Re: RCBS Headspace Mic?
If it's what I'm thinking, You screw the top part on a fired case, make a note which line it lines up on, lube and run the case through your sizer, measure again and see how many lines it screws down to compared with the first. Screw your die down till the case chambers like a virgin round, usually two lines, your shoulder bump is now finished.
I'm not very good a explaining on paper and probably have you totally confused...anybody else??