You're kidding, right?

It doesn't matter how thin the ferrule is, so long as it has sufficient thickness at the front of the monobloc, and that is dictated by the taper on the original shotgun-barrels. Remember that the primary receptacle is a thin brass case, which is supported by the chamber wall. ("Wow, look how thin the wall on the case is..."). The Greener conversion has ended up with better than 1/4-inch chamber walls at the breech all-up. Personally I reckon that's plenty for the safe discharge of an 8-ton cartridge.

The finished weight of the gun is 10 1/2 lbs. Nothing else to reduce recoil except time-honoured British design (!) ...modified a bit! It's very comfortable to shoot.