Theres more to recoil than weight of gun bullet weight, and bullet speed. I can cite an example of two guns of equal weight shooting identical cartridges at equal speed yet having dramatically different recoil. In the first case you might have a custom 18" barreled 308 bolt action rifle with an overall weight of 9lbs. In the second case you have a 18" G3 rifle weighing 9lbs. The G3 will have greater recoil than the 9lb bolt gun. I believe the locked bolt on the first rifle provides more initial inertia and resists acceleration into your shoulder, while the quickly unlocking bolt on the G3 provides little initial inertia and thus adds to the shoulder impact. This is not even to mention the effect of muzzle brakes etc. This is all a different discussion, however I do believe that my 270wsm has significantly less recoil than an equivalent 7 mag. And my rifle is a pound lighter than average. Something is in play, not being obvious.
The 7mm mag does have 15% more powder than the WSM (both have about the same max pressure). The momentum from the products of burnt powder has to provide a significant amount of the recoil (acting like a rocket nozzle), otherwise muzzle brakes wouldn't work.
To keep the thread on topic, I'll say that my most powerful 30 caliber is currently a 30-06. As someone who hasn't played with the 30 caliber mags yet, if I were going to buy a magnum I'd go with the 300 WSM. My thinking is as follows:
1. With the light bullets (copper) I shoot the 300 WSM matches the 300 win mag. Why not do the same thing with less powder (recoil) if I have that option?
2. A 24" 300 WSM barrel is effectively 1/2" longer than a 24" 300 win mag barrel (because barrel length is measured to the bolt face, but the pressure acts on the bullet from where the powder meets the bullet). Combined with the shorter action I figure a 300 WSM should be an inch shorter and quarter or half a pound lighter than an equivalent 300 win mag. I also like a short LOP, so short bolt throws are good to keep the end of the bolt away from the tip of my nose.
3. The 300 WSM appears to be about the fourth most popular 30 caliber on midway's website (behind the 308, 30-06, and 300 win mag). Heck, the 300 WSM even has more loadings available than the 30-30. I'm personally not worried about ammo availability in the future.
4. If I ever get into reloading, it seems like the WSM would be better (less powder and maybe longer brass life due to the lack of a belt?)