"...(and if you have a remington repro just switch cylinders)...."
It was not uncommon in the Civil War era to carry spare cylinders for Colt pistols for reloading the gun quickly. When mounted, the rider would drive the barrel wedge out with the saddle horn, remove the barrel, swap cylinders, and reassemble the barrel. It was quicker than it sounded, but one had to be focused on what they were doing to pull it off.
Carrying a loaded, capped cylinder loose is not to be recomended in general. It was done in those days because it was the only practical way to reload quickly, other than carrying more guns,(which was also done) Dropping a loaded capped cylinder is in effect dropping a loaded gun that WILL quite likely fire when dropped a certain way. Perhaps even more dangerous than dropping a gun.The cylinder will most likely shoot up at some angle if/when it fires. Think about how it would have to be oriented to hit a cap on the ground, and it could be pointed a you or someone else when that happened.
Keith mentioned that some Civil War cavalrymen sometimes carried numerous sixguns into battle. I don't recall the number he stated, but believe it was up to a half dozen pistols on them and their horse. The "New York reload" isn't new.