Re: Large Magnum rifle powder recommendations
No powder will work well with all those. The 338-378 throws the biggest curve which needs super slow stuff with H-870 being the best. Retumbo will work in it but not as well and will work in the 340 wby but not as well as powders just a little faster like 7828. The large cartridges you listed need something faster. You are trying to do the impossible and will defeat the purpose of your chosen cartridge with the wrong powder. Of all those listed all you need is the 338-378 wby which will significantly outperform all the others and by far the best. Unless you go to Africa with caliber minimums.
Predictions are difficult, especially when they involve the future