Bore slugging, or determining the dimensions of the bore of a rifle, comes up a lot, here's how:
Get some soft lead egg sinkers, make sure they're not the non-lead kind, they're too hard. Follow the basic directions in the link below. I like to pancake the sinker between dowels, you get a much nicer slug than one that you just push thru the bore, do one near the muzzle and another near the throat, push it out the near end, that way you'll know how much bigger it is at the muzzle than at the other end, it will likely be about .0005" tighter at the chamber end.
Tim
http://7.62x54r.net/MosinID/MosinSlug.htmEgg Sinker Size:
Size 10
For use in .270, 7mm, and .30 Calibers
Size 9
For use in .338, .348, 38/.357, and 35 Calibers
Size 8
For use in .41, .44, .45, and .475 Calibers.