a neck only a few thou larger than chamber dia. You COULD reduce neck wall thickness by neck turning until an assembled cartridge has a neck dia. that allows that min. .002" neck clearance.
This ia all BEFORE you get to " will the pitted barrel shoot?". If all this is the case, you would have to hone a bullet sizing die to size, get a .321 mold (easy), get neck turning equipment and/or ream the chamber neck to fit. Or you could size .321" jacketed bullets to .318" and shoot it IF they chamber.
Or move on to another rifle.
Or maybe someone else has a better cast bullet solution, then I will learn something too!