What becomes confusing for most is how to interpret all the various rules, regulations and policies. They seem to conflict because of the hierarchy.
The IATA is an international agreement that ALL member airlines follow. (Any airline most of us are willing fly on anyway)
The TSA applies to USA flights.
The SAA policies are for ONE AIRLINE.
An airline can choose its own policies of carriage that are more restrictive. Hence, why all
domestic SAA flights will remove the ammunition from your checked bag and carry it separately. Hence, the secure and lockable case requirement for ammunition.
On the flight over (International) you may have your ammunition case inside your checked ag, but that internal (domestic) flight with the same airline will ask for the ammunition to be checked separately.
The one word that holds throughout is "secure"
IATA:
Ammunition (cartridges for weapons),
securely packaged
(only), in quantities not exceeding 5 kg gross weight per person for that person's own use.
TSA:
(8) Small arms ammunition for personal use carried by a crewmember or passenger in checked baggage only, if
securely packed in boxes or other packagings specifically designed to carry small amounts of ammunition. Ammunition clips and magazines must also be securely boxed.
SAA:
Ammunition must be packed separately from firearms in an appropriate,
secure and lockable case and although it is possible for it to travel as part of your checked baggage allowance, we strongly recommend that it be checked-in as a separate piece of baggage or checked-in at the Firearm desk.
Security staff will request the owner to open his/her checked baggage to
verify that ammunition is securely packed and that the total weight of ammunition per license holder does not exceed 5kg in weight.
https://www.flysaa.com/manage-fly/baggage/checked-baggage/special-baggage
In billc's example, his bow case may be acting as a separate ammunition container as far as SAA is concerned. Certainly, if it is lockable.