Got the following reply to my query on another forum.
Lyman Black Powder Handbook & Loading Manual page 270 for .58 cal. RB, from a 32" barrel, 1:48" twist.
Pyrodex RS
70 grns=1231 fps
80 grns=1317 fps
90 grns=1378 fps
100grns=1439 fps
110grns=1538 fps
120grns=1638 fps
Thats more like it! For a minute there I thought I might need to trade in my Zouave for a slingshot.
