In a perfect world, cost and availability not being a factor, all my big game rifles would be built (preferably by Dorleac),with pristine Oberndorf actions. The DGR's with 1930's vintage single square bridge magnum Mausers. In the real world I willingly "settle" for FN actions, The 1950s Deluxe and the 1930s Peerless that I have on my 1939 HVA 146 are hard to flaw even compared to a Mauser.(The FN Supreme is too modern for a classic rifle.)I consider these superior to the ZG47 which is IMHO the finest commercial large ring to come out of Czechoslovakia.
When it comes to magnum length actions what are the options?
FZH currently used by Holland and Holland cost $3800 plus the cost of heat treatment. The Granite Mountain, $3700 plus an extra k if you want an integral bolt handle (standard on the FN actions). The Prechtl Mauser is beautifully made, if not an exact replica of the Oberndorf, but pricey. A (Prechtl action) Mauser 98 Magnum complete with stock, barrel, sights and the Mauser banner seems like a bargain at around $10k. Since these are out of my price range I will have to forgo the Magnum and settle for a cartridge that fits the standard action as well as my needs.
The .375H&H requires too much cutting (Bringing the 3rd safety lug into play might be an acceptable option). The 9.3x62, 9.3x66, 9.3x64 are all capable cartridges but in some African countries .375 is the minimum calibre for Cape buffalo.
The .375 "Ruger",(a word I will not speak), will be referred to as the 9.5x65.
No belt, standard length, case capacity equal to H&H, cartridge availability. Great choice.
If Mauser, Rigby or H&H had designed it it would be the perfect choice.
The .404 Jeffrey needs a 3.5" mag. An FN Deluxe mag can be milled, mostly rear, to fit with minimal loss of lower lug support. A copy of an original Jefferey is my personal preference.
For reloaders, removing 0.1" from the very long.404 neck and seating bullet to COL of 3.38" would allow loading in standard unmodified mag.Factory ammo could only be fed directly in the chamber and would have to be shortened as mentioned above to be stacked in mag.
For the.416 Rigby reduce the neck by .1" and you still have a neck longer than the .416 Ruger's. Hornady's Rigby 400gr DGXs have a 3.56" COL. Subtract .1" and you are down to 3.46 COL that can fit a standard mag with minimal removal of metal. Standard reamers and dies can be used and cases only need to be trimmed.
The .460 A square short, the 458 Sabi and many other wildcats make up in punch what they lack in pedigree and if that is not enough there is always the .550 Express.