I'm learning more. My next move is to have the check remover from one of the molds I have. It's bound to make the bullet shorted and weight less. Should be interesting..
If you want to remove the GC shank without making the bullet weigh less, you don't have to mill the top of the mould off, if that's what you mean by making the bullet shorter. I've removed the GC shank from a few 35 cal moulds and one 30 cal mould with a chucking reamer. @Ben has posted on it a few times here and I think I remember him using a twist drill.