24" barrel at 040 grains = 0952. With a 28" barrel =1022.
difference 70 fps
10 grain net gain------------084--------------------------074
24" barrel at 050 grains = 1036. With a 28" barrel =1106.
difference 70 fps
10 grain net gain------------085--------------------------085
24" barrel at 060 grains = 1121. With a 28" barrel =1191.
difference 70 fps
10 grain net gain------------117--------------------------085
24" barrel at 070 grains = 1238. With a 28" barrel =1276.
difference 38 fps
10 grain net gain------------118--------------------------086
24" barrel at 080 grains = 1356. With a 28" barrel =1362.
difference 06 fps
10 grain net gain------------071--------------------------070
24" barrel at 090 grains = 1427. With a 28" barrel =1432.
difference 05 fps
10 grain net gain------------072--------------------------071
24" barrel at 100 grains = 1499. With a 28" barrel =1503.
difference 04 fps
10 grain net gain------------066--------------------------061
24" barrel at 110 grains = 1565. With a 28" barrel =1564.
difference -1 fps
10 grain net gain------------066--------------------------062
24" barrel at 120 grains = 1631. With a 28" barrel =1626.
difference -5 fps
Those are results using a 350 grain conical from an old Black Powder Hunting article (thanks to Rattus)