Shooting some 9mm a little while ago I took two different types of ammunition, both the same weight. One was Speer Lawman, the other was Aguila, both 115 grain. The difference in group size was considerable...dummy behind the trigger notwithstanding, the Speer ammo would put bullets within 3-4 inches 25 yards (some of my best efforts) while the Aguila was visibly less accurate...again I am not an excellent shooter but between 4-6 inches (even with my best efforts). This was with two separate pistols, a G34 with a Wilson barrel, and a Commander frame 1911 in 9mm with a hard fit barrel. I also ran some federal 124 grain HST and it was considerably more accurate.
I understand some guns just like certain ammo better, but I've usually taken this to mean specific bullet weights.
I suspect the performance difference has more to do with the greater quality control that Federal and Speer exercise over their lines. What would that manifest as however? More consistent powder charges? Seating depths? Better crimp? Or perhaps the velocity of the Lawman (which is a hotter round) is more suited for a 115 grain round, while the lower velocity of the Aguila ammunition is less stable?