I have not read through all the posts but the question of reloading in the old west got me thinking. In something like the killing of Wild Bill or Jessie James it was one shot and done.
Other fights involved a few more shots, Dallas Stoudenmire's "four dead in five seconds" in 1881 or Commodore Perry Owens' fight at Holbrook in 1887 (where he shot 4 at close range with a Winchester 1873 in less than a minute) or even the OK Corral fight come to mind. In these cases quite a few shots were fired but things were generally over before there was a need to reload. In the one example I have mentioned where its know than a gun was fired dry, Doc Holiday's shot gun, the fight was still underway so Doc transitioned from the empty shotgun to a loaded revolver.
There are cases where gunfights went on for hours or even days. For example When Nate Champion and Nick Ray were surrounded and killed during the Johnson County War in 1892 the shooting went on for hours before the cabin was fired. The siege at Alex McSween's house in the Lincoln County war lasted five days before the house was fired. In these cases all combatants must have reloaded. Participants in battles with Indians are also know to have fired very large numbers of rounds, the Wagon Box Fight of 1867 (which lasted 5 hours) and the battle of Adobe Walls in 1874 (which lasted 3 days) would be examples, though there are many others.
The conclusion to be drawn from these examples is that reloading, or not reloading a shotgun, rifle or revolver was not causally related to the nature of the old west, it was determined by the nature of the fight, just as it is today.
As far as reloading shotguns goes, while I know of no specific examples where it was done, I know that express companies provided spare ammunition to shotgun guards in case they needed to reload. There is a photograph in one of R.L. Wilson's books of a wooden block holding shotgun and revolver ammunition provided to guards by Wells Fargo. Even if reloads never happened, having spare ammunition on hand must have provided a psychological boost to express guards as no one feels good about heading into a fight short of ammo.