Muzzle brake
A muzzle brake or compensator is a device that is affixed to the muzzle of a firearm to redirect propellant gases with the effect of reducing both recoil of the gun and unwanted rising of the barrel during rapid fire. Muzzle brakes are very useful for combat and timed competition shooting, and are commonly found on rifles firing very large cartridges (often big-game rifles), as well as some artillery and tank guns. They are also commonly used on pistols for practical pistol competitions, and are usually called compensators in this context.
Muzzle brakes are simple in concept. One of the simplest designs can be found on U.S. 90 mm tank guns, which consists of a small length of tubing mounted at right angles to the end of the barrel. More typically, they consist of a tube "fit over" the end of the barrel, pointing into the same direction as the barrel. Slits or holes in the tube are angled towards the rear of the gun. The working principle is the same: During the brief period in which the projectile has left the barrel, but not yet the muzzle brake assembly, the released gases hit the inside "front" of the muzzle brake tube, and pushing it, and thus the gun as a whole, forward. The holes in the muzzle brake direct the gases sideways with a rearward component, countering the recoil. (This effect very much resembles reverse thrust systems on aircraft jet engines.)
There are advantages and disadvantages to muzzle brakes on firearms. Despite manufacturers claim recoil reductions of 50% and more, that is really physically impossible. However, in combination with the reduction of lateral barrel movement, the shooter may perceive a 50% recoil mitigation. Other advantages lie in the reduction of the barrel's lateral movement. As the gun moves only little off target, quick re-aiming for additional shots is much easier. This is relevant particularly for fully automatic weapons. The other effect is increased accuracy. The propellant gases rushing past the projectile just as it leaves the barrel can cause it to be deflected; a well designed muzzle brake diverts these gases away from the bullet at this moment, thereby reducing the deflection. Certain types of muzzle brakes slightly stabilize the bullet at this juncture and noticeably decrease shot to shot deviation.
The disadvantages of a muzzle brake also originate from directing the propellant gases off the direction of fire. First, as the weapon's noise is directed sideways as well, guns with muzzle brakes sound significantly louder, particularly to the sides. The second effect is relevant to the military: spreading the hot propellant gases sideways results in a much larger muzzle flash. Especially at night the brighter flash is more likely to reveal the firing gun's position. The flash intensity depends of the type of muzzle brake, yet effective suppression is only achieved with military flash hiders of the Vortex design.
Muzzle brakes on both small arms and artillery pieces can also cause escaping gases to throw up dust clouds, impairing the firer's visibility and revealing his position to the enemy. Troops often wet the ground in front of antitank guns in defensive emplacements to prevent this.