Powder Measure Redux Part Five: RCBS Chargemaster
Of all steps one must perform to load for high precision shooting, powder measurement can be among the
most time consuming.
Pistol powders consist of tiny flakes that can be very accurately metered
by volume. However, Varget, which is insanely popular with the long distance shooters, is an entirely different beast.
Its sticks are big, they don't pack very consistently, and as a result most volume-based powder drop schemes fare
Enter RCBS Chargemaster. This system consists of a combination of scales and the trickler and it dispenses the powder
by trickling it into a pan on the scales. The flow is cut when the scale gets to the programmed weight.
Chargemaster has a street price of $350.
The idea behind the product is solid, and I ran a few experiments with the Chargemaster to see how precisely
it measures Varget.
As you can see, if you pour whatever it metered right into the case, the results aren't super impressive. The
standard deviation is roughly 0.11 grain, which means that the charge will almost certainly be between -0.33 and 0.33 grain
around the average, with the total span of 0.66. That's over half a grain.
However, if we throw away the drops that registered as overweight on RCBS scale, the picture improves dramatically:
The standard deviation drops about 2.5x, so the charges will now differ from the average by less than 0.15gr. Still quite
a long way from drop and trickle method, which has the dispersion half that, but much
better than unfiltered results.
The disadvantage is a very high rate of discards - to get 20 measurements that registered
at 38 on RCBS scale I had to measure 33 samples - 50% more!
A well known way to improve the accuracy of Chargemaster with Varget is to stick an inch-long segment of a McDonalds
straw inside the feed tube. The tube is threaded, and the claim is that threads cause Varget sticks to bunch up at the
end and drop in clumps. This causes the charge to go over the desired weight. McDonalds straw is just the right diameter -
it covers the threads, and eliminates the clumps.
It took me quite a while to actually get to McDonalds, but finally I made myself find one. It took me a while
to explain the salesman that I just want iced coffee - no flavors, no cream, no calories - :-) - but eventually I got
away with a cup of brown liquid and, most importantly, the straw.
Here are the results.
As you can see, the trick worked - far fewer charges went overweight (only four), and a significant improvement in standard deviation,
which was essentially halved. Unfortunately, while it made for a lot fewer discards, the accuracy of the acceptable loads
did not improve.
Overall, it is an interesting concept. In terms of accuracy, a Chargemaster with the straw mod is much more accurate than
a regular powder measure with Varget, but much less accurate than the
drop and trickle technique. In terms of speed, it takes roughly 10-15 seconds
to drop a charge with it. This is roughly equivalent to a drop and trickle, but of course much slower than a simple drop.
Given the price, the speed, and accuracy, I recommend a drop and trickle technique with a quality
balance scale and a cheap powder measure over Chargemaster.