The original reports were that the weapon was a handgun and the distance was over 100 yards. It could have been a pistol caliber carbine.
A .22 caliber rifle can be construed to be a pistol caliber carbine. That cop that got shot in the face, would have had more damage from a pistol caliber carbine.
Shooting a piston at a crowd at 100 yards misleads us into thinking the shooter was aiming at THOSE two cops. He was shooting at a row of cops.
Billy Dixon gives is the same problem. He shot an indian off his horse at a range of one mile and everyone was amazed. We forget he shot at a group of Indians on horseback on that ridge. His target was a square 12-14 feet wide and 7 feet tall. Hitting something inside that square make us think that was the deliberate point of aim.
This Ferguson marksmanship is not particularly remarkable.