I also note there are variety of chamber adapters and not all are steel.
I have chamber adapters from Browning (Little Skeeters with a Browning package), Seminole ChamberMates, and GaugeMate (Silver). The ChamberMates and the GaugeMates are stainless steel, and the Browning (Skeeters) are aluminum. I don't have GaugeMate Golds but I understand they are also stainless with a gold finish. The GaugeMates and ChamberMates are no longer made and getting hard to find. I shot ChamberMate 12/20 adapters for the dove opener with old Kent Gamebore 2-1/2" black powder loads and the inserts functioned flawlessly, including the extractors. This was in an 1880's Lacey Birmingham hammer gun with "Fine London Laminated" barrels. I recently got, but have not yet used, a pair of Briley SideKicks for my Parker Bros G-Grade Damascus top lever hammer gun. The Brileys appear to be all aluminum and they will see the field next week. I recently looked around for new production chamber adapters and everything I could find (other than Brileys and Little Skeeters) looks like stainless and is oriented to preppers and plinkers. Nothing for birds or clays with extractors.
