1/19/18
My records of cast bullet weights, for 26,948 bullets, shows the standard deviation average at .155 grains. A skilled caster should be able to produce 180-210 grain bullets with a standard deviation of about .125 grains; perhaps putting some outliers aside.
Then 68% of the bullets weigh +/- .125 grains, 95% weigh +/- .25 grains, and 99.45% weigh +/- .375 grains. 55 of 10,000 would weigh outside +/- .375 grains.
The questions then become:
Are groups shot with 180-210 +/- .4 grain bullets larger than groups shot with 180-210 +/- 0 grain bullets?
If so, are groups shot with 180-210 +/- .3 grain bullets larger than groups shot with 180-210 +/- 0 grain bullets?
If so, are groups shot with 180-210 +/- .3 grain bullets larger than groups shot with 180-210 +/- 0 grain bullets?
(N.B. +/- 0 is in fact,~ +/- .05 gr)
If group size differs by 10%, it seems that about 55 5-shot groups with each bullet, 110 groups or 550 bullets, are required to be reasonably confident of the difference. My guess is that this ain’t going to happen.
Instead, 5-shot groups with 4 bullets +/-0 gr and 1 bullet +/- some value, +.4 gr for example, should fairly quickly give us a notion of whether small bullet weight variations affect accuracy. This method can be used easily and inexpensively.
joe b.