Yeah, Mike, they do work. I have Kreighoff and Walther inserts in the shotgun barrels of my two Savage/Valmet 2400 O/U combinations. The one with the .222 Remington rifle barrel has a .22 LR Walther insert in the shotgun barrel, and the one with a .308 barrel has a Kreighoff .22 WRM insert in its shotgun barrel.
I zeroed them for 50 yards at the same scope setting as the centerfires use at 100. Took a lot of fiddling, but it works well. Of course then our geniuses here in CA decided that you can only use "green"--unleaded--ammo down here, so I had to go over the same process with all four barrels.... I think I'm back to a good zero for all four now, many shots and lots of cleaning later.
CCI "Quiet Green" .22 LR ammo is next to silent in the shotgun barrel, the only ray of light in this costly process. Probably the first time a 12 guage barrel has functioned as a suppressor.
