It would help if you told us what kind of reloader you are using. I had a similar problem with my MEC. 600. It turned out to be a small piece of shot had gotten between the top of the bar and the chanel in which it is held. To cure it remove the bar and look for any small piece of shot. Check that the rubber gromets are still in the bottom of the caps, these help to keep the shot pellets from shearing as the bar is being slid. Thats what solved my problem I bet yours will be something similar. Another cause could be powder binding the same area. If you are using a fine ball powder MEC has a small brass shim washer which goes between the bar and the cap(under the rubber washer), the theroy is to stop the fine powder from getting on top of the bar. If there are small amounts of spilled powder on top of your loading bench as you reload this could be your problem.