The Walsh design is interesting. But I am not yet sold that the forward charge wouldn't frequently set off the rearward charge. However, let's just for the moment take it at a given that it worked and didn't set off the rear charge at the same time for the purposes of the below discussion. I am wondering if perhaps a regular reproduction black powder revolver might be modified to do similar at a minimum of cost and bother.
I invite comments and let's explore this.
First for any BP newbies, I'll mention multiple projectile loads that can be loaded into the chambers of regular black powder revolvers.
If you have a very long cylinder such as with the Colt Walker repros, you can easily load like this. First load a charge and seat your ball on top of it. Then put a cardboard spacer or even a felt wad on top of that ball and load another ball on top of that. The cardboard or felt spacer is so the two lead projectiles won't be driven to stick together when they are forced against each other when they are pushed out. I have heard of people using buckshot balls to do this with also.
If you are using a shorter cylinder, say a 1851 or 1860 Colt, you might have to use .38 caliber or .45 caliber wadcutter lead projectiles and shorten them a little for them to both fit into the cylinder. But the idea is the same, two strikes on the target for each chamber shot fired. I have loaded two shortened .38 caliber wadcutters like this in a .357 cartridge case too.
Now let's explore how superimposed separate loads in single cylinders (Walsh/Roman candle style) might be made using standard BP revolvers.
I don't like the idea of the split hammer (essentially two hammers) and two triggers on the Walsh revolver. Too complicated and too easy to function both triggers accidentally at the same time.
Instead I am wondering if a cam such as used in derringers could be used so that one time the hammer is pulled back it is in a position to hit one of two nipples over one chamber, then when the hammer is pulled back again it it cammed to change its position to hit the other nipple for the same chamber. That would eliminate the need for two hammers and two triggers.
The cylinder would be kept the same as the Walsh cylinder having a flash channel going from one nipple that enters the chamber at the halfway point.
The other flash channel entering the chamber at its rear as in normal BP revolver operation.
The trick would be, how to modify a standard BP revolver so that its hammer cams into a different position to fire each successive nipple. I am also thinking of having a movable striking head on the hammer. So that you would first fire 6 shots normally, then move that (spring detent held) hammer head to where it would strike the other nipples and fire six more shots that way.
Sure would be an easy way to do it by only modifying a standard BP revolver to have a movable striking head on the hammer, and replace the cylinder with a Walsh type superimposed load cylinder. Yes you would have to move the striking head of the hammer after the first six shots so it would contact the nipples for the next six shots. But that would be better than two hammers and two triggers as in the original Walsh. Wouldn't take but half a second to move the hammer head and then you have six more shots.
Then you could actually load two projectiles in each superimposed load like I described earlier, and have 24 strikes on the target for twelve shots.
Purely academic, I'm not thinking of building one. Actually if I was going to build something like that, I'd switch to this idea instead, which could be done with a percussion or cartridge revolver without any permanent modification to the revolver, by simply replacing the cylinder with a gear on the cylinder pin and adding the chain held chambers.......
That would be really cool on a double action revolver, percussion or cartridge.
Just don't ask me how you would holster that. Lol.