Re: Help me choose a neck bushing for my Redding Die
The necks should be true when coming out of your rifle. The firing has pushed the neck brass to your chamber and almost all chambers are cut true.
IMO a bushing die should not be used with and expander ball at all. The reason you are using the bushing is to set you outside neck diameter to a specific diameter. If you then run an expander back through it you might as well be using a regular full length die.
Also the bushing dies work best with a consistant neck thickness so outside neck turning will help. If you turn your brass down to it's lowest thickness of .015" then the math would be: .308" (caliber) + .015" + .015" = .338" which should be the outside diameter of your neck after turning the brass and loading a bullet. Now it will depend upon how much bullet grip you want as to what bushing you need. A .334" bushing will give you .004" of bullet grip. That is a little stiff and I prefer .002" for ease of seating and not to cause runout.
Another thing you need to realize is that with a neck thickness variation of .015" to .018", when you size with a bushing then you will be pushing that variation to the inside of the neck. Since neck thickness variations will usually be thin on one side and thick on the other, seating a bullet with the variations on the inside will tilt the bullet and lead to lots of runout.
Turn the necks to .015" and get a .336" bushing.
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