When I ordered a double rifle from Krieghoff in 1970, it was a Trumpf, a boxlock O/U model with ejectors. At the time, no rimmed classic African cartridges were being manufactured, so I decided on .458 Winchester Magnum, with a second barrel set in .375 H&H.
I received the rifle shortly before my first African hunt, and was dismayed to discover that the .375 H&H barrels defied the extractor, and fired cartridge cases had to be tapped out through the muzzle, not an easy job. As I was planning on being in Germany for several weeks prior to my African trip, I decided to deliver the rifle back to Krieghoff in person. I don't know to this day what they did to it, but it extracted and ejected flawlessly afterwards.
However, it left me convinced that rimmed cartridges were the only way to go with a double rifle, and since .375 H&H Magnum Flanged had become available through Bell, I designed a cartridge which was basically the .450 Watts with a rim. I had a reamer made up for it, had a barrel fitted to a Ruger No. 1 action and chambered with it, and proceeded to fire-form and test the cartridge. As soon as I was satisfied with the performance I was getting, basically .450 NE velocity with a 500 grain bullet, I loaded up a 50 round box of ammunition and sent it and the reamer to Krieghoff with instructions to build a double rifle around it. This they proceeded to do, and in due course, I received it. It has performed fully up to expectations.
I continued to use the original rifle, but only once each on elephant and buffalo (the .458). I eventually took lion and leopard with the .375 H&H barrel pair, but only after it had performed flawlessly on plains game and in practice at home. Most of my thick skin DG shooting was with a bolt gun with a cartridge, also designed by me, called the .505 SRE, which duplicated the performance of the .500 Nitro Express.
Interestingly enough, even when I was having the problem with stuck cases in the .375 H&H, the rimless extractor never failed. In fact, the extractor threatened to bend before the spring loaded portion of the extractor gave way.
I see no particular problem with a .30-'06 double rifle, provided you don't plan to use it for dangerous game, but for DG, give me a rimmed cartridge in a double rifle every time.
Here I am with the Krieghoff and a 94 pound single tusker taken on the last day of a five week hunt in Kenya:
