I had a .22LR over 20 gauge model, 50 years ago, and the .22 barrel was insanely accurate, if you could master the horrible trigger. I occasionally stuck a cheap rimfire scope on the top barrel (grooved for tip-off mounts). I think that a .22 barrel full length brazed to a shotgun barrel (which would really dampen harmonics), along with a scope directly attached to the barrel, made for a very accurate setup.
