ORIGINAL: jeepkid
Oops, I guess I could have answered your question too.
The WSM out does the WM by a little bit, but not enough to make a difference. Just buy which ever one fits best. I think that the WSM ammo is probably a little more expensive, but if you reload that doesn't really matter either. Hope it helps.
The WSM outdoes the WM in advertisers hype, and amy do so in a factory load.
However, one of the constant truths about firearms that will never change is that everything else being equal, theround with the greater case capacity can always be loaded to out-perform one of the same caliber that holds less powder.
The only way a .300 WSM can out-perform a .300 WM with the same bullets is if it is loaded to a higher pressure level. I have even heard of a few cases in whichfactory-loaded .300 WSM cartridges gave hard bolt lift and stretched primer pockets. Yet, either one out-performs the .30/'06 by a significant margin, particularly with heavy bullets. If it were I, I would buy the one in the rifle design I liked the best.