Most likely answer, in my opinion: the shooting and/or the shooter managed to shoot better here than there, or the opposite.
However, many other items could also have a hand in different outputs of "accuracy." First thing I'd want to look at was the lot of brass and consistency of that brass from piece to piece and the consistency of the bullet pull in each and every loaded round.
It may seem like the powder is the difference, but that may not necessarily be what is happening. Of course -- maybe it is indeed the powder. Being that it seemed that each gun preferred a different powder, perhaps it could have something to do with the unlocking cycle of the pistol seemed to be better matched to the complete combustion cycle of the round it preferred?
These things are typically chased down a little better in long range rifle shooting, where on-target accuracy can be nailed down a little more clearly. Even then, it remains a very mysterious and compelling subject. Or perhaps, more like a form of art.
It often seems to be a subject with a lot more questions than answers.
Attention Brass rats and other reloaders: I really need .327 Federal Magnum brass, no lot size too small. Tell me what caliber you need and I'll see what I have to swap. PM me and we'll discuss.