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muzzle brake

n. (context firearms English) A device placed at the muzzle of a firearm to reduce the recoil energy by redirecting the escaping gases.

Wikipedia
Muzzle brake

A muzzle brake or recoil compensator is a device connected to the muzzle of a firearm or cannon that redirects propellant gases to counter recoil and unwanted rising of the barrel during rapid fire. The concept was introduced for artillery and was a common feature on many anti-tank guns, especially those in tanks, in order to reduce the area needed to take up the recoil stroke. They have been used in various forms for rifles and pistols to help control recoil and the rising of the barrel that normally occurs after firing. They are used on pistols for practical pistol competitions, and are usually called compensators in this context.