Deliberate mistake: This is a mistake which is a function of the limitation of the special effects at the time and what the censors would allow in the cinema but the wounds suffered by the Zulus do no justice to the horrific injuries that the Martini Henry rifle would have caused. The Martini Henry fired a big .45 inch soft nosed bullet that usually shattered on impact. It would have caused massive gaping wounds rather than the little red dots and trickles of blood shown on the Zulus and left many of them limbless as the bullets tore off arms and legs.
Deliberate mistake: The Zulus sniping on the defenders from the mountain are armed with Martini Henry Rifles implying they were taken from the dead at Isandlwhana. This couldn't have happened as the Zulus attacking Rorke's Drift did not fight at Isandlwhana, they were only the reserves. The looting of the camp was done by those who fought there. The Zulu snipers used old muskets.