I've read a lot of things about the zero at the long distance too. I also read that the expected use of the cap&ball revolvers was 7-28 feet in close combat.
The 1873 SAA was the one the Army asked for a pistol that could disable a horse at 100 yards thus the original 40 gr. powder charge and the 255gr. bullet.
Personally I never read anything that Colt Company said about 100 yard zero. I think the sights were low on the barrels so they wouldn't get loosened too easy and fall off. You know...tall sights have more leverage to get loosened if hit on something.
Also..if the guns were expected to be used at close combat distance of 7-28 feet and the sights were tall the guns would shoot low. The gun fired at close distance shoots low due to the sights being "up there" and the centerline of the bore is "down there" (like a scoped rifle shoots real low at real close distance.....scopes high and the bore is low).
Example...take a gun sighted in for 25 yards....shoot at a quarter sized target at 2-3 yards and aim with the sights....the gun will shoot under the small target. The same gun sighted for 25 will shoot a little low at 10 yards. The gun will shoot real close to right on at about 15 yards when sighted at 25 yards. It has to do with recoil and the height of the rear sight and perspective at different distances.
Anyway..if that's the case then a gun with a short front sight will shoot real close to dead on at real close distance. Close distance the guns were made for.
Try it....take an 1860 Army with stock sights and shoot at something 25 yards away and it'll shoot high.Then shoot it at something that's three yards away and see if it shoots high. Just don't shoot at something that's real close that the ball can bounce off of and wang ya in the forehead.
Anyway I figure that for what the guns were made for and the fact low sights don't get knocked off as easy as high ones it only made sense to have low sights on the front of the barrel.
When the Army asked for a new pistol that could disable a horse at 100 yards the 1873 SAA Colts were made in 45 Colt caliber cartridges for the heavy bullet and heavy bullets shoot higher than lighter ones in revolvers. That's why even though the sights are rather tall on an 1873 Colt they could still be aimed right at a horse 100 yards distant because the bullets were rather heavy and shot high. If an 1873 Colt revolver had little low sights like an 1860 Army it might just shoot right over the top of the horse and the rider when aimed right on at a 100 yard distance.
I'm just trying to explain that even though the 1873 was the revolver that filled the bill for the Army's need for a horse killer at 100 yards the sight is still rather tall because of the heavy bullets making the gun shoot high. Anyway I think it was the 1873 that was supposed to shoot at a horse at 100 yards. The cap&ballers were made to be used real close. Saber in one hand and the revolver in the other. They may have been able to be aimed right on a target 100 yards or 75 yards away but that wasn't a design factor asked for in the guns. They just came with low front sights because Colt made them that way from day one with the Paterson. I believe he made them that way because they would work at close range and he wanted the sights not to fall off all the time when they got bumped on things. The cap&ballers may have been used to shoot at targets 100 yards away(it's documented that Indians were shot off horses at that 100 yard distance) but that's not why the front sights were made short.
I think that was a wifes tale that just keeps getting carried along on the wind generation after generation. Made to be sighted in at a hundred yards? Heck....they didn't have much punch left that far away and Sam Colt would know that. Shoot at a horse 100 yards away and it'll sting the horse a good one but I doubt it would disable it. I used to believe that tale about the cap&ballers being designed to hit dead on at a hundred yards but...I also knew the guns were considered close range combat weapons and the Army judged the distance to be from 7-28 feet by the average soldier clamoring for his life in a whirlwind of blood and guts and screaming and horses stepping on everyone and sabers glistening in the sun as they were being swung all over the place and blackpowder smoke getting in everyones eyes and all. I've read the Army then didn't have the soldiers do a lot of practice with revolvers either. Point it and pull the trigger was about all it was for practice.
I've found that if a person fires a gun with low front sights enough that after awhile they can get really proficient at different distances with the gun that way pointing low by different amounts by instinct. That had to be the way it was done since most originals still have low front sights.
Anyway...just my opinion folks.
