A stock assembly for attachment to a firearm assembly is described. The stock assembly includes a buttstock having a longitudinal conduit and a locking member; a connector tube with front and back ends slidable within the buttstock conduit between a fully inserted position and a fully extended position, the tube having a longitudinal conduit; an attachment member slidable within the tube conduit between a forward position and a rearward position, the attachment member having a front end attachable to the firearm assembly and a rear end; a spring within the connector tube engaging the rear end of the attachment member, the spring urging the attachment member toward its forward position; and locking means preventing rotation of the attachment member relative to the connector tube, while allowing the attachment member to move within the tube between its forward and rearward positions.