Ahh, South Africa.

If this info is correct for that rifle, I'd place the date prior to about 1875 - possibly one of his first year or first few years of making guns.

By 1860, maybe 'hunters' were starting equiping with Lefaucheux-type pinfire double rifles taking fixed ammo.

It was an era of rapidly developing ctg. guns. there are always holdouts, staying and ordering what they are familiar with, ie: ML's, but the 'modernization trends' were clearly hitting the hunting fields strongly by the early 1870's.