Back in the day Samuel Colt made both 5 and 6 shot .31 pocket size which today we call the 1849. Most were 5 shot. Some were 6 shot.
As time went on, Colt was using better steel (imported from England, Bessemer type steel. This made a 6 shot pocket model .31 strong enough. It also allowed putting bigger calibers on smaller frame, and Government asked for a .44 medium size gun (today we call it the 1860 model). Stronger steel made this possible in 1860.