My Uncle has a Knight Revolution that had the same problem (actually still does). It too is realted to the breech plug (although I say it is more just a junk gun). Knight told him to unscrew the breech plug a couple of turns as opposed to seating it at a proper depth. Now the gun fires, but he has one helluva time actually loading the disc. It was a jerry rigged fix and the gun is still crap in my opinion, also dangerous, but I won't go into those stories.