Tom,
size of target in yards times 1000 divided by the size of target in mils equals the range in yards. So, a hypothetical 6ft (2yd) tall target measures 4 mils.
2 x 1000 / 4 = 500yds
Let's "assume" an AR10 .308 with a 175gr boattail (BC =.495) mv=2635, the elevation moa will be 10.75 and the round will drift 2 inches per 1 mph of wind.
That is in a perfect environment. You look to be shooting uphill in a canyon like situation. You also need to factor in the elevation, temp and humidity. I used, 500ft, 59f and 78% . Good news is that the bullet will get there in less than a sec so lead time will be minimal.
Well, good luck with that

What are you doing with a gun in space?