I have run into the same issue with my daughters Plinkster. For the first year, it worked fine all the time. This summer when we took it out to use for 4H Shooting Sports, the problem started. It works fine for about 20-40 rounds, then the action gets harder and harder to work, eventually seizing up. I've tried it 2, 4, and 6 hours after seizing, and it was still stuck. If I then over night, or longer, I can once again work the action without an issue, until the next time I fire 20-40 rounds - then the problem repeats itself. This has happened at least three times. I have not yet called Mossberg support, but will try that. Anyone have a cause/remedy/prevention?