Just shot my little 2 incher last Sunday at 2,000 meters. Only needed a two ounce charge to reach the target with a 24 ounce ball. It doesn't take a great deal of velocity or powder to reach out quite a distance.
Back in the '60s I shot a 3" Ord Rifle with cast zinc round balls. Just guessing but we probably used about five ounces of powder. We loaded it as if it were a smooth bore and ignored the fact that it was rifled. At 1,000 meters a 50 gal drum was in peril.
The age and value of an original gun is always a consideration.