Very Interesting, Fuj.
You groups are really good and show a distinct preference for 2,882 to 2,895 fps but the differences in the change in velocity for the same increase in powder charge confused me.
Normally, I find that adding 0.1 grain of powder charge results in from 5.5 to 6 fps increase and it is usually surprisingly linear for a pretty wide range of powders across a pretty wide range of velocities.
I've tested about 30 different powders and they were all about the same for both the slow burning powders and the fast burning powders.
It might be possible for temperature sensitive powders to gain velocity if there were a very large temperature change (maybe a round sitting in a hot barrel for a while before it was fired) but a 2.3x difference in velocity change is a big larger than I would have expected, since even the most sensitive powders increase only about 1.24 fps per deg F.
Your photo shows a 13 fps difference between 1st and 2nd group and 31 fps between 2nd and 3rd group with a total of 44 fps between the 1st and 3rd. That works out to be 7.33 fps per 0.1 grain of powder difference overall, which is greater than I expected, but wouldn't be all that different than what I would have expected if you were using a powder that I have never tested or you experienced a significant rise in temperature between the second group and the third group.
But the first two were 4.33 fps per 0.1 grain and the next two were 10.33 per 0.1 grain. That is a pretty big difference for the same delta powder increase.
Any idea why the differences for the same change in powder load weren't more linear?
Or do I need to retest some of my powders?
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Originally Posted by CFJunkie
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