Via email from Roger W. we have this from Hodgdon:
Powder Storage in Reloader Hoppers
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.
Roger sent them an email questioned them on this (“Why not leave powder in powder measure hoppers for extended periods?”) and got the following reply:
There are a couple reasons.
Despite warning some people have multiple powders on their bench, they leave the powder in the hopper for long period of times and they forget or think they know which powder is in the hopper, they pour it back into the wrong canister and there will be a problem. this may seem like common sense but we see this happen every week from a phone call or an email.
Some powders that are made today have a very high Nitroglycerin content to them, when left in powder measures for a period of time the Nitro will seem to eat the plastic. We have seen this with standard hand thrown powder measures and electronic ones that will get ruined.
Powder has a built in moisture content to it. the proper storage of powder is in the canister with the lid shut tight, this will help keep the moisture in the powder. Most likely there would not be a problem with moisture left in a hopper unless the lid is accidently not put back on.
Mike Van Dyke
Customer Service Representative
Hodgdon Powder Company
6430 Vista Drive
Shawnee, Ks. 66218
913-362-9455 Ext. 109
I have plastic powder measures that are yellowed and I attributed it to an interaction with the powder. But I have never seen any that appear to have been eaten. Still, I probably should be more careful about leaving the powder in the measure for extended periods of time.