I did my first serious examination of my newly modified RCBS and Hornady dies, both of which have been converted to use Redding neck bushings by JLC Precision.  I had a small problem with the Whidden resizing die and had to send it back for an adjustment.

I took some fired brass and ran measurements:
a. Length at shoulder using a .375" collet - 1.784"
b. Neck dia. - .340"
c. Shoulder dia. - .422"
d. Gas ring dia. - .456"

Measurements after resizing with the RCBS and Hornady bushing dies (both measured the same):
a. Length at shoulder using a .375" collet - 1.780"
b. Neck dia. - .3335"
c. Shoulder dia. - .420"
d. Gas ring dia. - .454" 

Runout of the cases after resizing ranged from .000" - .002".

Runout of the loaded rounds (using the Whidden micrometer seating die) ranged from .000" - .005". 

I only fired 10 test rounds using my 220 grain Hornady RN load (40 grains of IMR4350 with a CCI Large Rifle Magnum primer finished off with a Lee Factory Crimp die); however, I saw a definite improvement in accuracy.

The JLC modified sizing dies were well worth the money.