Firearms have a lower frame including a trigger and a grip, an upper frame including a barrel and a bolt, and a magazine receptacle configured to receive a magazine and positioned between the upper and lower frames. The lower frame and upper frame may each have forward portions pivotally connected to each other to form a pivotal connection. The pivotal connection may be operable to pivot on a horizontal axis transverse to the firearm. The upper and lower frames may be movable between an open position in which the upper and lower frame are angularly separated from each other and the magazine receptacle is accessible for removal and replacement of a magazine, and a closed position in which the magazine is closely received between the upper and lower frames. The magazine receptacle may be laterally open on both sides of the firearm.