Mason,
I'm going to post a few pictures of Colt's pattern reproduction pistols for your viewing pleasure and to help with identification.
Let's start withe what are now commonly called the "Navy" models. Colt's actually called them Belt Pistols and the Navy nomenclature may have began internally at Colt's because at Samuel Colt's initial venture a "large" order for the .36 caliber Paterson revolvers and rifles were sold to the new Texas Navy. Many of these were transferred to the Texas Rangers and the mythical status of the Colt's revolvers began. Personally I think it's because of the roll engraving that originally appeared on the 1851 that depicted a Naval battle between the Texas Navy and forces fighting for Mexico(actually British sailors fighting as mercenaries) at the Battle of Campeche. This led to the 1851s being called Navy models, the other revolvers had other scenes. In 1860 Colt's repeated the Battle of Campeche engraving on the Army model, but since they were designed to the U.S. Army RFQ and specs they were called Army Models. At that point most pistols in .44 were called "Army" models and pistols in .36 caliber were called Navy models. This carried over to the Remington models as well.
This is the original design of the 1851 (Navy), notice the square "dragoon style" trigger guard.
This is the 1851 with the more common and later rounded trigger guard.
Those both have the older loading lever linkage common to all of Colt's pistols with a loading lever until 1860. Oddly enough there was one more design in 1862 called the 1862 Navy model which was basically a smaller five shot version of the 1851.
These are the improved "Navy model" of 1861. I have shown both a more common brass grip frame and the "London Model" iron frame (so called because the London Armory put out more iron grip frames). It was an option at any Colt's Armory. The 1861 revolvers had the streamlined barrel of the 1860 Army design and the Creeping Loading Lever. Note that all of the Navy Models normally came with the shorter "Navy" style grip.
A word here about designations, there are a lot of made up terms to differentiate the different models from the current manufacturers of reproductions. You will commonly see the brass framed 1861s or even an 1860 being called a "civilian model," that is a fabrication. They also tend to call 4 screw variants of the 1860s and the 1861s "Military Models" or more commonly just differentiate the brass grip frame or 3 screw models as "civilian" models. We'll talk more about that with the 1860s.
These are the 1860 Army models. They were then what the "J" framed model 36 Chief's special was to the .38 special. Colt's put a larger cylinder on the 1851 size Belt Pistol frame. Up until that time the .44s were all Walker or Dragoon size. This was a radical departure in design partially made possible because of improvements in steel making. Look at the photos and you will see the step in the cylinder and the cut on the frame to allow the cylinder to fit. Other than the frame cut the 1851/1861 frames and the 1860 are for all practical purposes "identical."
Also note these pistols have the longer "Army Model" grip. That was a specification from the U.S. Army (cavalry) because they wore gauntlets and the smaller Navy size frames were a bit tight and short. Up until that point they had primarily been using Colt's Dragoons which have an even different grip. If you have ever handled an older Ruger Black Hawk or a first model Vaquero that grip was modeled on the Colt's Dragoon grip. While it is shorter than the Army model grip it has a larger girth. Because of the frame size Colt's was limited to changing the girth too much and the added length satisfied the Army board testing the new pistols.
The bottom 1860 is called by some the "Civilian Model" because it doesn't have the cutouts on the recoil shields or the two extra screws per side to facilitate the attachment of a shoulder stock. Colt's actually later dispensed with the two extra screws and in some cases you see frames with and without the recoil shield cuts. So there are "3 screw" models with and without shield cuts. The stocks weren't very popular or very practical. They seemed like a good idea but can be dangerous to use. There is also an all brass grip framed version some call the "civilian brass frame Army model," I guess that's okay since the models provided to the Army appear to all be iron back strap models with 4 screws and the shield cuts. There were some different variants submitted for evaluation, but for the most part the martially marked 1860s are like the first one shown above.
Since I mentioned the 1862 Police that had the creeping lever I wanted to show that to you as well. Remember I said earlier that the 1860 was sort of like the S&W 5 shot small frame revolvers? This one is really a 19th century analog to the M36 S&W. They took an 1849 frame (.31 caliber) and added a 5 shot .36 caliber cylinder to it and used the rebated concept of the 1860 to make it fit. The '62 Police had cylinder lightening flutes but the 1862 Pocket Navy looked like a cross between an 1851 and an 1860. I guess it is the "precursor" to the "1851" .44 caliber pistols that Pietta has been producing. I am not a fan of the 1851 in .44 caliber because it is blurring the nature of a reproduction. I know there will be those who will opine that most of our modern pistols are not in the correct original calibers, that is true but they aren't an imaginary kludge of designs that never existed until Pietta got wild hair... The caliber divergence is just the product of necessity when it comes to available ammunition.
These are the 1862s which are both 5 shot .36 caliber cylinders on the smaller 1849 frame originally in .31 caliber
have fun,
Mako