It may help some but you will still see an uneven neck down if your using conventional dies, just the way it will be as there is no method of controlling the case body while the neck is sized.
Best results are had with a Redding bushing die, the competition model, not S-type. These have a sliding sleeve that has a chamber in it to match your brass. Holds the case in perfect alignment while the neck is sized so you get good even neck downs.
Easy to order one in in 260 Rem and ream it out with the 6.5 Gibbs reamer. This will solve your problem necking down cases. It will also allow you to have the perfect amount of neck tension by using different sized bushings if you want to.
Personally, if your getting some loosening of the primer pockets, your there!! Your already pushing the limits of the case and getting a measureable amount of case head expansion if your primer pockets are loosening to the degree you can feel a difference when seating a primer. I would not push it much more if it were me but that is your call.
Kirby Allen(50)