Dg the original poster said 270 mag.He did not specify the 270 wby mag or the winchester short mag so he may have meant either.As to the accuracy thing it is far more dependant on the rifle and load than on the cartridge.As ths to comparing velocities of the various cartridges the only far way to do this is loading all to the same pressure with equal length barrels.A hot loaded 300wsm could very well produce more velocity than a milder 300 win mag load or from a short barreled rifle.Given equal pressures and barrel though the standard length mags will still produce more velocity than the wsm's.