Howdy
I'm really enjoying the video. Mostly because even though many of those revolvers are very valuable, the owner is not treating them like works of art. He is handling them without gloves, and he is just clunking them down on the counter top. No fancy velvet cloth to cushion them.
Anyway, Indy1919a4 has it correct. The first Army contract Colts all had 7 1/2" barrels. I have been poring over my copy of John Kopec's seminal work,
A Study of the Colt Single Action Army Revolver (600 pages) and he does not state anywhere why the Army insisted on the 7 1/2" barrels. My suspicion is because most of the old Cap & Ball revolvers had long barrels, to accommodate the loading lever, the Army was just used to long barrels. Don't get me wrong, there was a lot of development work going on at Colt while they finalized the SAA design. Several different cartridges were tried, the Army ordered a few chambered for 44 Russian and 44 Rimfire as test guns. The early prototypes had gain twist rifling, but these did not stabilize the bullet very well. I'm looking right now at a copy of a document from 1882 that specifies a 7 1/2' barrel, with a twist rate of 1 turn in 16". Yes, all the early contract models were issued to Cavalry units, that is why they are often referred to as the Cavalry Model. The revolver was actually a secondary weapon for a mounted trooper, his primary weapon was his sabre. His revolver was usually carried on his weak side (the left side for most of us) with the butt forward in his holster. That way he could pull his pistol cross draw style. Trust me, it is much easier to pull a long barrelled revolver from the left side with the butt forward, than on the right side. I discovered a long time ago that trying to pull a 7 1/2" Colt from a strong side holster was next to impossible without getting my elbow tangled in my armpit.
By the way, when the Cavalry fought, they usually dismounted. One trooper would hold several horses while his mates fought standing up, or taking cover. So the weight of a 7 1/2" long Colt really did not matter too much. Neither did accuracy while bouncing around in a saddle.
This is a Colt Richards Conversion. The early examples were made by converting 1860 Army Cap & Ball revolvers to fire the 44 Colt (not 45 Colt) cartridges. Note the 8" long barrel. In 1871 the Army ordered 1000 of these.
The Army ordered several other revolvers before settling on the SAA in 1873. The first cartridge revolvers the Army ordered was a shipment of 1000 Smith and Wesson Americans, chambered for the 44 S&W cartridge. I believe this was either 1869 or 1870. This is actually a 1st Model Russian, but the American Model looked just like this, except it was chambered for the 44 S&W cartridge, which used a heeled bullet. Yes, this one has been refinished, that is the only way I could afford a pretty nice 1st Model Russian. Recent studies show that some of these were used at the Battle of the Little Bighorn in 1876.
Anyway, by about 1890 most of the original contract guns were pretty worn, so most of them were sent either back to Colt, or to the Springfield Armory to be reconditioned. Many of these had the barrels shortened to 5 1/2". Then many of them were reissued to Artillery units, hence the name. Artillery Model. Nothing to do with long barrels, it's where they were sent. Interestingly enough, many of these guns had parts mismatched when they were reassembled, so serial numbers were often messed up.
Unlike the Luger Artillery Model which did have a really long barrel.