The Nielsen Device is a type of suppressor mount that allows a suppressor to move forward upon firing and thus allow a recoil-operated firearms to cycle reliably despite the added weight of a suppressor. Popularized by Doug Olsen in the 1980s, they allow pistols to be readily suppressed without needing to tinker with spring strength, slide weight, and suppressor weight. They are not necessary or useful on fixed-barrel pistols, however.