I bought a new 870 express a couple years ago new, and since I started shooting, quite often the slide will stay 'stuck' in the locked position for a few seconds after the shot has fired. Either slamming the butt on the ground or waiting for 3-6 seconds will free it enough to pump to the rear. An army gunsmith filed a little burr out of the frame where the extractor passes through, but that's the only thing we could find. Has anyone encountered this or know how to fix this? I love the 870 and have used them in my past 2 jobs, but I hate not being able to depend on a second shot. Thanks.