I agree that the background looks South African, and the several repairs to the wheel spokes suggest this was taken well into the campaign for the Ross MG Battery. In the photo of the three soldiers next to the gun, notice that there are no such repairs. Obviously the wheels were not up to the stresses of the terrain, at least not with a load of ammo etc. on board. I assume there was space in the carriage for .303 ammo boxes, at least ten from the width of the "box" the gun sits on. That would add a lot of weight right there.