I have done so with bottles of Bull's Eye as far as having a couple of grains left in the measure. Note the bottles were bought from the same store, and probably from the same lot. I have also done this with Titegroup, and H-110 also. As far as rifle powder if there is like a half charge or so left I just pour it out into the hedge, and go buy another can.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.