I'll second what Bramble suggested, have a look at Lothar Walther barrels and profiles.

I used a pair of the said Lothar Walther barrels when I built my first double, a 9,3x74. They have a muzzle diameter of .531". I made the action and all though, and didn't use a shotgun action. The rifle balances beautifully, with the weight concentrated between the hands, and it weighs in at a delightful 8 lbs neat. It is a joy to carry.

If it helps, I posted this article about it here a little while ago

The Walther barrels on my 9.3 double shoot well too. Individual barrel groups of three shots into 1 inch at 75 yards over open express sights are common. Composite groups of 6 shots (three right lefts) at that range hover around the 1-3/4 to 2 inch mark when I can see the target clearly - my eyes are not as sharp as they used to be

Go for Walther barrels if you can, you won't be sorry. Ready made to the right profile and weight, and good shooters too!

Best

Alex

alexbeer.com