"Their Martini's were new, they had ball cartridge too,
But there's scarcely a single survivor.
The British Army defeated that day
For the want of a simple screwdriver."

I believe that there is a bit of poetic licence being used here. The Sharps used at the Little Big Horn suffered from the same problem.

The "screwdriver" wasn't needed to open ammunition boxes, that would have been irrelevant if the guns were jamming, the screwdriver, or more like as not a knife blade would be used to get the spent cartridge out of the breech of the gun. Scratch marks were found on spent cartridge cases at the Little Big Horn.

Nice to see somebody in this thread giving due credit to ex-RSM Dalton who actually "master-minded" the defence of the Mission Station at Rorkes Drift.

Other misconceptions - at the LBH most of Custers men died from arrow wounds - at Rorkes Drift many of the Zulus were armed with rifles taken from the dead at Isandlwana.

The 2nd Warwickshire Regiment who fought at Rorkes Drift won because they fought in formation as trained infantry, volley fire would have solved the "rapid single fire" problems (Napoleonic times Regiments fought column with line by firing in half-company volleys - there normally being ten companies to a regiment - with a muzzle-loading "Brown Bess" Musket to those attacking in the column it was like facing a machine gun) . Had Custer's men fought in the same manner, except fore and aft, concentrating on those immediately to their front at the LBH they would have survived (the Indians with the bows would not have been able to get close enough).