Powder Storage Issues

[Jim Watson]

they are all opaque to light. There's a reason for that.

Right. I leave my Dillons loaded but cover the powder measures when not in use.

A lot of the old Star Progressives had metal powder hoppers, although some had glass.
The rare Ransom Reloader had an aluminum hopper.

I once bought an old fibre can of H240. Pressures were high, so I used it up well below originally recommended loads without further ado. I thought the powder's density had been reduced by loss of solvents and moisture through the cardboard, but now wonder if it was Slamfired.

 

[Unclenick]

Tough to determine, but opacity is the common factor. The cans I have are either black or brown and have the /2\ recycling symbol and HDPE on the bottom (High-density Polyethylene).

Humidity is not particularly tough on powder, at least not at normal levels. It does affect the burn rate, though, with bone-dry rifle powder burning as much as 12% faster than powder stored in 80% RH. Norma says it stores and ships powder kept in 40-60% RH. I asked Hodgdon about it one time, and I believe they told me they used 70% RH.

Norma's print manual has graphs that show that unsealed cartridges allow enough water vapor penetration over time that if you make a cartridge in one humidity condition and store it in another, the powder will equilibrate with the new condition over a period of about one year. This is why I never store loaded ammo with a desiccant. I don't want the powder burn rate increasing by however many percentage points that particular powder can do in the low RH produced by the desiccant.

I have unintentionally shot deteriorating powder through an M1A before, and it produced fine red bore rust, despite normal cleaning having been done. That's the nitric acid at work. It came out, and boiling water and polishing with Iosso Bore Cleaner put an end to the problem.