You will also note that the forearm on most African rifles is relatively short. The American stock, as represented by the pre-64 Model 70, features a much longer forearm. To a great extent, this may stem from the difference in shooting preferences. The Americans tended to build a rifle meant to be shot prone, with a sling, while the British and German makers tended to build an off-hand rifle.
The front swivel on a Model 70 is far enough ahead that one would have to reach forward to contact the swivel with their support hand.
When it comes to the heavy caliber rifles, shooting with a sling was an unlikely occurrence since shots were likely to be taken at close range and often taken quickly.