Given your username,I would think that you would know better than to use manufacturers published data to compare velocity potentials of these two cartridges.Anyone with any amount of experience with weatherby and remington should be well aware that remington loads their factory loads quite mild while weatherby factory loads are quite hot.The fact is that the case capacity of the 300/338 ultramag actually exceeds the case capacity of the 300/340wby and the result is that the 300/340 ultramag actually has the potential to produce slightly more velocity if both are loaded to design pressures.