But mixing them is supposed to be a NO NO.
They might not be exactly identical.
Don't even mix different batches of the same powder.
There might be some variance, batch to batch.
Can't ever be too careful when messing with gunpowder.
It doesn't matter if they aren't identical, mix it well and it will blend in and still be different from other lots... just like the lot he has now is different than what he's going to. Mixing together now and working up now is fine.
Ball powders are pretty consistent, I routinely back mix the last of an old lot with the new and have not seen a change in velocity.
Yeah. I don't shoot over a chronograph but have never noticed a change in accuracy or pressure signs going from lot to lot.