A perfect bore should be around .311" groove diameter. But... most are far from perfect. You'll find commie bores that range from .310" to .318" (8mm
). Most are in the .312" to .315" range.
But... if you're shooting jacketed bullets, it doesn't really matter. The grooves are quite deep in Mosins, and often even work well with .308" bullets. I wouldn't worry about bore diameter, unless you want to shoot lead bullets.
TMW -
What do you mean by "decent groups" ?
3 inches? 5 inches? Minute-of-barn?