In some of Dan Lefever's writings, one of his early catalogs as I recall, he mentioned that when he converted muzzle loaders to breech loaders he bored out the threads for the breech plugs & sleeved them for the new chamber, which according to him resulted in greater strength than cutting off the threaded portion as that would have left the chambers thinner. I don't know if he was the "Pioneer" of this "chamber sleeving" or not, but seriously doubt he had anything to do with the British Proof House accepting it.
