Slight apologies -- I don't see much bad advise on this thread -- save for Al's uncharacteristic "too quick" read -- It does happen, though, from both knowledgeable people like me (& Al) when we misunderstand, and from others, who, as I said, just repeat what some guy told them.
That out of the way, & why I seem to keep coming back to this thread, something just doesn't quite add up with the numbers. I'd add my encouragement to Mike & Michael to get a knowledgeable smith or shooter to take a look. I think some of your reported measurements might be wrong. Might not, too, but something just doesn't feel right.
BTW, for brass springback, here is a link to Varmint Al, well worth reading:
http://www.varmintal.com/arelo.htm
(Here's the significant part to neck tension. Remember, he's using conventional dies, oversizing then expanding up with a mandrel or button...
ANNEALING AND NECK TENSION.... Uniform neck tension is another reason to anneal your case necks. Each time you neck size and then the expander ball opens the neck up to the correct diameter, the brass' yield strength increases. It is called strain hardening. As the yield stress increases, there is more spring-back (to a smaller neck ID) after the expander ball opens up the neck. This effect increases the neck tension. A new annealed neck will have less neck tension than a case that has been fired and neck sized a number of times. Cartridge brass is 70% copper and 30% zinc and its yield stress and strength is increased by cold working.
Annealed cartridge brass has a yield stress of 19,000 psi.
¼ hard cartridge brass has a yield stress of 40,000 psi.
½ hard cartridge brass has a yield stress of 52,000 psi.
So the neck tension on a ¼ hard neck will be twice that of a freshly annealed neck. If your rifle's chamber neck clearance is large, then you could easily get to the ¼ hard condition in 5 or 6 reloading cycles. It would take more cycles if your chamber neck is close fitting.
* * *
The funnel shape of necks that Al Nyhus remarks on seems to be a constant phenomena. I get it with necking down as well as necking up. One of my wildcats is an 8x68-S necked down to .30, with a longer neck. I believe that because the brass of the shoulder in some manner "supports" the brass in the neck it is closer to, I get the funnel shape.
Went so far as to set up my case forming workflow to include a step to inside ream the necks before final outside turning. I do get dead-straight necks, and even wall thickness but don't believe I can really shoot the difference. Maybe when it's dead calm...
It's just one of those things you have to go through & decide for yourself whether or not it's worth the effort.
One thing I *think* no one's mentioned -- Wilson bushings are tapered, and many dies only size a portion of the neck. the .30 BR has a long enough neck that if you're seating bullets so the pressure ring is quite deep, you may not be getting the sizing at the pressure ring that the number on the bushing reads.
But do take your cases, bullets, dies (esp. bushings) & esp, measuring tools to a smith or very knowledgeable shooter. As several have said, something just doesn't feel right.
