I was going to comment about wearing black in the Nebraska summer heat, but Niederlander beat me to it …

I have discovered that the Natal volunteer forces, including the Buffalo Border Guard,
did not use Martini-Henry rifles and carbines … rather, at the time of the Anglo-Zulu War they were armed with Swinburn-Henry arms … which did chamber the same .577/.450 cartridge, and were
somewhat similar in appearance and operation - more so for the full-length rifles than the carbines. However, the Swinburn-Henry was actually a different action, with a modified receiver shape and a large cocking lever (used to actually set the action to half-cock or full-cock) rather than the simple "cocking indicator" of the Martini-Henry action.

As a mounted unit, the BBG were in fact armed with Swinburn-Henry carbines which (as can be noted from the above photo) were noticeably different from Martini-Henry carbines, including having checkering on the stock, longer barrels, a longer forestock without a nosecap, sling swivels, and provision for a knife bayonet. Here is a Swinburne-Martini carbine (which actually bears a Natal Mounted Police mark and number just ahead of the receiver) -
Here is a crop from the relevant plate in Osprey Men-at-Arms No. 388 "Zulu War - Volunteers, Irregulars and Auxiliaries" together with the Plate Note relating to that part of the image and also the Notes for Plate 1, with the details regarding arms highlighted. When I first looked at this image my first reaction was that the artist had done a quite inaccurate rendering of a Martini-Henry … neither rifle nor carbine … but as you can see from the above photos, it is in fact a pretty good representation of the correct Swinburn-Henry carbine -

[NOTE: the reference in these notes to a ".577" Swinburn-Henry carbine reflects a common error of "non-gun" folk, who see the full designation of the .577/.450 Martini-c cartridge and read it to mean that the firearm in question was .577 caliber.]
While I'm on a roll, as it were, here is a better photo of a Swinburn-Henry carbine knife bayonet and scabbard -
