Re: Help on Fed .308 bthp trjectory
If I'm understanding you correctly, it's the app that is giving you a <span style="font-style: italic">predicted</span> drop of 42.6" at 500 yd? If so, it is likely that at least one of your inputs was off. Something to do with input, anyhow. I would suggest you (re)check your atmospheric inputs, scope height above bore, etc.
Also, have you actually shot that ammo and determined your <span style="font-style: italic">true</span> drop at that distance? Or were you simply trying to generate a drop chart prior to shooting it at the range? Reason I ask is that under a fairly general set of conditions (70F, 29.95" Hg, 60% humidity, 1000 ft altitude, 200 yd zero, 2" scope height), JBM ballistics predicts you'd need an MV in the neighborhood of 2875 fps to get a 42.6" drop @ 500 yd. Using 2650 fps (all other conditions held the same), JBM predicts 51.3" drop @ 500 yd, which is very close to that predicted by Federal.
So have you actually shot some yet? If so, what was your actual drop? If you're trying to generate a drop table before shooting it, I'm thinking it almost has to be an input error, although it's difficult to say what it might be without knowing all of your input parameters. In any case, if you figure it out, let us know.