In factory ammo, the shoulder never makes contact with the chamber - and the ammo headspaces off the rim. When one is not using "factory dies", but rather neck dies, one can allow the shoulder to blow fully forward to the point it will contact the chamber. When the brass is fully blown forward, I find that setting the shoulder back only .005" basically "overrides" the somewhat "loose" headspacing on the rim (at least in my chambers. The effect is much better accuracy and less trimming required thereafter. I do this on my .17 Hornet and 7 mm Rem Mag. Works for me.Yeah you’re right