All paint is different. Yesterday, I used some FS paint which was coming out at .675 (actually smaller but that was my smallest bore!). Depends on paint manufacturers, and then it can change from batch to batch.Or is there a certain size i can buy and just use no matter what paint i use?
I think Diablo Heat is bigg-ish though.
A full barrel kit is ideal, but if you only get one with a few backs, I'd make it:
.681
.685
.689
.693
Around about those sizes so you'd either underbore a bit or overbore a bit...