It's a simple problem. There are two shell stops on either side of the magazine on the bottom of the loading port. One stops the shell initially and the other one stops the next shell in the magazine so that only one is ejected at one time. This is a timing problem and the second stop is letting loose when it isn't supposed to. I had somebody buy a used gun of mine with this problem. I took it back and gave him a refund. The problem might be that it wasn't cleaned well enough. The stops have to be removed completely and the gun thoroughly cleaned. If that doesn't work, either get new ones or contact a competent gunsmith to adjust them. I had to tweak the stop inward slightly so that it positively engaged every time. Had this problem with Ithaca 37's too. On the Mossberg, though, the length of the stop could also be a problem.
[This message has been edited by badgerarms (edited July 03, 2000).]
[This message has been edited by badgerarms (edited July 03, 2000).]