Thanks to everyone for the great follow-up information.

I checked out Winchester's custom shop and see that the .404 is offered as a specialty. Price is pretty steep. But I wonder if they'll add it this year as a regular caliber in the Safari rifle? In a bolt gun, maybe going the CZ "conversion" route gets you to the same place with less expense.

The Ruger # 1 in .404 Jeffrey at NECG is tempting, but Atkinson's comment about the screw-up in chambering the M77s has me wondering whether this also happened with the run of .404 #1s? I had always seen that spec too - that a .404 has a .423 bore diameter. How hard can that be to screw-up?

FWIW, in his book, African Rifles, Gregor Woods mentions several times that over the decades the .404 Jeffrey has accounted for more large, dangerous game (LDG) than all the other big bores like the 416s and 458s. He notes that game-control officers really liked the .404 for taking out "nuisance" animals and for culling operations, whether it involved elephants, lions, buffalo, etc. He also cites the fact that the .404's 400gn load has the lowest "felt-recoil" of any of the 400-&-up bores, making it easy to shoot well for people who want to hunt LDG with something bigger than a 375H&H. Getting yourself less beat up with a .404 than, say, a 416 Rigby, would surely encourage one to practice with it more too.