If it's for 30 cal, then I would use it. If you're pulling the bullets to make up Mexican Match hunting ammo and aren't going to use the fmj for anything special, I wouldn't worry about being a few thou one way or another. The collet should cover the range between .312 and .308.
I don't have a collet puller. I just use the kinetic hammer and reweigh my powder weights back in the case after the fact. More work, but I have time...