The major drawback of any muzzleloading firearm has always been that you only get one shot before needing to reload. If you could get off three shots in a minute, you were doing really well.
One way to get more out of your muzzleloader was to adapt it for superposed charges. That is, multiple loads of powder and projectile stacked on top of one another. In some primitive examples, all of the superposed charges would ignite one after another like a Roman candle firework. Other examples offered a little more control.
The maker of this percussion rifle isn’t known, but he came up with an innovative device. An extra attachment was added at the front of the standard percussion lock. A spring positioned a hammer extension over a second cap and cone, which was held in place with a second trigger-activated latch.
In order to fire the rifle safely, the extra attachment on the lock must be discharged first. After firing the first bullet, a clear path of ignition for the second charge is now available. Firing the gun in the opposite order is a self-correcting error, as there will be too much pressure in the barrel and the gun will most certainly explode.
To fire the second shot, simply pull the secondary trigger to release the extra attachment, getting it out of the way. Then, cock the hammer as normal and pull the trigger. This will drop the hammer, igniting the cap on the traditional cone.
Was it the best solution? Probably not; it certainly did nothing for the aesthetics of the gun. Nonetheless, it was indeed a working solution to the single-shot dilemma.