Probably because most people shooting the 6mm PPC are shooting them out of high dollar, ultra-precise, tight toleranced and highly accurized custom specialty rifles, and not the typical out-of-the-box mass-produced loose-tolerance one-size-fits-all factory rifles that most people shoot .243Win out of.

I think that accuracy of a perticular cartridge has less to do with the design of the cartridge itself, and for more to do with the many other issues such as the quality and tolerances of the rifle itself, and the quality and consistancy of the ammo, and how well the ammo suits the perticular taste of that rifle.

I think that the accuracy gains that can be had by using cartridges like the .22 and 6mm BR or PPC cartridges are so small that it would likely be noticed only by the competition benchrest shooters that measure their groups by the thousandths of an inch and a .250" group will take last place. I also think that, while the BR cartridges do provide some small accuracy gains themselves, I think that much of their reputation for accuracy can be attributed to the fact that most people shooting such specialty cartridges are doing so in custom specialty rifles that are manufactured to standards and tolerances that mass producers couldn' t sell to the general populace. We' re talking about $5000+ rifles specially built with only accuracy in mind, but not a practical rifle one would tromp around the woods with.

If one were to spend the time and money to build a rifle chambered in a common cartridge like .243Win or .308Win, or whatever, to the same specs as a typical benchrest rifle, and used the same precision handloading that benchrest shooters employ, then I think you' d see similar accuracy results with whatever cartridge you chose to shoot.

So out of the three WSM cartridges I' d speculate that their accuracy, out of nearly identical rifles, would be very similar. Down range performance will vary slightly with things like muzzle velocity and bullet BC. My question is what are you going to be shooting at and what ranged are you REALISTICALLY going to be taking shot. A 1/2MOA rifle is nice, but it' s not really necessary when you' re shooting at an elk at 300 yards or less. Since you' re asking about the WSM' s I' m guessing you' re not planning on varminting so you won' t be trying to hit a 3" target at 400 yards, and probably wanting it for mid-sized big game where the vital target area is 8-16" across. If you' re only planning on punching paper then I' d suggest you go with a lighter recoiling round. The lower the recoil the better you are likely to be able to shoot it.

Mike