Just started neck size only on 7mm RUM, FL size with RCBS had case separations starting with third reload. Min. side load of 84 grains of RL-25 with Hornady 154 GR. SST and Fed 215 primer, getting 3100 fps. This is in a Savage 116 that has had the headspace checked. I'm starting to wonder about the finish in the chamber effecting case stretch, even with neck size only, I see just the slightest flattening of the primer into the primer pocket radius. Bullet is not touching the rifling by a long way 1/8" or better as they are loaded to fit magazine. Remington Factory ammo (160 gr. Nosler), shows more pronounced "hat" on fired primer and 3220 fps. First firing of unprimed Rem brass doesn't seem to fire form shoulder as far forward as factory round by .002. as measured with RCBS Precision case mic.?? Just started neck size only, and interested to see how cases perform after two-three firings.