I know its not a double already, but I can't find the answer anywhere on the internet. I found an old Winchester Mdl 12 20 gauge with a solid rib and 25 inch barrel. I have never heard of one with this length. Before you ask, yes I measured it correctly. The solid rib tapers up to the end of the barrel which looks correct also. Full choke. Feel free to email me at brdslayr@clearwire.net to let me know your thoughts or facts so as not to tie up this fine site. Thanks JW