thanks for the math, Denton! that's just what i was trying to ask.
I have no doubt that 20 FPS is better than most, but for long range precision, much lower is required.
I try to keep SD in the low single digits. sometimes it creeps up to 10-12 fps. but an SD of 20 fps would be right out!
I do weigh to the kernel of powder and I do use varget in 6.5x47L and 6dasher. IME a kernel is about .01-.02 grains, but it's hard to tell since my acculab scale only resolves to .02 grains (i.e. it goes from .00 to .02 to .04, etc)
so the real question is, can i skip a time consuming weighing process by simply throwing 4 times. if my +/- .2 dropped to +/- .1 grain (the factor of 2), and in my dasher, for instance, .1g is about 9fps, which would be 18 fps at +/- .1g. so if i start with say, an SD of 6 fps, and add 18 to it, trying to use your math, I get an SD of 19, but I don't think that's right at all.
here's an example of two (not particularly good) 6dasher loads shot round robin with 31 and 31.2g varget. i've used excel to calc the mean, ES and SD for both groups individually. and if I also pretend it was one 31.10g group with +/- .10 grain variation, it gives me an ES of 36 and SD of 11. (though obviously, that's not how it would work as shots would be clustered more in the middle. i think that's more of a worst case)
Using those numbers, the SD of 11 gives me a .2 mil vertical at 1000 yards, which is 7.2" while the SD of 6 is a .1 mil vertical or 3.6" (for reference, F-class x-ring is 5" diameter) so I don't think I'd even want to use that to practice. Basically, I'd have to throw 16x 1.9g charges instead of dropping 4 times.
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