wsm's overall have a flatter trajectory and disprove the long taught and accepted theory that long actions are essential for pinpoint accuracy. They also are smaller lighter rifles with far less recoil and actually more power than their same caliber counterparts. The next rifle I buy will be the 325wsm. I've read some impressive things about it.
Actually, conventional wisdom is the opposite, it says that short actions ARE more accurate, that is why a lot of benchresters are using such short actions. Makes sense from an overall rigidity sense, although I personally believe this change in accuracy potential is only noticable in the most accurate setups, and even very accurate hunting rifles aren't going to be able to detect the change.
So first benifit, slightly more rigid potentially more accurate rifle
Second, there is an assumption that a short fat powder collum is more efficient and more consistent (hence more accurate).
Third, the shorter action allows for quicker working of the bolt...but only a tiny bit faster, really, if this is an issue, consider one of the many great autoloader sporting rifles around,
Fourth, as the action is shorter, the gun is usually lighter. Hence if you are trying to shave a few more ounces on a rifle you will be hiking in the mountains with, that's a good thing.
Now, all these 4 benifits come at two costs. First, you loose magazine capacity, second, as the rims of these are smaller than the body, in theory it could be a bit more difficult to extract. Unless you are hunting dangerous game in africa, neither cost is very important to most hunters.
However, smaller lighter rifles = MORE RECOIL.
More power = MORE RECOIL
There are claims to the contrary, but simple phyiscs does not bear it out. Rather, a slightly different stock angle, and improved recoil pad is most likely the case....plus recoil is subjective, and if you convince yourself the recoil will fell less, it probably will. Still, true recoil is all about calculation of bullet weight and speed, and gun weight.
besides, these guns aren't billed as 'better than normal magnums' or at least not better by much, they are billed as 'As good as regular magnums, in a lot shorter package' Basically they are packing the same gunpowder found in 'magnum length' chamberings in a much fatter case, that is short enough to work in a short action
300 winchester short magnum is supposed to duplicate regular 300 win mag etc. T
he one exception is that the .270 short mag does outperform the 270 winchester...but then no one claimed 270 was a magnum
The second phase, the super short mags, they are duplicating the performance of standard lenght and short length cartridges, hence the 25 SSM matches the 25-06, and while the 243 SSM outperforms the 243 slightly, it matches the wildcats 243-06/ 6mm-06 etc
For the most part they succeed, except when you get into heavier bullets, then the full length versions outperform them