The .300 WSM is a Winchester Short Magnum. The short mags (there are other calibers too) are a fairly new thing on the market. To really see the difference, go to the ammunition section at your sporting goods store and compare a .300 WinMag cartridge to a .300 WSM.

One reason short mags are becoming popular is because the shorter cartridge doesn't need as long of an action, which results is a lighter and shorter rifle. The .300 WSM will perform fairly similar to a .300 WinMag ballistically (I said FAIRLY similar for you ballistics nuts), and should be quite a bit better than a .30-06 with factory ammo.

I personnally shoot a .300 WinMag, but either should do just fine for you. I believe that successful hunting shots have a lot more to do with how well you place your shot (which requires knowing your gun, ammo, and abilities) than what caliber your rifle might be.

I have had about all the the .300 mag's at some time,I have had the Norma,Weatherby,the Ultra and the WSM and the Winnie.

I was impressed with the Rem Ultra,but recoil is stout.I have had 1 winchester 300 mag and it kicked more than the Weatherby(Stock desing I think).
I have had 2 300 WSM and would not hesitate to buy another,the recoil is ok not much more than my '06 and knock down is right up there with 300 Win mag(180gr),plus it is a dream to carry almost a full lb lighter than any long action Factory magnum.
I sold the last one to a freind of mine and he loves it also,I now shoot a .338 Win mag for elk and deer,not cause I need the power but I just like the round.

I still have a 300 RUM and a .308 Norma also have my eye on a 270 WSM looks to be a smok'in plains gun.
BBJ