Grex is almost the only way to make round balls fly really accurately A shot cup works, but with badly deformed shot you will wind up with long distance flyers.
Grex protects each round from deformation, and more importantly, will keep each ball flying in a straight line down the barrel and leaving the muzzle in a straight line. A single ball without a collar/sabot/ or other means of control, fired out of a loose bore, unrifled, or controlled in some other way, Is going to be like a BB fired down the bore of a .22 caliber airgun. Yes, I experimented with it, and it won't hit a cow beyond 70 feet.
Have any of you fired the old fashioned buck and ball rounds, smoothbore, in the old civil war loads? Black powder, smoothbore musket, etc? What does it do?