Re: 7mm STW & 180 gr Bergers
Factory chambers leave alot to be desired. Especially belted mags. But belted mags are good with a good chamber fit. Thus, partial neck resize or.... as I am preparing to do soon, rechamber or rebarrel to tighter tolerances. And, I will be able to get away from the expander ball neck sizing, as I will turn necks for neck consistancy, turning them such so that the resizing die alone reduces the neck to proper size for bullet tension, improving runout.
You don't have to do half the neck. About 0.060"-0.070" or so should do for positioning in chamber. But one thing you should do, get a truly flat, as in parallel sides, washer or spacer, and when you back off your die the appropriate amount, insert spacer between die and shellholder, raise ram snug against die, and tighten die. This will help to insure alignment of case to die for resizing.
You can partial size for a few rounds, but eventually brass will grow, and be difficult to chamber, because you are not full length resizing. At which time, you would need to full length resize one time, before resuming partial sizing. Your brass will last longer using this method, than with full length resizing.
Be sure to keep the bearing surface of your bolt lugs lubed.