I forgot to mention.
For the 300winmag my favorite powders are...
H-4831 (or H-4831sc)
RL-25
H-1000
Retumbo (for 200 to 240 grainers)
RL-33 (for 230-240 grainers)
Start with 175 to 180 grain bullets with 70 to 74 gr of H-4831. H-4831 is always accurate no matter what cartridge I load it in. (as long as H-4831 is a appropriate powder for that cartridge and bullet weight ).
Do not think that H-4831 and IMR-4831 are the same, they're not the same. Same thing goes to all the other powders that share the same numerical names like H-4350 / IMR-4350 / AA-4350 etc... There are a handful of powders like that.
And be very careful not to confuse powders with similar names like H-4831 and H-4895 etc... If you load H-4895 in the 300winmag instead of H-4831 then your rifle will be blown into little pieces and you'll be lucky if you only loose 1 eye and 1 hand along with scaring your face forever.
I remember being a little intimidated with reloading when I wanted to start. This hobby is one that rewards folk with OCD and hurts butchers.