A pinned flash hider is a type of muzzle device that is affixed to the barrel of a rifle via structural deformation. This can be accomplished by welding, drilling, pinning, setting screws, or some combination thereof. A traditional flash hider simply shrouds the muzzle and attempts to reduce the muzzle signature by diffusing (scattering) burning gasses as they exit the muzzle. Some designs are more effective than others and they generally come in different sizes to fit different caliber weapons.
While a traditional recoil compensator vents concussion gases upward to counter recoil, a pinned flash hider diverts these gases laterally or forward, away from the shooter’s face. This feature is especially important for left-handed shooters.
A flash hider’s primary purpose is to protect the shooter from muzzle flash, not recoil. However, some designs incorporate features that also help reduce felt recoil.