It cant be different muzzle velocitys between altitude and if it is its minamal. There is no way your getting 2900 fps with only 41.1 grains of h4350 IMO ..... I have my velocity at 2800 and bc set at .6 (berger 140 vld)in shooter and I verified dope the other day at 8500 da and at 1000 yards...