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Neck sizing dies are not designed to change any part of the case except the neck's diameter. They are not designed to push the shoulder back at all.

After firing, the case will expand and swell and depending on op rod/bolt dwell time (how long it takes for the bolt to start to open) and a few other things your cases can expend in length enough to exceed the SAAMI headspace specification. This is why, at a minimum, full length resizing dies are recommended. Some rifles, with tight chambers, require a small base die but that is the exception.

Full length and small base dies can be adjusted to push the shoulder back (bump) a few thousandths of an inch. The small base die also reduces the diameter of the base of the case.

As an aside, are you greasing your cases or just leaving them greasy from the resizing step. Some people recommend applying a thin coat of grease or oil to the case before firing; I don't and neither does Springfield or the military. While the lubricant can increase case life, by allowing the case to move toward the bolt face upon firing and thereby reducing the stretch at the base of the case, that puts more pressure on the bolt lugs and it forces more stretch on the other end of the case...the shoulder area.
 

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RAMMAC,

Forster Neck Bushing Dies will push the shoulder back. I use mine (without the bushing insert) to push back the shoulder on full length sized cases that still don't have enough headspace clearance.

JD
That's because the Forster "Bushing Bump Neck Sizing Die" isn't a true neck sizing die. They use the word "Bump" in the name of the die because it is designed to move the shoulder in addition to the neck sizing capability.

http://www.forsterproducts.com/store.asp?pid=27654

This die is a combination of the Redding S type die that uses bushings to adjust the neck diameter and a standard full length die.
 
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