I don't undersize bullets, at least not since the first couple times sizing them. I have a maximum force that I want a bullet to load, which is what I'm currently sizing bullets to and that is 30#.
I have minimum size, which has changed over the past couple years which is now 15#.
Where you're loading by feel using diameter, I'm loading by actual force to load, using a force gauge.
Just an FYI on loading a bullet in a clean bore at 30#........... After the first round, loading a fouled barrel is HARD and takes two hands and a STRONG range rod.