A 1% spread in case weight's gonna produce better consistancy in load accuracy than the spread in flame and heat output across 100 primers or 100 exact charge weights of powder. Most folks knowledgable in internal ballistics feel wide spread in neck tension (release force needed on the bullet) causes a greater spread in muzzle velocity than the stuff mentioned above. Especially if you crimp (with any tool) case mouths into bullets.
Rebs, yes case with effects case capacity. Cartridge brass is uniform enough across all makes that a given cubic inch of it all weighs the same. Which means that a given case takes up so much of the volume in a chamber. Those with less weight take up less space. Their inside capacity is best determined (in my opinion) when peak pressure presses their bodies hard against the chamber wall.
Last edited by Bart B.; November 14, 2012 at 10:50 AM.