This was a follow on from the 1875 pattern sawback bayonet - and was issued to artillery as a multi purpose tool - intended to be able to be used in the same way the Pioneer swords were used - the initial reports on trials included cutting brushwood and planks, butchering a sheep and other useful things. It followed on the 1870 Elcho bayonet - for the Zulu War the lads would have had the 1875 model - the 1879 coming in a bit late (unless someone has a photo of the 2nd invasion crews carrying them????)
The sawback bayonets were made obsolete in the late 1890's - and I think were banned by the Geneva convention round about the Great War - the Germans carried them as "butcher bayonets" in 1914.
I have examples of all 3 types sitting here in the collection. Atb - Tim