sights are generally set to shoot point of Aim at 25 yards. as they are above the barrel you must tilt the gun up,( measure the slide to top of front sight, and slide to top of rear sight) by having a shorter front sight than rear sight. As the standard handgun round doesn't drop much between 0 and 50 yards this slit tilt up, means you are "pointing" the bullets path above the point your sights are aiming at.
http://www.google.com/imgres?imgurl...6-sTv2WG8L00gGM0vmeDw&ved=0CEsQ9QEwBA&dur=199 look at this, imagine your pistol is Zeroed at 50 yards, the bullet will continue to rise until 100~ yards. SO to hit where you want to, you need to compensate for the bullets flight path. Thus you need aim on at 50, low at 100, on at 150, then compensate for drop past 150. of course that bullet path chart isn't for .45 acp. but the logic is sound.
ok so if i understand this correctly the OP has to aim low at 50 yards because the bullet is still rising from the muzzle up to the point of 50 yards?
is this very dependent on the cartridge and barrel length?
^ excluding the rise in the middle of shooting and it hitting the ground?