I looked at the manual and tried to remove the shell plate because 1. I'm curious and 2. I think powder is jamming it up, and all I got was the know and metal ejectorThe shell plate is easy. unscrew the knurled nut in the middle, slip off the metal ejector arm and the O-ring, pull the plate off, put the new one and and re-assemble in reverse.
here's the manual
http://leeprecision.com/cgi-data/instruct/LM3231.pdf
From my sniper hide