wileybelch, it's interesting that you're using a Redding 30 caliber .328" bushing for .308 and .30-06 cases. They only make that bushing size for .30-30, 7.62mmx39 and .300-.378 Wby. Mag. cases. Redding's .308 Win. bushing sizes range from .335" to .343" and the .30-06 ones .331" -.339". Are you using that .328" bushing to neck only size cases?
I think a sizing die's .328" neck diameter for .336" loaded round neck diameter ends up with more neck tension that's needed. As there's typically a 10% to 20% spread in a bullet's release force needed to push it out of the case, the higher the average release force is, the greater the muzzle velocity spread will be.
I and many others in competition have used full length sizing dies with necks only .002" smaller than a loaded round's neck diameter for .30-06 and .308 Win. ammo in box magazine bolt guns. Rapid firing the ammo doesn't cause bullet setback from being smacked by the magazine's front wall. Single-loaded rounds for slow fire need sizing die neck diameters only .001" smaller than necks on loaded rounds.
And with a .300 Win. Mag., sizing dies with necks .003" - .004" smaller than loaded round's neck diameter on 200-gr. bullets with max loads in an 8-pound hunting rifle works well. No bullet setback on rounds in the magazine.
Redding's web site has excellent insights on neck bushing sizes; see "BUSHING SELECTION" in:
http://www.redding-reloading.com/tech-line-a-tips