Re: Suggestions for 300 mag components.
What bullet and weight are you wanting to use? And what is the primary use of the rifle- hunting, tactical?
I personally use Nosler brass for all my 300 WM loads. I have 6 reloads on most of my cases. I had to anneal after the 5th loading. The primer pockets are still good on them. I don't push my loads over max to prolong case life. Nosler cases in the 308 Win seem to get loose primer pockets after a few reloads, but I have not seen this with the 300 WM brass. Win brass is also a decent brass to use.
If you are wanting to max the case life, I would neck size only after the first firing. This will keep you from working the case head above the belt too much. With a Nosler case, I use Redding .334 bushings for .002" neck tension, and a .332 for .004" neck tension. I'd recommend .003 or .004" neck tension for neck sizing.
Powder choices depend on bullet weight. For the lighter bullets (165 grains or less) I'd recommend IMR 4350 powder (or similar burn rate). For 165-200 grains, I'd recommend R22 (or similar). For the heavy bullets 208+ grains, I'd use H1000, R25 burn rates. This will optimize the velocity. I have had good results with load development using these powders in these weight ranges.
Also, stick with the Magnum primers.
Hope this helps!
Chad