In reality, the .300wsm case is somewhat heavier built than the .308. You'll get equal or more loadings from the WSM case over the .308 due to the thicker brass. This is where the .300wsm is able to approach the power/speed of the .300wm. The .300wsm operates in the 60,000-63,000psi range, whereas the .308win operates at a slightly lower 55,000-57,000psi range.
If you use surplus powders for the .300wsm (ie: WC-867 or WC-872, you can load the .300wsm CHEAPER than the .308.
And, all the .300wsm brass I have is FREE, as I picked it up at a public range, and from a friend who shoots a WSM.
I don't have a WSM. I do have a .300RUM. I'm using 180gr bullets I bought on sale in 2005 CHEAP and WC-860. My .300RUM cost less than my .30/30 to feed with RL15 and 150gr RN bullets........
I did have to buy my cases, but 100 is going to last me a lifetime at the rate I shoot it....
Something usually dies very quicky when it speaks....
cost is not 3x like 303Tom supposes......
But I'm not knocking the .308 either. Though I much prefer the .30/06 to all of the above.....