I have a Stevens Model 77B in 16 gauge. I've had the gun for sometime now. It use to shoot fine until one day whilst shooting skeet the gun stoped "pumping". I cannot get it to rack. The slide lock release will not work either. The release seems to be engaged as there is not much play in it. I have taken it apart and tried to see what the problem is with no success. Any ideas? Any help would be much appreciated.