I pity the poor paying customer who has to obtain info in this regard.
Eventually spoke to a lady by name of Izanne  Kotze (Tel 978-6331) who appears to have all the info, but here it is as I understand it:

Assuming you are travelling economy class, you are limited to checked baggage of 20Kg. Excess is charged at R23 per Kg. Your sporting goods (including ammo) can be weighed as normal baggage, and charged at this rate if total is over 20Kg, OR you can have your sporting equipment, including ammo weighed separately to your other baggage, and be charged at R16 per Kg from 1Kg up. It then does not form part of your 20Kg baggage limit, which is then available for your normal luggage.

Total weight of ammo is limited to 5Kg regardless of which of the above methods of checked baggage  you follow. - per regulations regarding transportation of dangerous goods.

Process as follows:

You are also allowed one piece of hand baggage which is over and above your 20Kg limit- do not put anything related to shooting in this bag!

Trust the above helps, but we can talk further on Saturday - meeting still on for 10:30?
Best Regards.
Hein Krüger
Quality Assurance Auditor
South African Airways Technical
T  27 11 978-5105
F  27 11 978 3106
C  27 83 460 6007