This is the most important part on the Case Feeder slider setup. You can see it captures the rim of the case, it also has a channel for the primer to move in if there is any primer flow around the firing pin. This is common on brass fired out of a Glock. With out it your just trying to push a case that doesn't sit flat on the subplate into the shell holder. Sometimes it will work, occasionally you will have issues. Hornady simply does not have this part. And on top of it all your moving the case over the spring which is not flat and aggravates the issue.