with that short of a barrel I'm sure you can't stay supersonic to 1000 yds probably not at 900 so plan accordingly. at one of the last 1000 yd matches there was two persons shooting an m1-a and a ar10, the ar10 could not stay supersonic to 1000 but the m1-a could with the same load so we guessed it was due to the ar10 having a 20 inch barrel and the m1-a having a 22 inch barrel. short barrels are not what you want for long range long because velocity is your biggest advantage, the quicker to bullet gets to the target the less time the wind has to mess with it. ditch that short barrel and put 26 inches instead