Efficacy, now there's a word I was not expecting to see on the BP forum.

Anyway, I know that certainpowders, once opened,do lose power over time. Humidity is especially bad for certain powders that are "sugar" based.

I don't know about 777, but I'm sure others here do.

Right now I am shooting some Pyrodex that is several years old, but only opened last year. I use some plastic wrap under the lid and screw it on tight for storage. No issues with power yet.