Might not overlook the .284win case as a building block. Good brass from Lapua, Winchester, maybe Norma?

Hodgdon's last big bound manual cites the .30/284 as equivalent to .30-06 in terms of load data. Interchangeable...

The gunsmith columnist from Precision Shooting cited the .284 win case as being a good choice for up to .400 bullet diameter. Case has that extra .024" diameter to work with that is lacking in even an AI'ed .30-06.

So... doesn't help you if intend big5 Africa and need loaded ammo with case imprint, but if looking for recoil mgmt and enhanced precision from shorter case, you are there!

Have been wanting to build a .338/284 for a few years, but just did an AI chamber on my .338-06 so will ride that one a while longer.

Lots of great bullet choices in .338 bore. If you shoot a .357mag handgun, then the .358 bore rifle can offer you a lot of practical advantage... 9.3mm for Africa then you got the factory ammo and correctly headstamped brass going for you there.

Nice to have the integral 35deg shoulder so no fireforming cases. Nice to have shorter case w/same capacity to enable better seatng flexibility from long bullets.

.338/284 gives you the widest variety of bullets going these days with most recent designs and innovations.