I have a Howa heavy barrelled 223.
It has been and still is a superbly accurate rifle.
Last weekend, I used new Lapua cases and measured and weighed 3 cases and bullets for a number of different bullet makes.
I used Ramshot X-terminator powder and CCI BR4 primers. Seating depth 2.245". 100 yard range.
The results were superb, 0.695".0.400",0.767" and 0.670" well pleased.
Having some spare time thought I would dig out my comparator and experiment more.

Problem on every bullet tried in that the bullets were just hanging out of the modified case, followed the procedure exactly in that I'm sure that I was not too heavy forwarding the bullet in the comparator.

So would I believe that I'm correct in assuming that the 'throat' has been shot out with about 16 years of use?
I have the same 'problem' with my 6.5 Swede 1917 vintage, comparator no good on that, but found a C.O.L which it likes and still excellent accuracy.
The 223 C.O.L is 2.260", I've always loaded to 2.245" and that depth has and still works, I used the comparator as bullets and cases vary, and getting to 2.245" on every round was a pain, so thought I could tighten up even more and stop the fiddling round loading to C.O.L.