Depends on several factors.
I have seen instances where neck sizing reduced the accuracy of the given load.
The best gains in accuracy I have seen with neck sizing were with belted magnum cartridges, 7mm mag, 300 win mag, 338 win mag. I no longer neck size for my .270 or 30-06 rifle.
NRA Lifetime Member Since 1999
"I ask, sir, what is the militia? It is the whole people except for a few public officials." George Mason