If you fire from West to East your 1,200 feet per second muzzle velocity round will actually be moving at approxiamtely 2,500 feet per second on average around the earths axis depending on how far or near you are to the equator. If you fire from East to West your 1,200 feet per second muzzle velocity round will be moving only 100 feet per second in the opposite direction in which you fired it around the earths axis.

Sincerely,

William McCormick