As a general rule, I start with standard primers with cases from the .308 family and smaller. I start with magnum primers with anything in the WSM or belted mag families. I can go std or magnum with the '06 family, depends on the powder. Once started, I only change if something isn't working.
So for .300 WSM, I'd start with the Fed 215 magnum match primer.
There are no guarantees, all you can do is play the odds. IMHO you're more likely to be wasting powder and bullets NOT using the magnum primers than using them.
Tom
