Varmint Hunter,
I am not arguing with you here, but I posted Western's VOLUME to WEIGHT multiplier (0.7). I have also weighed several loads from 80 to 120 grains VOLUME, and my personal multiplier is 0.69.
I used two different powder measures, using both thrown charges and tapped charges scraped level. My results were different for each measure and each method and are as follows. Each measure and scale will vary slightly, so figure that into the equasion.
T/C brass measure, 100 grain VOLUME charges:
12 charges thrown, tossed out the high and low, average = 68.91 grains WEIGHT
12 charges tapped, tossed out the high and low, average = 69.88 grains WEIGHT
T/C (Flint River) U-View measure, 100 grain VOLUME charges:
12 charges thrown, tossed out the high and low, average = 68.02 grains WEIGHT
12 charges tapped, tossed out the high and low, average = 69.01 grains WEIGHT
My personal multiplier is 0.69 with my equipment, I would think that Western's measuring equipment would be way more accurate than any measures or scales we have at our disposal. I will just take there word for it and stay on the safe side of the numbers. Of course there could be other variables such as Lot # and humidity that can come into play.
If you just do the math on your numbers you will find either your measure or scale are not right.
Example: You stated 100 gr VOLUME = 73 grains WEIGHT, that would be a 0.73 multiplier. IF you used this multiplier a 120 gr VOLUME charge would WEIGH 87.6 grains, yet you mentioned your scales weighed it at 82.4, that is a 5.2 grain difference for only a 20 grain added VOLUMETRIC charge???
Now take your 120 gr VOLUME charge = 82.4 gr WEIGHT, that would be a 0.6867 multiplier. You found that to be slightly low, but maybe it was right and your 100 gr VOLUME charge above was high?
In order to check your scale against your volume measure, weigh out a 50/60/70/80/90/100/110/120 grain loads and check them against your multiplier, and I don't mean just one load of each, at least 10 loads of each to find the average and extreme spread. If your measure or scale is not calibrated, it will show up in your math, and math don't lie. I have checked mine and the numbers are very close. I had extreme spreads of 2.2 grains WEIGHT on the 100 grain VOLUME charges alone, until I tapped and settled the charges, then the extreme spread went down to 1.1 grain WEIGHT.
Just be safe guys, and know before you load!