Due to the small case capacity, does it work better to weigh all powder charges or is going by volume with a good powder measure better?  I've an older plain RCBS powder measure and thrown charges can vary by as much as .3 to .4 grains ( ball powder like benchmark).
Will a better powder measure like the highly rated Redding Match Grade 3BR Powder Measure throw closer charge weights. Looking for getting the tightest groups here.

I'm a believer in volume over weight in bigger cases but with this small case I'm worried when working closer to max loads when going by volume.

Depends on the goals of your shooting. For example, target size and distance.

The powder you select has to match the goals. The weight of the bullet will affect the powder selection so decide on the bullet weight, then the most likely powders.

If those powders are ball powders like CFE or H335, then you can throw by volume and do well.

If the heavier bullets force you into a slower powder like 4895 or Varget, you can still throw by volume but shouldn't expect a tight weight spread.

With good technique on volume throws, you can throw a stick powder like Varget to within a range of about 0.5 grains or +/-0.25 grains without much effort. That represents an average velocity spread of roughly 50 fps based on just the powder spread. You have to add the other dispersion factors to that 50 fps to get your total extreme spread.

If you are not too picky about the vertical dispersion at mid range distances (say 400 to 600 yards), then there is no reason you can't get away with using your powder measure to throw.

If you are going to be shooting small targets out beyond 400 yards, you may need to weigh charges. A test will be required at the maximum distance you plan to shoot.

My targets will be 13 lined ground squirrels (aka chipmunks) so maybe 2" wide and 6" high with ranges out to 400 yds.. Vertical stringing is a big concern as I would to not have to deal with that and have to dope the wind.

I need to run some numbers through a ballistic calculator as to how much velocity spread I can cope with. I'm going to try to stay with ball powders for more consistent metering and and test loads both ways.

From Modern AdvancementsLink
I am not familiar with your powder op but if it is ball powder I would think it should  throw closer than that.
I use W748 and W760, the 748 throws majority +/- .05 gr the 760 is about twice as bad. I use Hornady measures. Most of my long range loads are thrown with my Hornady Bench Rest, though the ones on my progressive work great too.



This is what I do for speed and perfection with the above powders that throw fairly well.

I have a cheap digital scale that I have tested and tested and tested, it seems to work very well.

When loading I tare the scale, place my case tare the scale, throw the charge into the case and weigh it. If it is within +/-.04gr I keep it, if it is outside that I dump it and rethrow. I repeat this for every case, it works well and is much faster than trickling.

With 748 it is really fast because it throws better with 760 I have to dump and rethrow more often. This method is not going to work great if you get a huge variation from your powder.
This is a bit unnecessary because the loads are not really that sensitive but the time and money I have to spend to shoot long range, I want my loads the best I can make them.

One thing i have  noticed, it seems my measure likes and dislikes certain charge weight.I now take this into account when developing a load. So maybe you could try to adjust your charge a .1 or .2 either way and see if it throws more consistent.

Not sure a different measure would make much difference.

From Modern Advancements
Throw vs. Chargmaster vs. Satorius accuracy of charge.
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The OP needs to develop a rhythm to operating the UPM from RCBS.
Dryflash has posted in the reloading section some how to tips to make things work a bit better.

But, the smartest thing you can do is learn to operate it in smooth and consistent manner.
This will provide better results.  You can always throw short and trickle up to your target weight!

Use a baffle in the UPM.
Keep the hopper half full or better.

BE CONSISTENT in your operation!

So, if we can stretch ourselves just a little with respect to the work Litz shows.... indulge me for a minute...

If I can assume the Sartoruis was able to perform to it's limits, and if all the other work in terms of brass prep and loading was state of the art, then the ES (extreme spread) due to the composite of those effects including the powder charge would be roughly 60 fps. I will call this the best case scenario since it includes the better charge weight method and the baseline loading effects.

Some share of the 60 FPS is due to the powder charge spread, but if we assume it was held down to 0.05 grains then the velocity spread contribution from the charge weight in these rounds is about 10 times better than the PM methods.

If the average velocity change per weight change accounts for about 5 fps worth of that composite value, then I will conclude that you can't do much better than about 55 fps if the effect of the powder charge was zero.
Then since we have gone this far, we can assume that we would see no better than about 105 fps ES from PM rounds. If we take the SD data times six, the PM values will spread to at least 150 fps ES, and the Chargemaster will spread to at least 78 fps ES.

The SD values times six added more than these ideal values, so you can decide within those three levels shown. At the high you have the PM, better is the Charge Master, and if you have to push the limits you go with magnetic force rebalance scales and load to within one or two granules.

This is of course out of context, but later after a couple firings and a primer change for a couple loads that he knew can do better.
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Obviously it would have been difficult to tune every load to its best performance so the idea is to look at the trend not each individual data point.....and of course charge weight is only one aspect, he later gets into neck tension, flash holes, annealing, fill ratio. 



On a side note I have a problem with assuming you can go six times the SD, surely there are limits to what the extreme can be.

Some distributions are a little lopsided, but don't bet against the general six sigma concept. I have seen it flesh out too many times.

If that initial SD is based on too small a sample, you can be thrown off for a little while but not for long.

The old bosses had a habit of telling me to "go back downstairs and get off the T-Chart..." , which was their way of telling me to make sure I had a large enough sample size to know what I was risking.

They were all disciples of Deming and Juran, so they were all very versed in metrology, SPC, and DOE. I wish I had more colleagues who know their stuff these days....   I digress.

Many folks have worked with nothing fancier than the ChargeMaster and done extremely well. You can see why in the tables you shared.

I tell the younger guys that they shouldn't sweat it if they can't afford the high grade scales. The Chargemaster and wind doping skills count for more up front and they can add better scales after they can afford them.

Benchmark is not a ball powder, it is an extruded powder.

I have been playing with the newer Lee Deluxe Perfect Powder measure.  Initial tests give .1 grains of variance over 10 throws of 8208XBR which is a short grain extruded powder.  With RL15 I was getting .2 grains of variance but that has a longer grain.