a part that can be attached to the handle of a gun that makes it able to fire repeatedly more quickl

中文解释

撞火枪托（一种将半自动步枪改装为类似全自动步枪的装置，方便连续发射子弹） The Department of Justice announced plans to restrict the sale of bump stocks. 美国司法部宣布了限制销售撞火枪托的计划。