Or you could actually put a .22 sleeve into one of the barrels of an O/U shotgun, course you'd have to make sure you get the twist you want, if available. It's called an "einstecklauf", but they are fairly expensive. Shorter lengths are also made for the .22 rf models, which are a bit cheaper. Just thot I'd throw it out there for FYI -- I've got one in .22 mag about 12" long in the top right barrel of a drilling. Waidmannsheil, Dom.
Here's a pic of a full length, probably in caliber .222 or so, not fully installed yet, just showing how it goes in.
