Re: 300 Win Mag guys....
The cartridge is as capable of performing incredible feats of accuracy (especially at longer ranges) as the individual squeezing the trigger. The accuracy potential is there as long as the rifle is built with that in mind, suitable ammo is deployed with the rifle, and the shooter does his/her part.
Seriously, some of the most accurate rifles built are built around the .300WM. It is a highly capable and proven round. The biggest hurdle I see with people switching from something like a .308, .260, or some of the various 6.5mm rounds is the increased recoil which can lead to a decrease in accuracy. This is nothing that can't be overcome with proper training, trigger time and possibly a quality muzzle brake (if the competition or setting you are shooting in allows for a brake).