I'm using Lee dies until I can get the gist of what I'm doing. I'll pick up a headspace gauge later this month.
Just make sure you've gotten all the slack out of the press before you give up on the sizing die. All the way at the bottom of the stroke turn the die down until it is hard against the shellplate, raise the head, turn it down 1/4 turn, make sure there is zero slack in the system. That handle should be rock solid at the bottom stop with no play from the plate to the die. Then try sizing a case that currently is not chambering. If the case goes into the chamber farther than before, you're dealing with headspace not a base sizing issue. If you can't correct it, send the casings to me and I'll run them across my roll-sizer for you. That will bring the bases back within spec, it's cheating but it makes sizing sooo much easier on 308.