No, neck sizing is not totally necessary or even advisable for some hunting situations, butbecause now I don'twant to spend as much timedoing this (reloading)as I used to, that's usually all I do to my brass any more. The Lee collet neck die makesthis simple because there's no case lube involved and very little to adjust. You might need to polish the mandrel as bc said to get a little better neck tension, but that's a one time operation. Then again you can buy an undersized mandrel directly from Lee. Another couple of things I like about the collet die is that it generally makes very straight ammo, which helps with accuracy, and it works the brass a minimum amount, which makes it last longer.