Powder/bullet cominations can have a huge impact on accuracy in certain guns. In one of my revolvers, using Unique powder causes the bullets to tumble during flight. So I can have one bullet hit 5 feet to the right of the target, and the next one could hit 5 feet to the left. You just don't know where it will hit. With different powders it works fine. Then when I shoot those Unique loads out of a different gun, they work fine.
That is an extreme example though. Most combinations won't have that much difference.