JBM vs. Shooter App

[MMH]

I was comparing the results from JBM (Drift) against what the Shooter App predicts and was surprised in the difference. I was modleling a .308 cal., 180 gr. Hornady SST bullet w/ a muzzle velocity of 2500 fps & .48 G1. At 1000 yds. elevation was close (JBM - 472.2" drop vs. Shooter - 465.4" drop) but the windage (w/ a 10 mph 90 wind) was off significantly (JBM - 129.8" vs. Shooter - 102.6"). The velocity at 1000 yds. was also similar (1109 fps - JBM vs. 1122 fps Shooter). Both programs included spin drift, but not Coriolis. I also ran w/ them w/ a G7 of .25 and the results were similar.

I have checked bullet parameters used in both programs and they seem the same. Why is there such a difference in drift prediction?

 

[XBBR Shooter]

I was comparing the results from JBM (Drift) against what the Shooter App predicts and was surprised in the difference. I was modleling a .308 cal., 180 gr. Hornady SST bullet w/ a muzzle velocity of 2500 fps & .48 G1. At 1000 yds. elevation was close (JBM - 472.2" drop vs. Shooter - 465.4" drop) but the windage (w/ a 10 mph 90 wind) was off significantly (JBM - 129.8" vs. Shooter - 102.6"). The velocity at 1000 yds. was also similar (1109 fps - JBM vs. 1122 fps Shooter). Both programs included spin drift, but not Coriolis. I also ran w/ them w/ a G7 of .25 and the results were similar.

I have checked bullet parameters used in both programs and they seem the same. Why is there such a difference in drift prediction?

Because they are estimates... poo poo in - poo poo out. The spin drifts are also "hypothetical estimates". The Coriolis is shaky too.