The Federal 215m primer was designed to fuel the Big Weatherby 378 cases. For failsafe-sure ignition of big-ass powder charges. Overly hot primers have detrimental effect on powder charge dynamics. The benchrest guys look for mild powder action sufficient for complete, but stable ignition.
Starting loads for the .338 win mag are not that much larger than .30-06. The .30-338 was at one time The Choice for longrange 30 cal matchwork.
Owning a Quality loading manual is a minimum requirement for any handloader. Sierra or Berger are the primary choices, although lots of very good info also in the Lee #2. Sierra, unless they have released #7 is about 20yrs long in the tooth, still great info; but tons of new powders they just don't care to work with...
If you are pursuing precision with low standard deviations, read up on primers and their effect on powder charge ignition.
If you are looking for hotter performance, the wildcat .338/300 win mag is right there with the .340wby and other bigboy magnums, but also allows moderate loads due to its lesser case capacity. Call it very efficient. Just have to ream your chamber and load some .300win brass.