The perfect rifle for your African or Namibian hunt is always a great debate amongst all. Many have their own opinion and has been discussed by groups many times by the fire.
The Namibia law states the following
No person shall use a revolver, pistol or automatic firearm when hunting game or use a firearm of which the bullet has an energy at the muzzle of the barrel which is lower than the following when hunting a species of game indicated there under:
Small Game:
(e.g. Dik-Dik; Steenbok; Duiker; Springbok)
Minimum caliber: .243 (or equivalent caliber in mm)
Energy: 1350 Joule
Medium Game:
(e.g. Hartebeest; Oryx; Wildebeest; Kudu; Eland and all exotic species)
Minimum caliber: .270 (or equivalent caliber in mm)
Energy: 2700 Joule
Dangerous Game:
(e.g. Elephant; Hippo; Rhino; Buffalo; Lion)
Minimum caliber: .375 (or equivalent caliber in mm)
Energy: 5400 Joule
No solid point cartridge is allowed to be used as per the Nature Conservation Ordinance No 4 of 1975 on any other species than pachyderms (Elephant, Hippo, Rhino).
I would always recommend asking your Professional hunter on which caliber to bring for your hunt. In Namibia finding most ammuniation for your popular calibers 300 Win Mag, 308, 30-06 270 Win Mag, 375 H&H and 458 Lott is never a problem.
When hunting vast open areas I would recommend your 300 Win Mag as it is a very fast rifle that can easily make your longer shots. Hunting in area with a bit more brush your slower calibers 308, 30-06 and 375 H&H is great. They are more hardy and can handle the brush a bit better than your quicker flatter shooting rifles.
Bullet selection is also vital in hunting African Game. A good soft point bullet is highly recommended and can safe you hours of time tracking wounded game. Swift A frames or Trophy Bonded Bear-claws is always a good choice. The provide excellent penetration and retains its weight very good.
Thicker skinned animals Hippo, Elephant and Rhino a 375 H&H with a solid is the perfect option.
My personal recommendation to all is to bring a rifle that you are comfortable to shoot with. As shot placement is the most important part of it all.