I have two Winchester 94 BB's that have a real problem. Sometimes, the cartridge in the tube slips out before it should, leaving it underneath the lifter and jamming the gun. The .356 does this quite often, and if you work the lever to chamber a round, then work the lever slowly back and forth without actually closing it, it'll always do it. The .444 has only done it once, but at the worst possible time, when I needed a quick follow up shot. My .307 and .375 have never done this, and cannot be made to do it even deliberatly. I believe it is the cartridge stop at fault, but how do I fix that? Are they interchangeble between calibers, or calibre specific. I've tried to take them out, been having some trouble though. Any advice in this matter would be great. Thanks.