Originally Posted by Tikkamike
I neck size only and only partially move the shoulder back when necessary because I like my shells in the chamber tight and centered. Which leads me to believe my firing pin doesnt move my case at all in the chamber.. any knowledge on this? I had never considered this theory before.
If your shell stayed fully conformed to the chamber after firing it would be almost impossible to eject. The elasticity of brass allows it to shrink (extremely small amount) so that the shell can be ejected. Neck sizing will prevent the shoulder from being set back even further, but the cartridge will still move just a miniscule amount when the firing pin hits it until it fully contacts the shoulder of your chamber and the primer ignites.
For all practical purposes your shell doesn't move much, but theoretically it is still moving just a bit until it firmly seats against the chamber and the primer is ignited.