PROPER POWDER STORAGE
Some years ago I read an article by Charles “Skeeter” Skelton, the handgun editor of Shooting Times magazine. He told a story of how he had loaded up what he called “stout” loads for a friend. The friend tried to shoot a range bull that was down and needed to be killed. The rounds went “poop” and bounced off the bull’s skull at point blank range. Skeeter went back and checked his powder measure which had been left with the powder in it for quite some time prior to cooking up the loads. When he dumped the powder out he found lots of it adhering, actually melted into the plastic hopper. He realized that the chemical reaction between the powder and the plastic hopper caused degradation of the powder. He was correct as this is the first reasons you should empty the powder back into the bottle after a reloading session.
When I first started reloading, I recall reading from loading manuals of the day that there were a number possible problems from leaving powder in the hopper.
1. Powder attacking the plastic hopper and degrading the powder as in the previous story. Nitrocellulose powders are extruded thru use of a solvent, Acetone mainly, to soften it and make it plastic for processing it. Acetone can melt or soften polystyrene plastics. Nitroglycerine-augmented nitrocellulose powders (double-base) involve even more solvents to introduce the EXTRA nitro into the guncotton.
2. Confusion later as to which powder is in the hopper leading to using the wrong amount/weight of powder in a load.
3. Powder being adversely affected by UV light (from a window or fluorescent lights), leading to decomposition or change in burning rate. Powder comes in opaque cans for a reason, powder will degrade in light over time.
4. Degradation of the powder from exposure to humidity because a hopper will not seal as well as the powder bottle or jug. Smokeless powder is hydrophilic (it will absorb humidity from the air) and when it absorbs water, it swells and this will change the burning characteristics of the powder. Only the top half inch or so will swell like this. This makes any later charges thrown from that powder less powerful than the first charges thrown from dry powder, but not consistently so. Most basement reloading rooms have higher humidity than any other room in the house (excepting the bathroom). The manufacturers go to great pains to maintain consistent moisture levels for every batch they make. For that reason alone you should store your powder in a tightly sealed original can after each loading session.
I highly recommend using the proper powder storage procedures and as a final point of emphasis is the following statement found on the Hodgdon’s reloading data website: “Powder left in the reloader’s powder measure hoppers for extended periods, overnight or several days, should be avoided. Powder needs to be stored in original containers ONLY, when not in use. Numerous modern smokeless powders are double base in construction, containing both Nitrocellulose and Nitroglycerine.”