I started research on this article already. The first step was to find out the pressure specs on the .416 Remington Magnum, since it has been stated earlier in this thread that the SAAMI pressure limit was about the same as for many other rounds frequently used in Africa, such as the Weatherby Magnums, 7mm Remington Magnum, .30-06, .300 H&H, .300 Winchester, .338 Winchester Magnum, .375 H&H and .458 Winchester Magnum.
The truth of this depends on how you define "about." Here are the SAAMI maximum average psi ratings for most of the rounds listed above:
7mm Remington Magnum--61,000
.30-06-- 60,000
.300 Win. Magnum------64,000
.338 Win. Magnum------64,000
.375 H&H--------------62,000
.416 Rem. Magnum------65,000
.458 Win. Magnum------62,000
The Weatherby rounds that have been accepted by SAAMI generally have a 65,000 psi rating, but some of the commercial ammo for them is slightly hotter. I could find no psi ratings for the .300 H&H, though it is rated at about 62,000 by CIP (the European ammo governing body), and the American factory standard ballistics of a 180-grain bullet at 2880 fps are well below its potential. Most American .300 Winchester Magnum ammunition is also loaded somewhat below maximum, the reason the standard muzzle velocity for 180-grain bullets is 2960 fps.
So the .416 Remington Magnum has the highest pressure rating of any of the rounds listed, except the Weatherbys, some of which have also exhibited signs of high pressure at high temperatures.
I have also heard that factory .416 Remington ammo has ben reduced somewhat in ballistics since its introduction. I will find out about this in due course as well, as I have some original (1988) 400-grain Swift A-Frame ammo coming, thanks to the generosity of a Campfire member. I'll buy some new stuff and see how it compares.
