There's a fellow who attains high accuracy with most round ball guns. His secret? None. Consistency is the key. He weighs the balls and separates them into groups according to their weight. Same patches, same lube all the time. Same powder charge of course.
It makes you ponder about the old timers who trimmed the sprue off their balls with a knife. That wasn't conducive to accuracy and yet they could hit an orange at 100 yards.