Regarding brass capacity, a poster stated that brass should be sorted by weight, so as to keep case capacity consistent. That does not work. The weight of a case has no statistically significant relationship to that case's water capacity. I did a test: First, I took 60 Lapua cases and 60 random-year Lake City Match cases. I weighed them and checked the water capacity. The bell curve on both was identical (not the same capacity, but the shape of the curve, and the extreme range was the same). Then I took 9 cases that were all right in the middle of the bell curve, and loaded them; also 9 cases, 5 from one end of the curve, and 4 from the far end of the curve. There was a difference in those cases of 0.6 or 0.7 gr capacity. Same load in both sets of cases. Same shooter, same rifle, same conditions (indoors at 100 yards). The 9-shot group of cases which all had the exact same capacity shot 0.712". The 9 cases from the extreme ends of the weight curve shot 0.706". Those were the Lake City cases.
I have not seen better results from Lapua than from Lake City, and have one 4-shot group from the Lake City batch (random years of LC Match, not sorted in any way) that is 0.022". Hornady 6.5 Creedmoor cases have a significantly larger variation in capacity, but they also shoot very well. One group of unsorted Hornady 6.5 CM cases gave a 5-shot group of 0.165" (first four shots in 0.01x"), and this was backed up by a 5-shot group measuring 0.250". Rifle was a Savage 10 FCP/McMillan, bedded with Acraglas gel, no pillars, and a diamond-lapped factory 26" chrome moly takeoff barrel set back and rechambered with the PT&G 0.199 freebore reamer. That was a test of neck turning. The turned necks gave the larger group. Again, BR shooters don't turn necks to improve accuracy, but to be confident of consistency, and to make the cases fit in custom tight-necked chambers, with a known clearance that is very small, without bullet interference on firing. On David Tubb's extreme long-range record he used necks with about 5 thousandths clearance total on both sides (2+ thou per side), but cartridge body clearance of 2 thou or slightly less (< or right at 1 thou per side). You'll have to do your own testing, but that's what I did, and that's what I've heard David Tubb say he did, to get those results.