I have had the Dillon 550b for around 7 months now. Have figured out quite a bit with the press since owning it. Have an annoying problem with the press. The center bolt on the shell plate after 4 or 5 rounds tightens up and I have to loosen it with my finger in order to keep things rolling. Don't know what else could be going on. I have thought about putting a lock washer on it but the press didn't come with one so I figured it doesn't need it. Are there any thoughts out there? I love the press and will live with the issue if there aren't any recommendations.