Then you are talking about failure to extract ?
If the empty case is not being pulled completely out of the chamber, the first thing to look at is cleaning and polishing the chamber.
Follow this by checking the extractors for damage and proper tension.
If the case is being pulled from the chamber but drops into the action rather than ejecting from the gun through the port, then you have an ejection problem. This can be caused by the extractors as well, if they are damaged or the tension is so loose they will not hold the empty to the face of the bolt during its full rearward travel.
At the rearward part of the travel the base of the shell is suppose to make contact with the the ejector (this is a small plunger assy that is screwed onto the left inside of the receiver on your shotgun). The ejector would then break the empty free from the jaws of the extractor and toss it out of the ejection port.