The Zulu's tactics were a little disoriented by having to deal with the British. The Zulus feared horses, had no firearms, and had eschewed most other missile weapons, and managed to destroy Lord's Chelmford column, in part, at Isandlwhana.
I could not find the Assegai design in the "Weapons" book.
One of the notable things involved in the Battle of Isandlwhana was the problem faced by the defending troops not being positioned in the column with their own quartermasters.
The quartermasters of that day were each inventoried on each round of ammunition, cup of water and ration pack given in the field. Any such that was not given to his assigned troops was deducted from his pay!
Thus, there was great reluctance to provision the line trools when they ran out of ammo during the opening moments of the battle. According to several theorists, this was one of the real problems with the battle.
Also, unlike Roark's Drift, it was more of an open field engagement as opposed to a defensive site action (Roark's Drift being somewhat fortified by the troops there, led by Marion Chard). His use of the sandbag redoubt was a stroke of genius, frankly.
There are several excellent sites on these two engagements, just do a Google search on the names and there's lots to be had, including the "Myths of the Movie Zulu" page that has some fascinating stuff on it.
Lee Darrow, C.Ht.