Re: Brass sizing.................
I'm sure the gunsmith meant 'full length' sizing.
If the cartridge is highly improved, the chamber is fully fitted, and load pressures are moderate, then it actually is possible to reload with only shoulder bumping.
If the shoulder angles are high enough(45-60deg),, occasional bumping.
Little of this is common though.
Springback only, does not work harden brass. It takes a bit of actual sizing both directions to do this. And work hardened brass does not spring back less.
Annealed brass springs back less.
Yielding brass springs back to different dimensions.
Hardened brass and/or thicker brass, springs back more.
With this, the only way to recover over annealed necks is to cycle size them until springback(your tension) returns.