砲口制动器或者后座辅助器, 炮（枪）口制退器（muzzle brake；recoil compensator）是轻兵器的枪管上或者火砲砲管上的设备的一种，俗称「防**」（但是这个称谓有误，详见下文）。这种设备的设置目的在于将弹药中所燃烧推动弹头的气体重新定向排放，如此可以减轻枪枝或火砲的后座作用（降低后座力），减少枪/砲管射击时的上扬，大幅增加射击的可控性和舒适性，尤其需要快速射击的时候。并且能使较小的载具装载更大口径的火炮。

砲口制动器在战斗时与限时射击竞赛（practical pistol）时就能够显现其重要性，甚至在大口径的火砲与战车砲上亦然；至于枪支则更无需赘言。

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.