Allan, here’s a reference for you on the ammo design problem (as distinct from the ammo supply problem) at Isandlwana, just in case you hadn’t found one yet.
“The weapon is partly blamed for the defeat of British troops at Isandlwana prior to Rorke’s Drift (in addition to poor tactics and numerical inferiority) – while the Martini-Henry was state of the art, in the African climate the action tended to overheat and foul after heavy use. It would eventually become difficult to move the breech block and reload the rifle. After investigating the matter, the British Army Ordnance Department determined the fragile construction of the rolled brass cartridge and fouling due to the black powder propellant were the main causes of this problem. To correct this, the cartridge was switched from weak rolled brass to stronger drawn brass, and a longer loading lever was incorporated to apply greater torque to operate the mechanism when fouled. These later variants were highly reliable in battle.”
