WW2 powder still good?

[mnguyen84]

I have a can of H4831. On the side, the disclaimer reads that the surplus powder is from WW2 and therefore, no guarantees on the content quality should be expected. While reloading some 300wsm, I decided to use some of the powder in 3 of the rounds to see how it will fair at 100 yards.

The powder was still good, surprisingly. I was able to get my usual tight groupings. This raises the questions of when does powder go "bad?"

[Bongos]

when you see a red mist or part of the powder has reddish specks clung to it, also if you get the rotten egg smell. All powder will degrade whether sealed or not. BTW the red mist is really bad for your gun, it's oily and will cling to most surface, if not cleaned, the mist will cause rust to all metal surfaces, if loaded into ammunition, and that ammo is stored, the mist can cause a bond/sealing of the brass case to the copper bullet internally, this can cause a higer than normal pressure spike. I found this out talking to Hogdgon on a lengthly phone call asking "how do we know if old powder is still good or bad"