could a 300 win mag chambered barrel be rechambered for 300 H&H?

No. the H&H (even though it is longer) has a sharp taper and the WM is blown out. So the chamber would not clean up at all. Unless you want a unique 300 mag with a double shoulder in it called the .300 Bluefish.

Ha! What would the shank and 26" muzzle diameter need to be to rebore up to 375? i assume the muxxle could be trimmed back to get enough meat for the rebore? could the barrel still balance well?

No, won't work either; 300 shoulder is .477; 375 case at the same place is .448. Double shoulder thing again.
I know, I like to use old barrels but I do not like re-boring unless trying to restore a unique barrel whose outside configuration you like. Otherwise, get a new one.
Shank is no problem as the 375 pressures will be less than a 300. Muzzle; I like them bigger rather than smaller; I like .650 min with .750 better. No it would not balance well for me. It is more a matter of recoil than strength; discuss all this with a rebore guy.
But,, check the 375 taper too, as it might not clean up a 300 wm chamber either. I will check it later. soon. today.

interesting. i would hve thought a rebore to the 375 could take care of the whole thing.

You can probably get away with going from the .300 Win Mag to a .300 Weatherby Mag.

Easiest way I have found to determine if a barrel can rechamber and to what is Ammoguide.

http://ammoguide.com/cgi-bin/a...er.cgi?sn=BXTDvxtdLK

Usually is pretty accurate.

i see the rechamber is out but wondering about reboring. perhaps a rebore may be more feasible to a 338 or 9.3 caliber.

quote:

Originally posted by bluefish:
i see the rechamber is out but wondering about reboring. perhaps a rebore may be more feasible to a 338 or 9.3 caliber.

If your goal is to get a larger caliber magnum round, there is no reason you can't have your .300 WM rebored and the chamber enlarged to take an .300 WM case with an expended neck diameter and throat.

But why bother? You'd still have a wildcat for which there is no factory ammo available.

I've had .30-'06 barrels rebored and re-chambered to .358 Norma Mag which worked out well for me , but today I wouldn't bother doing that simple conversion either. There are too many good barrels around at inexpensive prices to bother.

Better, in my mind , would be to simply buy a used rifle made for the cartridge you want. Probably less money and less worries. And you could spend the left over loot "personalizing" your "new old" rifle.

Yes, What Alberta said.