My remington 870 express is having problems extracting shells after firing. It happens approximately 3-5 times in one box of 25rnds. I will fire the round and attempt to pump it and the round will not budge. The only way i can get the empty shell out of the chamber is to slam the butt of the weapon on the ground while holding the forearm. I am a large guy 6'1 230 lbs with plenty of strength. Any help would be appreciated