Re: loading for 300 win mag?
Welcome to the Hide.
You'll get a bunch more replies in the Reloading section, there is also a thread there listing specific users loads for .300 Win Mag.
With that said...
H4350 was my primiary powder.
H1000, H4831 are also good temp stable powder choices
RL-22 is another good one with 190gr and heavier bullets, it will get you higher velocities, but I don't like the temp sensitivity of the Reloader powders.