There is another aspect to powder charging that is often never mentioned.
This may or may not relate to your issue, but if a load is even mildly/slightly compressed HOW that charge is poured into the case CAN have a dramatic affect on HOW that powder burns from shot to shot.
An example, I used to throw my powder directly into each case from the measure then when all done I would seat bullets. With compressed loads I noticed the resistance to seating varied, as did the amount of crunching powder.
Anyway, I had just tested a batch for the following weekends F-Class match, and loaded them up. ES/SD were very low and the load was good to go.
It was 4+ hour drive away for the comp, as soon as I got there and set up I wanted to shoot a few sighters outside of the comp area, the very first shot was excessively loud and the bolt was locked solidly shut. I was perplexed, to say the least.
Now I loaded and shot those cases straight from the loading bench to my shooting table and had 10 shots that were fine. The brass had 10 loads on them and was sorted by H20 and was stable.
My conclusion was that something had changed on the drive to the comp. When I got home after a failed trip and a ruined extractor, I pulled the bullets and noticed that the powder was now a fair way down in the case, so I took an empty case and charged it as normal and compared them, it was a significant difference in powder height.
After some experimenting, I discovered that if I threw my charges into the scale pan, then holding it to the side of a funnel and allowing the powder to swirl and not bunch at the bottom, it needs to be a constant swirl like a tornado, no bunching or starting and stopping for best results. I could achieve the same affect in my powder packing scheme. Bullets are easier to seat and the powder crunching is hardly there.
Once I had adjusted the charge weight, that same load/powder combo shot even tighter but only raised pressure with that particular powder/bullet combo.
I now load all of my charges that way and it HAS definitely made a difference to my ES/SD for the better nearly every time in tuning a load.
So, I discovered inconsistent powder column height had a detrimental affect to how the powder burns between shots.
Cheers.