Bill, the last set of barrels that I fit to one of my hammer guns was from a Field Grade hammerless. The extension rib was doing exactly like yours. If you have a set that fits, compare the two extension ribs for length. I did compare them and the Field Grade extension rib was longer so I filed it and tried it, I did this quite a few times to make sure I didn't take too much off. I did get it to fit and now this makes this hammer gun a 3 barrel set. The last set of barrels are 32" and have .040 and .041 constriction. I only use it for trap shooting.