The reverse of the extruder gun is a mechanism that prevents the spontaneous flow of putty or glue from the nozzle after the trigger is released. When you stop pushing on the gun without this feature, the pressure inside the cartridge continues to work for a while and the material continues to slowly flow out. The recoil gun automatically releases the pressure each time the trigger is released by moving the push rod back slightly. This immediately stops the flow of material, which prevents wastage, dirt build-up and allows for a more precise joint finish. This feature is also sometimes referred to as the "anti-drip feature".