I've got a Steyr SSG 69 Police Sniper Package. It has the Kahles factory 6x scope that has the ranged elevation turret. The scope is ranged out to 850 meters and is pretty much spot on at 600 with the 168 Matchking. The barrel is 24" long and I am planning to shorten it to 16.5 or 18"long. Will the loss in velocity of the shorter barrel affect the ranging ability of the elevation turret of the scope(if set on 500 will point of impact be at point of aim or low?)