I have picked up a nice 12 bore rifle- Damascus re-proofed in jolly old for nitro. Right groove dia is .755, while left is .751. Now, this is twisted for conical, but have a ball mould on the way because it was affordable, in .755. I figure it will fit nicely due to the small bearing area. We will see. Now, I want to use this with conical. I have a source for a mould in the fosbery style, at .740 and 750 gr. Cherry already exists. My idea is to get one of those, and open up the driving bands to- uh- what? .753 or so? Also, the rear band would be easy, the front not so easy. Would I get by just opening the rear band??

So advise needed- what dia to open to, and will both bands be necessary? Guess I can experiment slowly, but educated guesses would be appreciated!

Thanks, Doug