Hair Trigger
US Veteran
I always pour the last of a can of powder into the next and mix very well by shaking and rotating vigorously.
This is what I also do. By the time I get to the bottom of a powder can, there's less than what it would take to make a single round. I can't see how 30 grains of powder of one lot could affect 7000 grains (one pound) of another lot, when they are the same type of powder.