Revolver, Whitney E.C.W. Percussion 22774 (AF).
The Whitney Revolver, or Whitney Navy, is, like the Colt Navy, a percussion handgun with a revolving cylinder. The cylinder can be removed and replaced with a fully loaded cylinder when all six shots have been fired, making it an ideal military weapon.
Although Eli Whitney had earlier assisted Samuel Colt with his then failing firearms business, by the 1860s, Whitney firearms were competing with Colt for business with very similar weapons. With the American West opening up, and the Civil War looming, both obtained military contracts for their Navy revolvers.
In Australia during the same period handguns were mush sought after by both the government, and those heading for the Australian gold fields. This particular firearm was likely purchased surplus from the US.