Tuning the 212 gn Seneca load for the 300 WSM:
OK, so i gave up on 4000 MR as it was too temp sensitive, and tried H4831 long grain, H4831SC short grain, and IMR 4350:
H4831 long grain worked, but required a fairly compressed load, not really enough case capacity in the 300 WSM case, and got to 2960 fps without major pressure problems, but did produce “clickers” at the top end (ADG brass). But want to keep my limited supplies of this powder for the 225 ELDM in the 30” 8 twist barrel.
H4831SC (short grain) ran into pressure at 2923 fps, also a compressed load, and had a 1.0 wide flat spot at almost exactly the same speed as IMR4350 and H4831 long grain. Probably not a coincidence.
Next tried IMR 4350, which worked well enough to get me to 2935 fps from a 7 twist 28” MPA barrel, without pressure, and with casecapacity to spare. SD was a respectable 5.5 fps on a hot Texas summer’s day that started at 84 and ended at 95 deg F. [Even though IMR 4350 is not officially a temp stabilized powder, it does quite well in this regard, in my experience.] But clickers appeared at 2955 fps so took 2940 fps as the max.
Found a flat spot between 2930 and 2940 fps that was 1.0 grain wide. So loaded to the bottom end of that flat spot (2930), and tested seating depth from 20 thou to 60 thou in steps of 3 thou, using up way too many components! Found two candidates that produced groups below 0.5”, one at a 45 thou jump, and the second at 55 thou. The very short jumps (20-35 thou) all gave 2 shot “groups” between 0.9 and 2.3”, kinda ugly. Also, it looks like very narrow seating depth ranges where the bullet/powder combo groups well. Not sure that would make for a reliable load. [Might need to try 5-20 thou range some day when i have new bullets in hand.]
But surprisingly, i found that very long jump (135 thou and 145 thou) both gave 0.3” groups, with bullet holes touching. Same group size as 4000MR. This looks more promising, will see if it repeats. I am hopeful.
Disclaimer: It is difficult to determine exactly where the bullet’s front pressure/alignment ring (not at full diameter yet) touched the lands, easy to push that through into the lands, so my jump numbers might be way off. [COAL is perhaps more reliable than boat-tail-to-ogive for this bullet.]