I always dry test my guns after cleaning by cycling snap caps through them. At the very least it lets me know I put the gun back together correctly BUT I have neglected to test each mag after cleaning. Tonight I wanted to check out something on my TCP so I removed the mag and then cycled out the round in the chamber. Once I was done doing what I wanted I grabbed a mag (I had three sitting on my desk), placed it in the gun and cycled to place a round in the chamber. The slide wouldn't move. It had me confused so tried a different mag. It worked fine. In fact two of the three mags worked fine. The third one wouldn't seat well enough to feed a round. Still have no idea what the actual problem was but after I dissembled it and reassembled it, it worked fine. Long story short - not only check out your gun after cleaning but also check out each mag.