Trying to fix up my 870 express 12 gauge. One of the problems is the magazine spring collapses on itself sometimes and it won't feed shells. You have to take it apart to fix it. Can't figure out what would cause this. I know it's a common problem because two friends had the same issue. Any ideas? Maybe just a new spring? Also sometimes it won't eject shells right. They will stick and jam when the new shells pops in. The extractor is visibly worn so I'm guessing that's the problem.