A novel converter unit, system, and method of use with a firearm are disclosed. The converter unit may comprise a grip, pivot, and linkage. The grip is rotatably attached to the pivot, which in turn is attached to a receiver of a firearm. The linkage is in communication with the grip and a magazine release of the firearm such that rotation of the grip causes the linkage to slide toward or away from a muzzle of the firearm. The linkage and magazine release are preferably configured wherein the magazine release is not functional when the grip is angled away from the axis of the firearm. Conversely, when the axis of the grip is parallel to the axis of the firearm, the magazine release is functional.