Carbon in the necks will affect bullet release and bullet tension and maybe even concentricity. I agree that these are two different forces that affect cartridge reloading activities. More so in reloading for long range competition to the point I have turned to a seating force guage and the use of expansion mandrels. Over the years(40) I've shot .261", .262", and .263 necks in the 6PPC. The .262" is what I've settled on or a neck wall of .0085". Jim excuse me for using your post to answer this question from Jeff.I am curious as to your thoughts on carbon in the necks affeting neck tension after 5 firings. I often wonder about neck to bullet friction as opposed to neck tension. In my mind two seperate items but not seperated in the numbers we get usung a force guage.I often think because all my chambers feature a .262 neck it helps in consistent tension as opposed to thicker neck walls, but not sure that is fact.