Rebarreling a M70 to .375 H&H. What is the minimum outside barrel diameter for a .375. Looks like most use a #4 contour with a .675 muzzle.

I believe you already have your answer , # 4 or #5 contour

There are no standard contour dimensions between barrel makers. Each maker's contour is different.

Look at muzzle dia. at actual finished length and dia. about 8" in front of receiver. Generally you will want a wall thickness of .150 on each side for the bigger bores so .675 is good finished muzzle dia.

You asked for minimum. Well, minimum wall for 375H&H at 23" or so could be as little as .110 for .595" which is pretty light but safe for that ctg.

Thanks.

Reread my post due to edits.

Just curious... what type of rifle are you building? Is there a reason you want it to be a light barrel profile?

Planning some future bear hunts. The CZ 550 .375 I have weighs a ton with a .675 muzzle diameter. Just wondering if I can put together something not so heavy.

There are lots of things on the CZ that are adding lots of weight besides the contour of the barrel

People nowadays aren't as strong as they are used too be back in the day.

you are stupid. the ONLY reason for a heavy .375 is if you are scared of recoil.

I hunted with a CZ .375 for 2 years now, and I have come to believe that a .375HH with scope, sling, and ammo in the belly should ideally weigh just under 8#s. They don't recoil nearly as bad as everyone who has never shot says they do.

Agreed. A 375 about 7.5-8.5 is perfect as long as it balances good. Even though I hunted with one that weighed 9.5 for a number of years.