Ted-

That's why the Good Lord gave us the bullet sizing die!
I prefer a mould that throws a bullet somewhat oversize, in that no matter what alloy is used, they can all be put through a simple die for a slight swage to exact size.

I'm talking just a very few thou here.
Also, when designing a mould, especially via M.M. software (again, the software can be a little tricky), make sure there's ample grease groove depth, with room for the driving bands to upset into plus a margin, and to accommodate enough bullet lube to do the job.

Cheers
Tinker