I am building the ultimate Springbok rifle based on a Remington 700 in .264 WM. Springbok are the same size and weight as a mature female Pronghorn and hunted over similar distances. I am thinking of useing the Hornady 129 SST. Am I on the right track or is there a better pill ? A 1 in 9" twist precludes the use of 140 or heavier projectiles.