I don�t have the 243 HS compatator but have one for the 30-06. The 243 should be .4" and the 30-06 is .375". I think I should be close to use the smaller diameter comparator if I just compare differences. And here is what I found. From my single shot NEF, fired brass is .017" longer HS reading than the unfired-factory-loaded-ammo measurement (federal), FL sizing reduces this to .007" longer than the unfired factory reading. The FL sizing required much more force than I have become familiar with for my 30-06 (bolt action).

Also, a bullet does not slip into the case of a fired, not sized, case. I have not checked case wall thickness yet.

To me, this looks like my brass will not last long with FL sizing, I have a Lee Collet die that I want to use but so many people are warning of ejection problems from neck sizing with these NEF rifles.

What do you think of this situation? I know I have some more data to collect, like firing reloads, and trying different factory ammo.

I dont think that I would do any full-full length resizing. I would opt for some partial resizing and aim at a .002 diff from resized to fired comparator readings.

As far as a bullet not slipping in a fired case neck freely. I think it should just barely go. Better check all those dimensions closely. You may need to neck turn.

the ave neck thickness is .0145