I bought a Nova last year for waterfowl hunting. Worked great no problems at all. Must of put over 3000 shells through the gun since and no problems until last week. about 50% of the time when i shoot and pump the shell ejects but the next shell does not pop down. It acts as if i am pressing the button on the pump but i am not. I have to sit there and slam the pump down a few times for it to work. I have missed alot of birds due to this. The gun gets cleaned everytime i use it so i know its not dirty. Any thoughts?