Something else you'll run into, especially in shoulder-fired weapons, is optic stability. That little tremor at 300 yards is going to cover a lot of ground at 3000 yards. Not to mention wind-doping and target acquisition.
Back in the late '70s we were practicing long range gunnery at Fort Knox, a place known for lots of trees, woodlines, a standard woodland environment. We put the turret of an old M48 tank in a woodline and shot it at 2500 yards with other tanks. Many crews had trouble spotting the tank turret at 2500 yards in varying conditions of shade and foliage, so we went out with a big can of yellow paint and painted the front slope of that turret eye-strain yellow. With the 10 power optics on the telescope of the M60 series, there were some crews who had problems finding that target turret.
3000 yards is a long, long way to shoot a direct-fire weapon.