Hey, been there with the same gun. The issue (according to smith that does the majority of the warranty work for mossberg) is most often caused by the cartridge interrupter. Remove it and the cartridge stop, clean, oil and re assemble. Use a good oil like G96, or whatever you have. If this does not work, then you will have to get them to replace both of these small stamped steel parts. They have a 5 year warranty. If you don't know what these parts are or how to take it apart and clean and don't have your manual, go to mossberg.com - under customer service - then owners manuals. It is a bit of a pain, but I find that if I keep it really clean and lubed this problem goes away. Good luck!