The Porter was one of the few turret rifles ever put into serial production. Turret rifles are similar in principle to revolvers, but they is a cylinder with radial chambers (like the spokes of a wheel) instead of parallel chambers. Herein lies the potential problem: there is always a chamber pointing right back at you, the shooter. In an era of percussion guns that could occasionally chainfire, the notion of having a loaded chamber pointing at your face was less than appealing to most people. As a result, turret rifles (and pistols) never became successful designs.
The Porter, however, did see several thousand examples made. The last variant used typical percussion caps, but the first and second variants (including this second model Porter) used a quite unusual priming and firing mechanism. In addition, they and a wonderful design in which the entire side of the receiver opens up to make the action visible. This makes them much easier to understand, and very cool to look at!