The following info might be of interest but confirmation of its accuracy would be appreciated.
Evert van Niekerk apparently put together his water cooled weapon in a blacksmith shop in Ficksburg, Orange Free State (OFS), operated by a certain Dan Deetlefs. The work was seemingly completed no later than 1899. During an early trial, perhaps held in Ficksburg, that carriage-mounted (and mechanically operated?) device might have achieved a rate of fire of 130 rounds per minute. The president of the OFS, Marthinus Theunis Steyn, was present at another demonstration, held elsewhere in the OFS.
The Prime Minister of the Cape Colony, Cecil John Rhodes, might have been impressed enough by van Niekerk's rapid fire weapon to offer him a sizeable sum of money. The outbreak of the Boer War, in October 1899, put an end to that idea - if the whole thing was more than a mere rumour of course.
Van Niekerk's weapon was apparently put to use in combat for the first time in May 1900 during a battle near Hammonia, OFS, between British forces led by Brigadier General Edward Yewd Brabant and Boer forces led by Commandant Cornelis Janse de Villiers. The British prevailed and the Boer had to withdraw. For some reason or other, they left van Niekerk's weapon behind. The latter, who was presumably operating his invention at the time, might have removed parts of it to make it unusable.
The British forces took the van Niekerk's weapon with them, as a war prize, and put in on display at Cape Town, Cape Colony, for some time. It was shipped to Pretoria, Transvaal, around 1930 but went missing at some point in the 1930s.
Later promoted to the rank of lieutenant (field cornet?), van Niekerk played an important role during the guerrilla phase of the Boer War which began around September 1900. The use he made of captured military equipment allegedly annoyed the British military to such an extent that orders went out that any piece of equipment which had to be left behind be buried so that he and his team would not find it. Mind you, he was also involved in a number of skirmishes.