Ammunition companies buy unblended powder, use their pressure gauges and chronographs to determine the appropriate parameters for their cartridges. They might even order a special blend that you cannot buy, unless you have a couple of $ millions for a 90,000 lb lot.
I recently learned from a guy whose organization ran lubrication tests and investigated motor oils. Race cars will have, for example, Mobil 1 decals on the hood, but that is not the same Mobil 1 you buy. Those oils are specially formulated for that specific car. I was told by a NASCAR expert, that a bargain basement racing team requires $30 million a year to operate. I don't know if you get fed or hot water at that price level. All teams are happy to paste any logo on their car, as long as money comes with it.