The hole was for a little wooden plug that was a gov't property mark.
Don't know about Africa, but a lot were sold in North America, given how often they turn up. Could well have been marketed in Africa.
There were a large number of obsolete large caliber military rifles turned into cheap shotguns in the later decades of the 19th century and first few of the 20th.
Tabatieres, like this Zulu, Gras rifles, 1871 Mausers, Rolling Blocks were all converted, usually in Belgium. The Geha shotguns are the same sort of thing, but done post WW1, using G98 Mausers. I have the remains of a M91 Mosin Nagant converted into a single shot .410 shotgun. At the time, large bore rifles weren't as saleable as cheap shotguns.