Re: 338 federal
The .338LM and .338Fed are NIGHT and DAY different in terms of their capabilities and intended uses.
The 338Fed is a short-to-medium range hunting, brush-gun, larger game load developed by Federal in conjunction with Sako using necked up .308 Win brass. It has found some favor with hunters given that it packs a nice punch in a lightweight, short-action package and one that will fit the magazine restrictions of the semi-auto, large-bore AR platform rifles (Armalite AR-10, DPMS LR-308, etc.).
What specifically did you want to know about it aside from something like that? As for ballistics/reloading data, Google is your friend as there is a bunch of readily available info on this round already out there.