Re: 308 bullet drop for sps tactical 20 inch barrel
That sounds about right on the velocity. Shooting any 165-168 gr. projectile out of a 20" LTR I'd get 2650 with 45.5 gr. Varget in Lapua brass. If you get the Shooter app you'll also have access to the Litz BC for that bullet (usually far more truthful than the manufacturer's numbers).
Here's the rest of what you need to know to generate good numbers. First of all, it doesn't matter one lick what the conditions are when you zero the rifle @ 100 yards. But when you want to get accurate numbers out past that, you will need to get the following as close as possible:
<ul style="list-style-type: disc">[*]barometric pressure (If you can get uncorrected station pressure, leave altitude set to zero. Otherwise, you must also input the altitude. Pressures reported on weather sites are typically corrected. They'll get you in the ballpark)[*]temperature - pretty easy to get and if it's within 10 degrees you're good[*] altitude (if using corrected pressure)[/list]
Otherwise make sure you're using the right drag model (G1 or G7) to go with the BC you enter.