I have a Mossberg 535 ATS Field shotgun with a 3 1/2'' 12GA chamber. When I was shooting doubles in skeet today I missed the second target half the time. Not because I was missing the clay but because my second shot was falling out of the tube before I could cycle the action. It seems that the recoil of the first shot causes the second shell to come out of the tube. I think it may be a problem with the shell stop but I really don't know. Any ideas?