If you took the container outside with you, and poured from the #1 T-7 container, it might have absorbed some moisture and that was causing your problems. Other then that, there have been many times I have shot in the snow or rain and had no problems. That would be the only thing I could think of, unless you were swabbing the barrel with too wet of a patch and not getting things dry when you loaded.

I am guessing the first part, that the pound of powder absorbed moisture is what happened. It took about five shots worth of time for it to finally suck up that moisture.