There are a couple of books that I would recommend that could assist you. They are not painfully expensive, and both cover barrel regulation very well.
Building Double Rifles on Shotgun Actions 2nd Edition by W. Ellis Brown 55$ + 13 S&H

Shooting the British Double Rifle by Graeme Wright. This is a modern classic on doubles and their foibles. Check Amazon.com double rifle books. These two books and others are there.

Calpappus.com and NitroExpress.com are two interesting websites that may help.

Hornady sells ammo, brass, and bullets for this caliber. Nosler, and Woodleigh make good bullets for this caliber as well. Wolverine supplies in Manitoba sell Wooleigh's, and they also know a lot about doubles. They also sell and recommend Graeme Wright's tome on the double rifle.

Lastly; John Barsness recommends 65 grains of H-4350 with a 286 grain Nosler as his go to load for doubles in this caliber. Norma's website can provide you with data for this cartridge too.

Good luck and kind regards.