Lefaucheux model 1835 pinfire
The Lefaucheux model 1859 carbine was a small carbine Eugène Lefaucheux made with hopes to gain military acceptance. It is a very simple design with few moving parts. It only weighs 4.5 pounds and has an overall length of 3 feet 4 inches.
There are multiple variations of this gun; some with a full metal frame, some with an automatic cartridge extractor, a percussion cap version, a double barrel version, pistols, and various bores.
This example is chambered for 12mm pinfire cartridges, has a manual extractor and a solid wood stock.
I have videos of how it works, the United States patent for it, more images and more on the blog post for it: Lefaucheux Model 1859 Carbine