Finally found my old plot sheet I used when testing my new Kreiger barrel in my .30-.338 Keele Mag. (.300 Win. Mag. cases full length sized in a standard .30-.338 Win. Mag die; neck's a bit longer). All 30 shots fired consecutive, once every 20 to 30 seconds.
Sierra 190's (black dots) were previously fired, then full length sized normally then again with a body die to get the ridge next to the belt reduced to new case diameter. Die's neck was lapped out to 2 thousandths smaller than loaded round neck diameter.
Sierra 200's (red dots) were fired in new, virgin brass, just full length sized to set the .300 Win Mag shoulder back, no neck turning or any case prep at all.
Chamber's a standard SAAMI dimension.
Here's what my .308 Palma rifle does with full length sized cases:
I tried neck sizing, partial neck sizing with both barrels when new. Groups were 2 to 4 times as big; largest with partial neck sizing with the bolt binding ever so slightly when closed on a round.