That's kind of what I thought. The army requested the 45 Colt. I wonder what the civilian popular choice was?
I didn't think Winchester made 45 Colt 1866's of 1873's so I would imagine the 44-40 would be probably pretty popular
The '73 Colt SAA was first chambered in .45 Colt for the US Army. In 1877-8, they got smart and offered it chambered in 44-40 to use the same ammo as the popular Winchester '73. These guns were marked - "COLT FRONTIER SIX SHOOTER", the only Colt product to have it's own name at that time. Source - "Shooting Single Actions" by Mike Venturino.
The term "Long Colt" came about as a result of the Army having other .45 cartridges in inventory for the top break S&Ws.
If you're into CAS, it makes sense to follow this dictum, simplifying the ammo supply. It's not uncommon for shooters to load the wrong calibre in their rifles at the loading bench. The 44-40 throws a 200 gr bullet which is more than enough for any application, then and now. Many in CAS load 180 gr bullets.
Over the years I've had all the SAA barrel lengths except the "Sheriff's Model". Currently I'm shooting a pair of 7-1/2" guns, one a Pietta, t'other a Uberti. The Pietta is a superior gun and more authentic. As for what barrel length, many find that the shorter barrel lengths offer a sharper sight picture. If you're a "point & shoot" type, that doesn't matter. The longer barrels will definitely give more velocity.
My wife shoots a pair of 44-40 Pietta's, with 7-1/2" barrels. She shoots them better than any other guns she's owned, and like me, she's gone through a few.
If ammo costs are a consideration, .357/.38 might be the way to go. The guns weigh slightly more. Almost all of the top guns use them with 'pop gun' loads that don't register on timers when shot in rifles and carbines. The bullets barely mash on steel targets at close range.
Loading the 44-40 presents one extra step in requiring case lubing due to the bottle case. If you go with the .45, the cases don't expand as well and you get case smudging, especially with BP. The cure is annealing.
You pays you money - you takes you choice.