Starr Double-Action Model 1858
A very different .44 handgun from the Colts. This is a solid-frame
revolver, where the frame surrounds the cylinder, unlike the
open-frame Colts; this is a double-action revolver (where it's not
necessary to cock the hammer before firing--the trigger pull brings it
back then releases it) rather than a single. However, double-action
was an idea whose time had not yet come, as the mechanisms were not
yet advanced enough for high accuracy; subsequent models of this gun
were made with single-action.
http://armscollectors.com/mgs/starr_revolvers_week_2.htm
"The Model 1858 Double Action .44 caliber Percussion Army Revolver was the second of the Starrs produced. The Starr Arms Company of New York City, Yonkers, Binghamton and Moorisania, New York delivered 16,100 Model 1858 Army revolvers to the government at a price of $25.00 each between January, 1862 and May, 1863. This figure may or may not have included 4,950 purchased on the open market. However, Starr's contract called for 20,000 revolvers and the open market purchases seem to be over and above that total. None were purchased by the Navy Department."
The Starr DA revolver would appear to fit the description of being large caliber .44, heavy (closed frame pushed weight to nearly 5 pounds similar to the Colt Walker .44 and inaccurate)
Part of this contract (July 1862, SERIAL #6388) was issued to the 13th Illinois Vol. Cavalary
making it a western theater gun, issued to units in 1863 and 1864.
The .689 triangular base bullet was for the 1857 French Mle 1853/54/57 carbine. This weapon was supplied to the CSA from France via Mexico. It was not a US issued weapon. The French did manufacture a .689 single shot, percussion pistol that used the same cartridge! see http://forums.gunboards.com/showthread.php?t=42734 however I somehow think this was not the handgun issued to the 2nd Colorado!
Good Luck Bruce! I'm much better at finding people than guns but I'll work on it some more. The JM Davis Museum has an extensive library and research dept and its free.
John R.