The 2.5 inch chambers are fine, since I will be loading brass Magtech 2.5 inch cases with BP only. Love blowing smoke - out of gun barrels, that is! The Greener linked above caught my eye. I guess being a fan of the movie Big Jake, Jacob Macandeles (sp?) was happy that his "Greeners" had been brought along. Does that seem a solid gun? Not in really collectable condition, perhaps. What about the asking price? Reasonable.
Now the Belgian sxs seems very solid and the proofs indicate that it has nitro as well as black powder proofs. You guys just had to make me dig for the information, didn't you? ;-) Thanks. I love doing gun research, especially on subjects I know little about.
And then there is this Parker Bros. Underlifter. Love those patent dates. No proofs in the auction. Who knows about these guns? I know, I know. Lots of questions, but now I am developing a general curiosity about these beasts.
http://www.gunbroker.com/Auction/ViewItem.asp?Item=83692461 
