I haven't posted much but I've run into the same conundrum. What started off nice, went south. Barrel leaded up even shooting loads that produced good groups initially with boolits cast at the same time and no other change in components. Tried powder coat vs traditional lube but no improvement. Sat down with my targets and notes 2 weeks ago trying to figure out where things went bad, the only constant was a 100 - 150fps increase in MV, so I reduced charge weight to velocities that previously shot well without much improvement.
During last Saturday's match my best 5 shot group was 1.52" with an agg of 1.87", best 10 shot group was 2.4" with an agg of 3.32". Score was a dismal 162. Chono'd velocity with 25.4gr N135 averaged 2167fps with SD of 5.0 and ES of 16.
Recalled I was plagued by similar problems with my 6.5CM until I slowed it down so pulled the tech data from the 2021 CBA Nationals and found 10 competitors shot 30BR. Here's what I found:
9 of 10 used linotype
8 used Fed 205M, 1 used Win SR and 1 used Win SP
Avg barrel length - 24"
Avg twist - 12
Avg velocity - 1960fps
Avg boolit weight - 194.7gr
All competitors used lube and gas checks
3 used Varget, 2 used A2495, 2 used N135, 1ea used N133, IMR3031, IMR8208
The grand national champion shot a 30BR with a 12T 24" Shilen using 207gr boolit over 29gr A2495, Fed 205M, at a chrono'd velocity of 1750fps.
I've re-run QL with the Ba factor adjusted to match actual chrono data at two low nodes with predicted velocties of 1821 & 1909fps. Had hoped to shoot this morning but is raining, maybe tomorrow if weather clears up.
RPM of my current load is over 173k, the new loads will drop rpm to 145k & 152k respectively and fully expect one or both to shoot well. Found a great deal on pure linotype direct from a printer for $1.45/lb delivered and have 110lbs enroute.
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