Weatherby Nation

You will find very little difference in bullet performance between the .338-378 and the .340 until you begin shooting very long range, but you will find terrific difference in cost. You will pay a great deal more for loaded ammunition, and if you reload you will use around 20 grains more powder with each shot, but you will only gain about 150-200 feet per second. On paper that looks like a great deal of difference in bullet energy, but in reality you will see virtually no difference in bullet performance unless you are shooting out past 1,000 yards, and even then the difference isn't that much.

A 250 grain Partition in a .338 or a .340 Wby is unstoppable! They have a sectional density greater than a 300 grain bullet in a .375 H&H.  With a 225 grain Accubond, they'll shoot almost as flat as any .300 mag.