(...) I have a very recent example to provide as a reason for sorting when precision matters.
.30 WCF
150 gr Speer HCRN (discontinued )
2.545" COAL
2.228" case length
32.5 gr IMR4895
WLR primer, lot *638G
Tested in "tight"-chambered 16.25" barrel. (Loose by match standards, very tight by production .30-30 standards.)
Load initially developed in FC brass (single lot).
Load later tested in other brands of brass.
Benchmark velocity (FC brass): 2118 fps
R-P brass: 2066 fps
Win brass: 2161 fps
W-W brass: 2144 fps
R-P brass, lot 2: 2226 fps
All extreme spreads were under 50 fps - most under 30 fps.
Standard deviation peaked at 19.98 fps for the R-P brass (lot 2). All others were 13 fps or less.
If you didn't catch it, the two different lots of R-P brass were 160 fps apart (7.7%).
I have not weighed, nor checked H2O capacity of either lot; but I can tell you that lot #2 was from the '60s or '70s and the other lot was from about 2010. Externally, though, they look exactly the same.
Same components.
Same conditions.
Loaded at the same time.
Fired at the same time.
Dramatically different result.
Mix one of those 2226 fps bad boys in with the already-slower 2066 fps lot, and you'll have a flyer. In this case, it isn't just the trajectory that matters, either. When this load hits 2,200+ fps, the groups scatter - ragardless of brand of brass.
For these particular loads in R-P brass, fired from that rifle, the velocity difference results in a 2.25" higher point of impact at 200 yards. And the difference is 6.1" at 300 yards. Significant.