Comments from someone that did a lot of statistical process control and also weight counting as a manufacturing engineer in an earlier life. This is my overall summary since getting back into reloading and having the time, now retired, to do some tests and also have reloaded over 2500 rounds in the past year or so.
I use the RCBS uniflow. Have the typical Balance scale. Think it is Redding and was bought circa 1968.
First, I mounted the Redding scale on a separate shelf around eye level. I used a small strip of aluminum strapping and screws to hold it in place on the shelf. I put two thicknesses of duct tape under the leveling screw. With it held in place, the zero stays constant and the tape absorbs vibrations and being on an isolated shelf keep it accurate.
Next up was to experiment with my powder flow or charging techniques. BTW, I did discuss this with a buddy that did some match shooting over the years and he, independently, has been working on the same charging techniques and we both came up with the same conclusions....we are delivering MORE consistent charges.
Here are our basics....
Fill the reservoir close to the top. The more weight or mass in the reservoir, the more consistent.
Tap, using your fingers...not a hammer...the side of the reservoir about 10 times randomly around the circumference to settle or distribute the powder.
When you hold the reloading tray, or an individual shell, under the dispensing tube, LIGHTLY hold it in place. Do not force or push upward.
The charging technique it to consistently raise the lever and let it just barely touch the stop or the top. Don’t slam it up or go crazy. That gives you a more consistent fill. Then the same thing on the downstroke.
We each USED to snap the handle smartly against the top stroke...thinking that the vibration or impact would keep the powder uniform. NOPE. Just the opposite. More inconsistency.
When the level in the reservoir drops more than an inch....replenish it. I found that when it dropped around 1/2 - 3/4 inch, my results were a little better if I tapped the sides to resettle the powder. Obviously retap the sides when you add more powder. I DID disassemble the powder measure to make sure there was not any residue or build up. Cleaned all the surfaces with a soft rag (cotton T shirt).
The ONLY other comment is on the powder. Several Bullseye shooters and other competitors recommended the N-310 for 45 and the N-330 for 9mm. CFE Pistol was also recommend for both. I have loaded a variety of rifle and pistol calibers over the years. After changing my techniques and using either of these two powders, I am convinced that I have the best loads possible. For casual plinking we both chose Unique. The above tightened up our charges....so they should improve your charging accuracy regardless of powder.
NOW, if you get into competition and measure the shell capacities and throw out the highs and lows; sort bullets for weight and concentricity, digitally weigh every charge, etc......you WILL have better ammo. But for us and many competition shooters, these are the best methods.
BTW... we both weigh about every 8th to 12th charge and if you don’t keep the reservoir level consistent (within the original level....at say down an inch), your charges will lighten up. Maybe 0.1 - 0.2 gr. That might be spread over a 50 round tray....so the charges WILL lighten up as the level drops.
The ONLY other change was in our “processing”. We have started to run 200 - 300 shells through the sizing, depriming, belling and priming stages (first two dies). We store the shells (usually sorted by headstamps) in plastic jars or bags. Then when we need ammo, we just charge and seat. That allows us to focus on the accuracy.
I also found that many competitive shooters do the same.
This is our experimental results and conclusions.....others may have different opinion and results.