There is really no one that can tell you the max range except yourself. As stated, practice and see. Remember to factor in excitement and less than optimal rests (no sandbags in the field). And also take a look at how much the wind affects muzzleloader bullets. These bullets go realatively slow and even a 10 mph wind will affect them.

FYI, my own personal max range is 150 yards. And that is after 15 years of hunting. I can't imagine ever going over 200 yards under absolute ideal conditions and a good scope.