Are you talking about tactical or for hunting? It takes a hellova shot to make a 1,200 yard shot. Not many are that good. Also a .270 don't make for a good tactical round due to lack of good bullet selection for that purpose.
Originally Posted by tuckinauster
Depending on your particular load the bullet should stay super sonic, and thus stable, out around 1200yds with enough energy to ruin your day.
Heres a look at what I'm shooting for when I start loading for my .270:JBM - Calculations - Trajectory