This issue comes up often. The issue is probably not so much the measure as it is the technique employed in using the measure. Here is a "tips" article I wrote some time back....
• First and foremost should be a sturdy Powder Measure (PM) stand that holds your PM about 2 inches above the table and extends the outlet about 3 inches away from the post. You can buy these stands from RCBS and Lyman, or you can build one from wood scraps in your shop. You'll want the base to be plenty heavy so that it won't jump around, and the stand to be solid so that the PM doesn't wave around like a flag on a pole.
• Accurate measurement of powder depends on several things; one of the most important is consistent powder
density. So when measuring powder I use a technique called "knock-knock". Whenever the micrometer adjuster reaches either end of the stroke I simply hit the stop twice. All this vibration gets the powder to sift down to a constant density so that with each throw, the contents of the PM chamber are more consistent. And therefore the weights are more consistent. So when you operate the PM, you raise the handle and hit the stop twice (knock-knock), and then you lower the handle to dump and hit the stop twice (knock-knock). This may take some practice on your part.
• Never use the first 10 "dumps" from the PM. Simply put them back into the top of the hopper. The first dumps out of the PM simply haven't shaken down enough to become a consistent density. On a volumetric PM, it's impossible to get consistent weights of powder without consistent
density.
• These PMs are also helped by a "baffle". Explanation and design attached. We're talking 5 minutes with scissors and a beer can.
Click Here for instructions on how to make your own. The most enjoyable part is emptying the can.
• You can best “dial-in” your powder measure adjustment by averaging. Say you want 11.4 grains per load. Try adjusting your powder measure until 10 loads weigh a total of 114.0 grains. You'll get much closer to a perfect 11.4gr by using this method than you will weighing single loads.
• If you ever need to lube your measure, use only powdered graphite. If you use your PM often enough, the graphite on the gunpowder (the gray coating is graphite) will self-lube the measure for you.
• Another tip is to get (or make) a "reloading tray" (
http://www.midwayusa.com/viewProduct/?productNumber=576361 ). As you prime your cases, put them mouth-up into the tray. When you have a goodly number, say 40-50, then dump powder into all of them in a single session. That way you get very good at knock-knock. AND you can take a bright light and inspect all the cases for equal powder height.
• Some powder measures, such as the RCBS Uniflow, have separate large and small rotors. You must match the large rotor to rifle loads and the small rotor to pistol loads.
• Finally, don't ever leave powder in the hopper. Always put it back in the can. The acid in the powder will etch the plastic cylinder pretty badly. The gray color is a natural consequence of using gun powder. Nothing you can do about that except to convert to a glass hopper.
It also helps to remember that NO powder measure is absolutely perfect. Better powder measures get better at delivering consistent "dumps", but they will all wander by some tiny amount.
Hope this helps!
