What I am asking is: If you had, say, a 30-06 that you wanted rebored to .35 Whelen what muzzle diameter would you need to start with? Could any standard 22 in. bbl '06 be rebored? Any ideas? Sean

Sean,
The "rule of thumb" is approximately 0.150" of barrel per side, in addition to the groove diameter. .308 + .300 = .608
.358 + .300 = .658
This is just a general way to think about this. Some makers go skinnier.
Bill

I'd just like to re-iterate, unless the barrel is special, ie has a quarter rib and barrel band attachments, or is an octagon, you will be $ ahead just getting a new barrel, not to mention get better results. For $300-400 you can get a pac nor barrel fit to your gun, the re-bore and chamber will cost at least this much, will take 1year or more, and likely won't result in as good a barrel.

Paul,

See the thread below "cut-rifle re-bore", it has a pretty good discussion.

Bill