Since that round headspaces off the case mouth, it shouldn't be too much smaller than the SAAMI spec, which is 0.473 in diameter at the mouth of the case. Sometimes when crimping rimless rounds like this (incl 9mm, .380, etc), getting them pretty is also getting them under spec. It's not uncommon to get under spec a little bit. Even a lot of factory ammo is. But if you go too far you're asking for trouble.
EDIT: Looking above at BYJ04's post, it seems even the loading books don't have a standard size, but we're all in the same safe range.