Originally Posted by bigswede358
What does the barrel diameter need to be to make a 9.3x62?
Originally Posted by dennisinaz
35 Whelen is as big as i can go.
.575" muzzle

Hey bigswede358, The general number that I've seen recommended for a rebore is an extra .125 on either side of the bore for the larger calibers. So in dennisinaz's example above:

.575 - .35 = .225 (muzzle diameter - caliber = remainder on both sides of the bore)
.225 / 2 = .1125" remaining on each side of the bore.
He's a little bit below the "recommended" .125 thickness on either side but it's up to the person doing the rebore to decide the threshold they're willing to tolerate.

Another way to look at dennisinaz's situation is to calculate:

.575 muzzle - .250 recommended thickness (.125 * 2) = .325 maximum ideal caliber rebore for this barrel based on general recommendations. So a .338 or a .35 might depend on whether the person doing the rebore thinks that's advisable.

In your case:

9.3 / 25. 4 = .366 (mm / mm per inch = caliber)
.366 + (.125 * 2) = .616" ideal muzzle diameter (caliber + 2x the recommended barrel thickness).

So you need 15.6 mm or a little less than 5/8" (.625") to have the recommended .616" muzzle diameter.