Re: New Brass Company in town...
Here's some stuff based on observations I've seen over the years...
Neck and body wall thickness uniformity is in second place for new cases to shoot the best. They can have a .001- to .002-inch spread and shoot great IF the shoulder, belt and head are square with the case long axis. Besides, many folks turn case necks to the thickness they want for their chamber necks.
Most important is having the case head square. With square case heads, wall thickness spread can be .002-inch for the body, .001-inch for the neck and new cases will shoot virtually as accurate as 99.9% of any resized ones; especially with belted cases. Otherwise, you have to shoot them with maximum loads once or twice in rifles with bolt faces squared with the chamber axis to square them up. Of couse with non-square bolt faces, they'll only shoot most accurate when first fired; reloading them won't help and they'll then shoot less accurate than when new. Same thing for belted case belts and rimless or rebated rim case shoulders; they all have to be square with the case axis. When driven hard forward by the firing pin, they'll make even contact all the way around where they stop against the chamber.
Rimless or rebated rim cases should have headspace between .003- and .002-inch shorter than the GO chamber headspace gage for the cartridge. Belted cases should headspace .001- to .002-inch less than the GO chamber headspace gage for them. New belted case shoulders should have about .003-inches clearance to the chamber shoulder when that chamber has its belt headspace at maximum and its shoulder at the SAAMI minimum.
Case weight should have no more than a 1% spread. If not, one can easily sort them by weight into 1-grain spread groups. This is less important than heads, belts and shoulders being square.
The smoother the primer pockets' surface can be, the easier the primer and powder residue will clean out. And drill those flash holes unless they can be punched very cleanly.
Best wishes in your endeavour.