I have a set of the Briley chamber inserts, the Sidekicks for shooting 20 gauge in 12 I would sell. I only have the inserts, not the knock-out tool. I'd sell them for $155 shipped. They worked pretty well, but I got a 20 gauge barrel for my 12, so don't need them anymore. Above should be a web link to see what they are like.
not going to be easy finding a 20 with a release
I have a beautiful as new Browning XS Sporting 20ga..30" barrels, very nice wood,..with either 5 or 6 extended Briley chokes in new Browning hardcase...would be easy to have a release installed...$1950 plus shipping to your ffl