Thread: neck resizing setup

I'm reloading 243.
Hornady necksizing & depriming die. Lee Challenger press.
The brass has only been fired once, from new factory rounds, in my rifle.
Remington 700 rifle.

I have set up the resizing to stop at the end of the neck where it meets the start of the shoulder. After resizing I have put each empty cartridge into the rifle and confirmed the bolt closes and opens easily. Some are smooth. Some are not, requiring a bit more force to unlock the lugs in the rifle.

Why is this?

Some rounds when fully loaded are harder to close the bolt than others. The COAL varies only by 3-5 thou only.

Why is this?