When I used to handload my ammo, I neck sized only for my Ruger 77 (308Win.), and never had a problem.
Its that one time you do that counts. There has been trouble necksizing only by several shooters.
Mossy, i believe it has to do with the give of the case acually fireforming. That give is enough to slow it down some. Thats why I see spreads go way down with necksizing. With a fireformed case, there should be a slight pressure spike due to no give. It should go down quickly