I'm going to be using my AR in the upcoming 600 yard rifle match. My twist rate is 1-8 which i think is plenty, i heard that you have to have a heavy grain so the wind doesn't rape your shots. Any one know the minumum grain and where i can get some? Its fun but not fun enough to just waste money on so no expenisve match ammo. worse case i'll use my 91/30 no scope but the thought hurts my shoulder.