The Colt '58 Navy .36 in steel frame (this gun historically NEVER came in a .44). The .44's were the Dragoons. the pockets were .31. The belts (e.g. the Navy '58) were .36.
Then along about '60, Colt put the big cylinder .44 on the belt frame and called it the 1860 Army.
And put the medium .36 on the pocket frame and called it the 1862 Police.
These two new guns had a new streamlined appearance due to cutting away part of the frame to fit the bigger cylinder on the smaller frame.
Not too hard to figure the medium caliber (.36) on the medium belt frame, made the '58 Navy their runaway best seller. Not to big, not too small, well balanced, and Colt continued to make it right up until the 1870's because it outsold the others. Today, for the same reasons, it's a real pleasure to use, very practical choice.