Colt 1862 Police & Colt 1849 Pocket Cap & Ball
In 1860, the .36 caliber Police Pocket model was created, after lessons were learned from experimentation aimed at reducing the size of the .44 Colt Holster Pistols (i.e. large cavalry weapons), Colt took advantage of stronger mass-produced steel by rebating the frame of the Navy revolver to hold a larger-diameter 44/100-inch chambered cylinder, basically fitting the power of a large cavalry saddle holster-gun and fitting it into the .36 caliber Navy Model, a gun that could be carried in a belt holster. Previously, it wasn't thought that the smaller frame could handle the power of the .44 round, but the introduction of stronger metals made it possible. Learning the lessons from this, the Colt factory applied the same technology to the .31 caliber Model 1849 Pocket revolvers, using high-strength (for the time) steel for the frame, which allowed them to remove enough material to fit a larger-diameter .36 caliber cylinder which still had five shots (the alternative was to simply retain the original cylinder diameter, and create a 4-shot .36 caliber version. The stronger steels made this sacrifice unnecessary. Other changes including lightweight flutedcylinders, and a round barrel, to offset the added weight, and a "creeping" loading lever as used in the 1861 Army Model; the result was the "Police Pocket Model of 1862". The Pocket Navy was a version similarly up-sized to .36 caliber, but which retained the octagonal barrel and traditional loading lever of the earlier pocket mode. Between 1862 and 1873, Colt records document production of 19,000 of the Pocket Navies and over 20,000 Pocket Police revolvers. Relative to the .31 Pocket Revolvers, the period of manufacture was short and overall numbers were further limited by a fire at the Colt Factory in 1862 and War production concerns.[
https://www.atf.gov/firearms/firearms-guides-importation-verification-firearms-national-firearms-act-definitions-antique