I got the following numbers from a now deleted article "Barrel Length vs Muzzle Velocity" starting with a 30-Inch Barreled CVA .50 Caliber Accura V2 LR, Harvester Muzzleloading saboted .451" diameter 300-grain Scorpion PT Gold bullets, and BH 209 powder. Barrel was shortened in 2-inch increments and MVs measured at the same ambient temperature.
30 Inch Barrel
100 gr. 1,939 f.p.s./2,499 f.p.e.
110 gr. 2,015 f.p.s./2,703 f.p.e.
120 gr. 2,088 f.p.s./2,904 f.p.e.
28 Inch Barrel
100 gr. 1,923 f.p.s./2,454 f.p.e.
110 gr. 1,993 f.p.s./2,634 f.p.e.
120 gr. 2,048 f.p.s./2,795 f.p.e.
26 Inch Barrel
100 gr. 1,904 f.p.s./2,411 f.p.e.
110 gr. 1,951 f.p.s./2,519 f.p.e.
120 gr. 2,001 f.p.s./2,667 f.p.e.
24 Inch Barrel
100 gr. 1,869 f.p.s./2,325 f.p.e.
110 gr. 1,891 f.p.s./2,381 f.p.e.
120 gr. 1,954 f.p.s./2,541 f.p.e.
22 Inch Barrel
100 gr. 1,819 f.p.s./2,199 f.p.e.
110 gr. 1,843 f.p.s./2,259 f.p.e.
120 gr. 1,874 f.p.s./2,337 f.p.e.
20 Inch Barrel
100 gr. 1,748 f.p.s./2,037 f.p.e.
110 gr. 1,765 f.p.s./2,077 f.p.e.
120 gr. 1,787 f.p.s./2,110 f.p.e.
Sorry the tests weren't run with any other powders. I'd have liked to see those results too.