Last Friday I measured and filled 50 tubes for the range. I need more practice to consistently get close to what you do. I began by pouring too fast with BH rolling off my hand into the bowl. When I was able to mound without leveling I was 1-3 gr. off 70 gr. by weight. I then took a single edged razor blade and slowly leveled the BH and was .2 - .4 gr off 70gr. by weight. It was tedious but interesting. The blade didn't crack and crunch the gr. like the leveler did.
I bought a Hornady electronic Lock-N'-Load (1500) scale just so I could experience the weight vs. volume comparison. As long as I kept it zeroed and checked calibration it seemed precisely accurate to .1
At times the reading toggled between two measures, like 70.1 - 70.2. I discovered that I could roll a few gr. from my fingers (wearing platex gloves ) and set the measure to 70.0 They sell a trickler to be used with this model but I saw a post where a guy cut an angled piece from a large plastic straw and kinda rolled the straw to make the gr. trickle onto the scale. It worked perfectly. In fact, if I was even 1. or more grains off 70 I could easily scoop with the straw and trickle onto the scale or scoop to remove access. Not sure if any of this is in the manual but I knew I went to the range with tubes with loads weighing precisely 70 gr. I will keep practicing your mounding technique and weighing to check my accuracy.
I recall posted comments that the scale markings on the BH 209 tubes were not precise. I gently poured 70 gr by wt into some of them and it was very close to 100 by volume. I measured some 100 by volume and put them on the scale. They were a tad off 70 gr. by weight. I tend to believe that maybe those differences in "tenths" is attributed to the density of the BH and its ability to "settle" with motion applied. I experimented - for whatever reason. I weighed 70 gr. by weight and carefully poured them into the BH tubes - in which they looked to be a good 100 gr by volume. I noticed that I could tap and flick a little on the tube and the volume reading would change as it settled. I could tap the tube on the counter a few times and consistently change the level from 100 by volume to 90. I'd just purchased a batch of Lane tubes and ended up taking those to the range. One thing I noticed is that there was no static in them. Nothing against the BH 209 tubes but I prefer the Lane tubes. Their diameter is smaller, enough that it fits into the BH tube. The narrow Lane tube was much easier for me to pour the charge into the bore with never losing a grain of powder.
Like others, I guess one day I'll decide whether to weigh by weight or volume, or both. I do recall reading that the tenths of a difference does not affect the performance of the charge. I have no idea how much difference it would take to affect the charge.