So, yet another use for old powder bottles.
Mixing surplus military pulldown powders.
And I thought I was cool for taking the labels off of Hodgdons powder bottles and making bumper stickers out of them.
Huh.
Moving along........ Lemme throw my coppers in, because its late, and I'm bored.
Why don't you try contacting the manufacturers of several brands of tumblers and see how many would advise/approve of using their product to mix bulk powder?
I'm guessing it'll be a very short (like nonexistent) list.
I think if you asked anyone if they should mix powders period, regardless of what you were gonna do it in- except in an unbelievably tooled up laboratory testing environment, with proper pressure testing equipment for the results.... you'd probably get a similar result.
Making a test run for each lot of powders in 5 whole grain weight increments takes what.......... 10 rounds, 2 for each grain weight ?
If you really wanted to, you could just use 2 grain weights, something near max, and something near min- of what you ASSUME this powder is, and call it good.
4 whole cartridges- wow. The last milsurp powder I saw came in 8 Lb jugs...that 4-20 rounds not a substantial investment either way.... even if you only got it in 1 pound bottles.
You aren't making "sniperrific" ammo out of this bulk, probably degrading as we discuss this, military pulldown powder anyway.
I think mixing "hypothetically powder type A, of assumed origin and date of manufacture and decomposition" with "hypothetically powder type B, of assumed origin and date of manufacture and decomposition" gets you "hypothetically powder type AB, of assumed origin and date of manufacture, and now completely unknown decomposition and stability" Nothing more, possibly something less. It certainly does not give you a better powder "D" of known and calculated properties.
If you did this with my baking flours- I would throw you out of my kitchen, and not make you bread ever again.
I say "hypothetically" because unless its got a powder factory sealed stamp on it, thats all it is- hypothetically AA2500, or bulletpumper800x, or whatever you either assume, or deduce, it to be. I would trust a 3rd-6th party vendors' sticker/stamp application monkey about I___I <- that far. And thats assuming you trust the monkey's banana thrower of a source.
Meh, again, its only 2 coppers- YMMV.