Found half of what I'm looking for... per 'bug' earlier post: [search 'hotshot']
"Recently, I reamed an extra choke (for my .44 bbl) so there was no longer any rifling. What I wound up with was an 8" bbl with a .429 groove, a 3/4" comp chamber of about .480 (with two gas ports on either side of the front sight), and a smoothbore "barrel extension" about 1 1/4" long with an ID of about .440.
I was hoping this would work like a compensator, and... IT Does! Muzzle flip went from almost 90 degrees to about 45, and felt recoil was reduced perceptibly. This is totally subjective, but two other friends said they also felt a difference. This was tested with a hot-loaded 240 gr hard-cast, and a 300gr jhp. Groups remained comparable with the extension on or off. "