That sounds reasonable . I was thinking the shims were used between the die and shell holder to make sure you still made firm contact while adjusting for case head space . As far as cost , for me the comp shell holders may be the best money spent to date on reloading components . That is , of the components you don't actually need . We all use all kinds of stuff we don't really need to reload . These less mandatory things just make things easier , faster , more precise etc . I have so many of these things that I use far less . Primer pocket uniformers , swager , concentricity gauge , cartridge gauges , powder measures , seater dies , crimp dies , standard dies , bushing dies , bushings , presses etc etc etc etc etc . Oh man If I could go back and start over I'd save SO MUCH money