I had this happen and will bet that your slide extension assembly is missing the buffer. When this happens, and you shoot a number of turkey loads, the slide extension itself, not the mag tube, will bend right in front of the forks that go into the receiver to cycle the action. Subtle, but enough to bind the gun. When you take off the fore stock the slide extension should freely move through the cycling range of motion. I bet you find the forks bind. Problem with this is that you will not be able to bend it back to shape; at least I wasn't able to. I found a new one at Ahlmans..... Wasn't cheap but they had one. Buy a new one and 5 or 6 buffers..... That and the bolt buffer are the Achille's heel of that gun. I had a few bolt buffers made out of that hard white plastic... still on the first one!! Good luck