Get a tooth pick and scrape out the undercut where the rim fits. You might be surprised at the crud you find. A few thousand rounds worth of gunk accumulated in there can cause problems. :(

Also, fine grains of tumbling media can get trapped in the cartridge rim and transfer itself into the shell holder during reloading. Visually note that each cartridge case is fully seated in the shell holder before running up the ram. The shell holder is such a small part that it can easily be taken for granted and receive little maintainence.

Get a tooth pick and scrape out the undercut where the rim fits. You might be surprised at the crud you find. A few thousand rounds worth of gunk accumulated in there can cause problems. :(

I do that on a routine basis, seems I'm always chewing on a toothpick when at the bench so it's pretty handy.