We've used Black Powder for Zulu War stuff.
While it was an entertaining game, it felt nothing like a Zulu War game and had lots of individual units whizzing round the table like fireworks.
TMWWBK is a big skirmish game, not a battle game, hence the lack of flank/rear rules and so on.
The best rules for massed battles we've used are Victorian Steel and Battles for Empire (the latter is sort of based on Fire & Fury)