The volume is dropped onto the scale using a Lee Perfect Powder Measure. The powder is being dropped onto a dish that is made to attach to the scale. (Tare weight is accounted for.) The scale is a Lee Safety Powder Scale. It is a balance scale, adjustable to 0.1 grains.
The powder is Alliant's Green Dot, which is a flat circular flake looking powder.
I remeasured for individual throws as requested. Since it is a smaller thing to measure, I lose some precision. But as you suggest, maybe I gain some accuracy.
When I took these new measurements I did 2 things different:
1- I rechecked the 0 balance on the scale. I think this needed slight adjusting, so I adjusted it.
2- I filled the powder measure hopper to near the top per a-driver's comment. In the previous data, it was half full.
Here are the new results in grains:
5.9
5.7
5.7
6.0
5.9
5.8
5.9
6.0
5.7
5.9
min 5.7
max 6.0
avg 5.9
median 5.9
sample std dev 0.12
Obviously, I'll need to back off on the volume setting to recenter on 5.8grains. If this is typical and accepted variation per throw, then I might center a little lower to keep the distribution tails below 5.9.
You haven't told us what powder, but it doesn't really matter in the context of your question. But you also haven't told us how you are measuring your powder. IMHO you are concerned about the wrong things. The powder DENSITY doesn't matter at all. All that matters is that you get the correct charge of powder in each case.
That answers my first question, thanks. I'll ignore the density calculations and any difference between my measurements and the published estimates.
That just leaves the other question, is the variability per throw that I am measuring reasonable/typical and acceptable?