That will depend a lot on what charge and bullet you are using. Do a google for black powder ballistics and you should be able to find a chart that will give you some good info.

For example:
BULLET 50 caliber, 385 grain HP maxistyle, Black Powder* = 90 grains FFg






Muzzle
50 yds.
100 yds.
150 yds.
200 yds.

Ft. per Sec.
1400
1230
1103
1015
951

FootPounds Energy
1675
1292
1039
881
772

Traj: 100 yds zero
-0.75
2.5
0.0
-9.6
-27.5

You can find this in chart form on pages.sssnet.com/go2erie/muzzle.htm - 24k

Many people don't realize how much a bullet will drop after it's zero range; that's because it's already falling when it gets there.

Good Luck