44 Rimfire cal. w/7 1/2" bbl. & 1871-1872 patent dates on left side of frame. Gun has original walnut grips & mechanically gun is in good condition. The open top frontier bridges the gap between various conversions to the single action Colt Peacemaker, approx. 7,000 pistols were mfg. & this is a nice, solid example of a scarce Colt revolver.