I'm sorry, I should have been more descriptive. The magazine stop isn't working in that it seems to be stuck in the detent groove, allowing the shells in the magazine to all squirt out while being loaded. If one is careful, it can still be loaded, and functions fine after that, but loading can be tricky.
Diss-assemble the magazine tube- remove the stop leaf spring and the hanger brackets, and of course the lock pin and the two set screws and the end cap-- remove the follower the metal cup) and the coil spring, clean thoroughly and check the tube ID for burrs or dents that might impede the tension of the coil spring against the follower- also check the threads of the magazine extension and also the threads of the tube- for dents, burrs, dings- and make sure when you re-assemble the gu you have the alignment arrows properly oriented-
