Bigmon,
Your post prompted me to take a very quick look at three different Hornady swaged roundballs marked on the boxs as 490, .570 and .310.
Measuring 5 different balls they varied as follows:
.497 to .491
,570 to .573
.303 to .312
As you suggested, you can get about any number you want on a given ball based how you turned it and care in placing the mike.
Weights were as follows:
Nominal .50 balls: 178.3, 178.8, 178.7, 178.3, and 179.1 grains
Nominal .570 balls: 279.1, 279.9, 279.4, 280.0, and 279.4 grains
Nominal .310 balls: 44.9, 44.9, 44.9, 44.9, and 45.0 grains
I think that I now need to go back and see what my cast round balls run. I expect that, in addition to my technique, different molds and manufacturers of the mold would introduce measurable variation in roundness and weights thrown. Then, of course, there is the influence of lead purity on cast weight. I'm sure that someone on the forum has done a more critical evaluation that my "quickie".
I am also sure that the above variation pales when compared to the variation produced by my aging eyes, etc. on my shooting!
J.B.