Howdy
First of all, you are not going to find a replica that is absolutely dead nuts identical to an original Colt from 1873. There have been numerous minor changes in the SAA design over the years, and nobody is making guns absolutely identical to the original 1873 Colt. Subtle changes, like the shape of the ratchet teeth at the rear of the cylinder and the shape of the hand.
But you can come close. First of all, the barrels of the original 1873 Colts that were accepted by the Army were all 7 1/2" long. Shorter lengths came later. And of course, all the early Colts were chambered only for 45 Colt, nothing else.
Two things you should be aware of is that the spring loaded side latch that keeps the cylinder pin in place did not appear until around 1896. Prior to that time, the cylinder pin was held in place by a screw that angled up about 45 degrees in the front of the frame. This is commonly known as the Black Powder frame, although current replicas that have this arrangement are perfectly safe to shoot with Smokeless powder. If you study the photo posted by rcmodel you will see this style of cylinder pin retention screw. The other thing is the early ejector rod handles were of the bullseye style, not the later crescent style.
This link will take you to an Uberti model that pretty much fulfills these specifications. Scroll down to the bottom of the page and you will see what I am talking about with the bullseye ejector rod handle and the Black Powder frame.
http://www.uberti.com/1873-single-action-cattleman-revolvers
Another feature of the original Colts was the Black Powder bevel on the front edge of the cylinder. That link also shows cylinders with the Black Powder bevel. Rather than a simple bevel of even dimension around the front of the cylinder, the Black Powder bevel varied in depth from flute to flute.
The Uberti cylinder on the right in this photo has a Black Powder bevel. Compare it to the simple bevel on the front of the 2nd Gen Colt cylinder on the left.
Generally speaking, my understanding is that if a gun is imported with the two position cylinder pin, it will not have a safety device in the hammer. But I dunno if a single position cylinder pin is compatible with the Black Powder frame angled screw. You may be stuck with a D Cam safety in the hammer if you go for that model, I do not know the answer to that.
If you decide to go for that model in my link, be aware that the bright blue Charcoal Blue of that model is not very robust. It wears off easily, much more easily than a standard dark blue. I had an Uberti with that finish, and within one year of shooting the gun in CAS my sweaty palm removed all the blue off the backstrap and turned the metal a dull, battleship gray.
And of course, all 1st Gen Colts had a simple V groove rear sight, like the one on the right in this photo. Second Gens have a square groove like the one on the left. If you want 1873 authenticity, then the V groove is what you want. Which by the way is more difficult to see, that's why the Second Gens went to the square groove.
So you may have to compromise somewhere on some of the features if you want a revolver as authentic as possible to the original 1873 design. You may not be able to find all the features I have mentioned in one gun.
