By weight, 4 parts KNO3 and one part charcoal. I only use it in shotgun shells. The charcoal you use will determine how much fouling you get.
"Corning" is compressing the powder into hard cakes, commonly called "pucks" because a lot of us use a circular compression die. Those pucks are broken to bean sized pieces when dried, then ground up and screened to the desired size. Corning gives you a more compact powder so you can get more bang with smaller quantities by volume. Good for cartridges and short barrel pistols and such. I don't corn for shotgun or rifle powder, but I do for cartridges and c&b revolver powder. Here's some stuff you can ignore if you want to:
1. Spectracide stump remover is plenty pure for black powder. It is already powdered so is convenient. It is best to get bulk KNO3 cheaper online, but it's for value, not purity, IMHO.
2. You do not need a 12 ton press. A cheap 6 ton press from harbor freight will make you some great corned powder.
3. Homemade powder will never be as consistent as commercial, no matter what you do. You can spend an eternity trying to get it perfect but you will get to a point of diminishing returns. I weigh my powder instead of measuring by volume. I get better consistency from batch to batch that way, if I keep a standard measure of the ingredients.
4. Making a 5 pound batch is way more than most of us home brewers make per batch. You must have a huge mill. I make about 1/2 pound per batch. If something goes awry, 5 pounds is a heck of a destructive force. I wouldn't go there, but, that's just me.