Some time ago I had noticed a peculiar smell when I opened the powder safe. I also found an unusual buildup of what looks like rust on the inside of the door.
Putting together some loads the last of the IMR 4166, I noticed the fine residue. It's finer than talc.
No idea what it is, but something like that can definitely accelerate the formation of rust if it absorbs moisture.
I checked the other IMR powders I have left, they don't have that problem.
The color of the dust is clearer on white. The second picture is the inside of the powder measure when empty.
I'm guessing the smell is the result of a slow reaction causing the dust to form. The 4166 has been sitting quarter full for at least 5 years.
Have you shot the cartridges that you loaded with the propellant in this state?
I have, velocity is not degraded, no misfires, no velocity spikes.
I had loaded some rounds from this a couple months ago, and I only poured as much as I needed into the measure, there was no 'powder' from the container then.
This time I up-ended the container into the measure, and the fine residue came out with the last of the powder, so it was always there, at the bottom.
That propellant suffers from dandruff. If the performance has not been affected the go for it.