I doubt it's a good idea to fire at 1200+ m with a convential rifle bullet at all. There are 12.7 mm rifles for such huge distances.problem with sniping rifle is that 1500 meter or beyond.accuracy drop due to cross wind.
this problem particular in long range sniping in afghanistan theater.
US army is developing new gen. of sniping rifle.with new gen. laser range finder, not only provide range but also cross wind.
I doubt it's a good idea to fire at 1200+ m with a convential rifle bullet at all. There are 12.7 mm rifles for such huge distances.
I just hope they won't try to equip every platoon marksman with it. Should be a cool thing for special forces, though.