The flyer introducing the Lefever Nitro Special --



FWIW, Lefever Arms Co. didn't produce "sidelock" hammerless doubles. They are "sideplate" guns --



The mainsprings, hammers and usually the sears and sear springs, were mounted in the frame. Sometimes, like the Tobin Arms Manufacturing Co. doubles, the sear and sear spring were mounted on the sideplate.