The Porter Turret Rifle was patented in 1851 by Perry W. Porter, and is a vertical turret design - meaning that it has a revolving cylinder in which the chambers are aligned pointing outward radially from the center axis (instead of all being parallel to the center axis as in a traditional revolver). There were a few turret rifle and pistol designs in this period (another well known one being the Cochran) before mainstream revolvers really solidified their dominance on the market, but they were never very successful. In addition to being complex and expensive, the risk of a chain fire causing a round to his the shooter or a bystander was worrisome to many potential buyers.
Porter made three variations of his turret rifle, and this is an example of the 2nd variation. Where the first pattern guns were made in Taunton Massachusetts, the second and third patterns were made in New York. In this pattern, Porter added a grip safety under the action lever, a pair of flash hole guards, a serpentine loading lever attached to the top of the barrel, and an improved primer feeding system, now designed to use standard percussion caps. About 350-400 of this pattern were made, of the roughly 1250 total Porter turret rifles produced.
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