I'm glad to hear we have all these "quick loading experts" in the group. Now lets imagine your a buck private at the Little Big Horn with General Custer or on a battle line during Sherman's march to the sea. Let see how quickly you can reload while someone is shooting back at you and your stuff is not cleanly laid out in front of you in a nice quiet area.
They didn't reload, mostly. Cavalry sometimes did reload if there was a lull in the action and had a chance at a second pass, but mostly when a revolver went empty, they just switched to a loaded one, or the saber.
Most people carried at least a second gun as backup, as the chance of some cap fragment jamming up the action was quite high.
Quantrill's raiders, that employed guerrilla tactics and not formal military tactics, often carried 3 even 4 or 5 loaded revolvers, such as a brace of dragoons on saddle holsters, a brace of Navys on the belt and a Pocket or two as backup. There are reports of people carrying 5 revolvers on their person, 2 Navy and 2-3 Pockets in the belt or overcoat pockets. The Pockets were very light, but effective.
This said, as a mere exercise, I can reload my Walker with paper cartridges in under 1 minute, and I'm not that skilled nor did I practice that much.
Also, people which had battle experience in those times were pretty... cool blooded.
The XIX century infantryman had to do exactly what you said: stand ramrod straight (literally) reloading while the other side sent high velocity 1 oz chunks of lead towards them, people falling and screaming and being killed and maimed in horrible ways all around. Cavalry required even more balls than that. But perhaps these were times were people attributed far lesser value to human life, including their own.
Jonathan R: Davis and two associates were assaulted by 14 bandits, which almost instantly killed the other two. Davis was a civil war veteran, who didn't scare easily. With his two Colt revolvers and a Bowie knife he killed 11 of them, 7 with head shots, the others with the knife. Now, 7 hits out of 12 shots in the heat of a close quarter assault is pretty damn cold blooded marksmanship, let alone going after the remaining 7 guys with just a knife.
I don't doubt such a man capacity of reloading quickly and flawlessly under fire if he had the bare minimum of cover to do it.