Most of my rifles I just shoot fireformed cases with no sizing, but I when I do size cases I always use very little neck tension. Typically I anneal the cases well, then I'll size with the sizer die backed out 3 turns. Then I use custom expander plugs to expand the case mouth to either 0.001" under the bullet diameter, or right at bullet diameter. in my 45-90fof instance, I have a slip fit load with a .459 bullet, and a 0.001" neck tension load with a .458" bullet. In my 45-100 I expand to 0.458" using a 0.458 bullet. I would use skip fit in that gun, but a fireformed case won't accept a .459" bullet, and a .458" isn't quite snug enough. In my 40-65's they always shot best with no sizing.