a very wise reloader told me the other day that when he measures the actual chamber on his rifles he says it will surprise you how much trim length you actually have to work with. so much so his case trimmer gathers dust. my first response was how in the world do you measure that without a chamber cast. he recommended these inserts that sinclair sells. they stick in a case and allow you to measure that dimension. he also said and I agree that unless your a benchrest shooter ie as in shooting groups in the .1's or .2's you will never see a difference in trim length.