I'm still new to this and learning... I have a bunch of once fired (in my rifle) rem brass that I'm reloading. I was going to use a fl die to just bump the shoulder .001-.002 as recommended. Curious issue is that my once fired brass is on average actually .001-.002 shorter to datum line than a few loaded remington factory rounds that in using for comparison purposes. I am using a hornady headspace gauge, and am getting pretty repeatable measurements. When I use my redding premium FL sizing die, I can't even get it to touch the shoulder, even if over-camming with a bit of pressure. OAL of the case does not measurably grow after sizing either. So I say to myself "fine, if the the headspace is bumped back already, no sense in touching it". But this all seems very weird, and not in line with the reading I've done. I have not yet tried to chamber any of these, and will give it a shot tonight.