Can't you just remove the cylinder? If I used my Ruger Old Army, that's what I would do. But man, that is a big gun. I guess I would have to walk and talk softly.
For vehicle transport a percussion firearm can have the powder and ball in it, but it cannot have a cap on the nipple.
I have a couple of the Remington 1858's and Glockgirl has an 1851 Colt--- great fun to shoot but seriously, for OC? If everyone else carried cap and ball revolvers, okay. But if you actually NEEDED to use it you'd be at quite a disadvantage:
1) Single action revolver
2) Forget about reloading. And if you wanted to, you have to carry quite a collection of crap with you.
3) At best you might have something equivalent to a standard velocity .38 special in terms of muzzle energy, unless you're hauling a Walker or Dragoon around-- which are quite heavy.
4) Damp weather--- not good.
5) Five shots, depending upon the model-- although the Remingtons allow all six chambers to be loaded because the hammer can rest in a notch on the cylinder.
6) Much more prone to fouling, jamming, failure to fire.
7) Carrying two would be better than one--- although that's true of modern pistols too!
8) Cleaning is essential, and a pain.
9) Not much in the way of a practical holster--- what sort of retention holsters are they making for those?
On the plus side--- they are pretty and the smoke smells goooood! I prefer the scent of real black powder over Pyrodex!