For the most part, they aren't compatible. And weren't meant to be. The FED is a short action, "standard" cartridge, that is in line with a .308 , .280, or .30-06 performance wise. The .300 and .338 WIN MAGS are magnum cartridges that hold 50% more powder, and throw their bullets faster.
For the most part, unless you are hunting grizz or cape buffalo, the .338 FED, .308WIN, or the .30-06 will serve you well. Magnums don't make up for bad shooting.