I also have been toying with the idea of a N frame carbine. I have built in the past a Luger Carbine in 9MM and two Buntline Specials one in .45LC and the other in .44 Magnum. All with 16 1/4 inch barrels just in case the ATF ruler is a little longer than mine. They all shoot pretty well. If I get a chance I'll take pictures and post later. I seen a K frame done in a collection in Claremont OK. Very well done and I have photos of that. Could you post a photo of the S&W gas gun shoulder stock so I know what I am looking for. I have a friend that's a major police supplier and I have him look for one for me. Thanks Frank Jr.