It's okay to own a gun (without license) in Poland (so I wasn't talking about US) unless it has cartridges. Technically you could convert your antique revolver to use cased cartridges but then that's illegal and cartridges aren't that easy to come by anyway. So yeah, speed loaders are no-go, though... spare cylinders are okay.
As in, this is okay. And you can carry shittons of those cylinders. Right, the gun is fucking antique but I am pretty sure the bullets kill as well as the non-antique ones... and the guns are actually way more dangerous to the shooter (we're now assuming the shooter is a nice guy and doesn't want to shoot up a school) than the modern ones, considering you have to load them yourself and if you screw up the gun can explode in your hand, so...
EDIT:
Also, front loading revolvers were prone to jamming if you didn't flick the gun up and hit the hammer between shots
That's what you're basically doing anyway, due to recoil and the fact that you need to pull the hammer back to shoot again anyway.
And the chambers were also prone to set each other on fire, causing a misfire of all chambers.
This could be prevented by sealing the chambers with cotton, wax, or grease.
If you're going to use spare cylinders you're proably going to use something like that anyway. It's not like it would take that much longer.
So, it's not going to be like "bang-bang-bang" moving from one target to the next, they have an opening when you cock the barrel up in the air, if you know what you're doing.
It's going to be "bang-bang-bang" enough that even with the "opening", they won't be able to do anything. I mean, what do you expect people to do, if they proably have never seen a working gun before?