to define in operation of the spring mechanism a vector of spring force in the plane the first and second portions may be configured to form a dihedral angle in the plane the rigid bar has inner and outer surfaces the inner surface corresponding to an inside curvature of the bend the outer surface being opposite to the inner surface and the spring mechanism may include a leaf spring attached to the outer surface at only one end of the spring and disposed in the plane in a related implementation the rigid bar has inner and outer surfaces the inner surface corresponding to an inside curvature of the bend the outer surface being opposite to the inner surface while the spring mechanism may include a coil spring attached to the outer surface at only one end of the spring alternatively the spring mechanism includes a rigid plate hingedly connected to the second end and a torsion spring one end of which abuts against the second portion and another end of which abuts against the rigid plate an article of manufacture may additionally include a firearm connected to the rigid bar with a hinge such that to position the rigid bar to define a lever pivoting about the hinge in the plane between first and second angular positions in the first angular position i the spring mechanism is in contact with a.