LineStretcher, that is an interesting question that had not occurred to me to ask. Temperature stabilization is achieved by playing with deterrent coatings on stick powders. Since the powder under the coating is the same basic stuff, I don’t see why that would change its ability to pick up moisture. It might change how long it takes to equalize, but if you are thinking it would better waterproof the powder, keep in mind that water vapor transmission rates have measurable lower limits for most anything but glass and metals, so it gets through even plastic powder jars eventually.
I saw that dispensing system or one very like it at the Indiana NRA Annual Meeting's gun show. It was paired with a scale that uses an electromagnetic load cell rather than the usual strain gauge type. That makes it less prone to drift. It is a cool machine.
The only issue I have with relying on weight alone is packing density remains a variable. Back in the 1920's Hatcher described selecting a powder for that year's National Match load. He had two candidates. Both had burn rates similar to modern IMR4320. One was a short grain that the Frankford Arsenal (it was still an actual government arsenal back then) loading equipment's powder measures could throw to an accuracy spanning 0.6 grains (±0.3 grains). The other was a long stick similar to modern IMR4064 that the arsenal loading equipment's powder measure could only hold to a span of 1.7 grains (±0.85 grains). Yet, in test after test, loads produced with the latter dispensed powder were more accurate and that powder was selected for that year's NM ammo. A competitor who had brought tools and a scale pulled some of the ammo down and announced to everyone that it had to be bad ammo because of the wild charge weight variation. Several records were set with it that year.
It turns out that with stick powders in general, packing density affects burn rate. If it packs tighter into the powder measure's metering cavity and falls tighter into the case, it acts like a heavier charge of slower powder. If, as Hatcher did, you get lucky, the effect cancels out the increase in charge weight.
In many instances, though, the effects of packing and charge weight variation do not cancel out and you just have another source of performance variation. This phenomenon was observed by the late Dan Hackett, who was a benchrest competitor. He described a load that worked great when assembled at his home bench but that produced sticky bolt lift (too much pressure) when loaded at the range. He finally worked out that the vibration resulting from transporting it to the range was settling the powder just enough to lower its burn rate enough to be a good load. When assembled at the range without that settling, it produced significantly higher pressure.
So, what's a fellow to do. My current working method for test loads involves eliminating as many variables as possible so I can achieve the load’s potential during testing. For the powder, I tare a scale with the primed case, dispense stick powder into it with a JDS Quick Measure, which is seldom off target by more than a tenth of a grain in the first place, and then put it back on the scale and trickle up to the last tenth. It’s slow going, but not as slow as setting the scale for final value and just rejecting and dumping every throw that isn’t right on the target weight. I’d started with that, but I realized from looking at recovered open-base bullets that have the shape of the grains impressed into their exposed lead, the top few grains will be packed hard against the bullet by pressure and be the last to burn, so they won’t contribute significantly to net flame front propagation rate, so I felt it was OK to drop the more rigid practice and haven’t noticed any difference afterward.
So, I would, ideally, hope for a version of that dispenser that dropped powder straight into a charged case. Absent that, using a funnel and drop tube and dropping from a weighing pan into it in a consistent fashion is what I would do to get the most out of it. My objective in testing is to find a flat spot that isn’t sensitive to exact charge and then I can set my measure and forget the extra time needed for careful weight dispensing. But to accurately define those limits, I still need a good scale and consistent RH.
