Muzzle brakes and recoil compensators are attachments that are fitted to the muzzle of a firearm or cannon which reduces the recoil force of the gun and unwanted rising of the barrel during rapid fire, by redirecting propellant gases with the effect of countering both recoil.
There are a large number of terms, including muzzle brake, recoil compensator, compensator, recoil brake, recoil check, hybrid compensator, Mag-na-port, and more, which all refer to devices that serve to direct propellant gases upwards, outwards, or rearwards to reduce muzzle climb and recoil. These range from the simple slotted barrel of the original Mag-na-porting to the Schuemann "hybrid" system, which mates a specially ported barrel and slide with a threaded compensator for maximum reduction of muzzle rise. With the exception of names for proprietary systems, such as Mag-na-porting and hybrid compensators, and brand names such as Muzzle Tamer, the various terms are used interchangeably.
Muzzle brakes are simple in concept. One of the simplest designs can be found on U.S. 90 mm tank guns. This consists of a small length of tubing mounted at right angles to the end of the barrel. Brakes most often utilize slots, vents, holes, baffles, and similar devices to redirect and control the burst of combustion gases that follows the departure of a projectile. Another method, called porting involves ports or holes in the barrel near the muzzle that vent gas prior to the departure of the bullet. A third method involves slowing the departure of combustion gases rather than redirection. Slowing of the gases is the method used on suppressors and linear compensators. In conventional designs, combustion gases depart the brake at an angle to the bore. This counteracts the rearward movement of the barrel due to recoil as well as the upward rise of the muzzle. The effect can be compared to reverse thrust systems on aircraft jet engines. The mass and velocity of the gases is significant enough to move the firearm in the opposite direction of recoil. On the AKM assault rifle, the brake is angled slightly to the right to counteract the sideways movement of the gun under recoil.