It has been my understanding and experience that one can mix lots of the same canister grade powder provided that the lots have the same lot number. I'm assuming you are half way through a batch of brass and ran out of powder? I personally wouldnot have anyhesitation about opening another can of powder with the same lot number and continuing on. Might want to load a couple with the new lot first - and compare them with a couple of the first lot - maybe over the chronograph.

I don't think I would open three one pound cans of the same lot number and mix them together, though. Keep them sealed as long as possible.