Re: 338 federal??
338 Fed is a 338-308, the 308 is already underbore and underpowered IMO. The 338 fed is the way to stick a 338 bullet in an AR platform.
It is not really a viable long range round, it would make a great brush gun and up close "pig smacker", lots of knockdown and thump.
Compared to the 300 WM they aren't even in the same playground.