I am exactly in agreement with you. I strongly believe in balancing the rifle to the intended game. For instance, I don't hunt whitetail with a 30-06 - much less a .300 magnum of some persuasion. It is a quarry for which one of my rifles in 6.5x57. .270, or 7x65R seem perfectly balanced. (If nothing else, such a philosophy tends to insure a broader range of choices in the gun room!)Personally I like where this is going. I prefer using a caliber that I consider commensurate for the game. My preferred caliber for deer & hog sized creatures is the 6.5 x 55 in a Swedish Mauser. Next up is the 35 Whelen. With it I would go up to Elk or Kudu. If I was expecting long range shots I gravitate towards a magnum, i.e.300 WM, 308 Norma, 338 WM. For larger animals and or DG I have number of larger calibers to choose from, like 375 H&H, 404 Jeffery, 416 Remington Mag or a 416 Rigby. The largest animal I've taken so far was a large Eland. My choice for that was a 404 Jeffery. That animal was unable to take a step forward or backward and simply collapsed in place. To the OP's point my original deer rifle was a 30-06, it was my primary rifle for about 15 years. Now I have choices. I kind of shake my head when I see folks hunting way over gunned.
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Africa, on the other hand, represents the very definition of compromise. Even if we bring multiple rifles we are all too often confronted with an opportunity for which the other rifle along on the trip would be a better choice. On a pure PG hunt it is hard to beat a .300 - .338 for such a compromise caliber. Where a buffalo or lion may be involved, then the .375 will do it all. And the nice thing about the .375, with a handful of 300 gr solids and softs, it will work on everything from Suni to Cape Buffalo.