Dear Bob:
I am still "putting the story together" but here is what I
think what was going on.
Recall that after the Paterson factory went "Belly Up," Sam Colt was thrown into poverty. The one thing Colt never surrendered was his patents for the revolver. Well, when the Mexican War broke out, Captain Sam Walker tracked Sam Colt down, found him and gave him a contract from the Ordnance department for 1,000 pistols that are now known as the "Walker-Colts."
Because he had no factory, Sam Colt got the Whitney company to manufacture the revolvers for the army order. He made enough money from that one contract to set up his own factory in Hartford, Connecticut and shortly came out with an improved Walker revolver, what we call the Dragoon pistols today.
Now Colt was very anxious to sell more revolvers to the government, but the Ordnance Department kept stubbornly insisting that Colt license the Ordnance Department to make revolvers at Springfield Armory.
This Colt absolutely refused to do.
In the 1850's, with the country again at "Peace," the Ordnance Department purchased a few Dragoons but Springfield came up with the 1855 Pistol/Carbine arm.
Colt, retaliated by coming out with his 3rd Model Dragoon with an attachable Shoulder Stock AND A THREE LEAF REAR SIGHT. The Ordnance Department did find the funds to purchase some from Colt. These Dragoons were very popular when issued out to the troops.
Very quickly, after being issued out to the troops, the 1855 Pistol/Carbine proved to be a failure.
So, when the Civil War broke out, Colt had replaced the Dragoons with the Colt 1860 Army Revolver and obviously had some three leaf rear sights lying around the factory. All I know so far is that the 11th New York Cavalry troopers were issued 1860's Army Revolvers with the three leaf rear sights along with a shoulder stock. The same with a Union Cavalry unit raised in Kentucky.
Now, whether or not the M1860's with the three leaf rear sights were withdrawn or not, I don't know. that article in THE GUN REPORT supposedly has some of the answers in it. Trouble it, as near as I can figure out, the company that published THE GUN REPORT has now gone out of business and hence, one can not get back issues via mail order.
Here is a M1860 with the three leaf rear sight that was "re-worked" at Springfield Armory, probably after the war:
http://jamesdjulia.com/item/lot-201...reworked-colt-model-1860-army-revolver-32322/