I'm going strictly by memory here. Allegheney Rifle works used heavy Douglas barrels purchased in quantity, chopped an inch or two off the muzzle, and swamped them thus satisfying a need at the time. All 1 turn in 66 in. Late 70's. This didn't last long as Paris and then Getz who replaced Paris, picked up the demand. Douglas itself began selling swamped barrels shortly thereafter. And did so until it's withdrawl from the market.
Don Getz, I'm sure , will have a better answer if I'm wrong as he was part of all this.