A rare Colt prototype dating to 189596identified as serial number 1attempted a bold hybrid: preserve the familiar single-action manual of arms while adopting the swing-out cylinder that had just modernized Colts double-action lineup. Described as the only known Colt single-action revolver with a swing-out cylinder, the gun represents an engineering crossroads where tradition met emerging technology. Rather than a production model, it functioned as a proof-of-concept at a moment when revolver design was evolving rapidly. The backdrop was Colts recent move into swing-out cylinders with the Model 1889 Navy and the subsequent New Army and Navy series. This prototype asked whether the speed and convenience of a swing-out cylinder could be grafted onto a platform shooters already understood: the Single Action Army. In October 1896, the idea received a meaningful test; the prototype was submitted to the U.S. militarys Ordnance Board at Springfield Armory. Surviving correspondence between Colonel Mordecai and Colt vice president John H. Hall characterized the submission as being more for general style than for testing, signaling that Colt sought early feedback on the concept rather than a straight adoption decision. Even so, the board put the revolver through practical paces. Documentation notes comparisons against a Smith & Wesson single-action and timed 18-round strings to evaluate handling and throughput. Those sequences were telling: they placed the experimental Colt in direct competition with an established single-action benchmark while highlighting the potential speed advantage of a swing-out design. The timing trials also indicated how evaluators of the era balanced mechanical novelty with measurable on-range performance. Mechanically, the prototype mixed old and new in distinctive ways. The cylinder rotated counter-clockwise like other New Army models, yet it retained Single Action Army-style cylinder stops instead of the grooves typical of Colts contemporary double-actions. An additional safeguard required the hammer to be placed at the safety notch before the cylinder would swing outa procedure recorded in the 1896 Ordnance materials. These choices show Colt engineers integrating the swing-out mechanism while preserving the familiar cadence and safety cues of single-action operation. Why didnt it advance? Period materials point less to mechanical failure than to timing. By the mid-1890s, the U.S. military was moving decisively toward double-action service revolvers, while civilian buyers continued to favor the classic Single Action Army pattern. Caught between institutional priorities and consumer preference, a single-action with a swing-out cylinder had no clear constituency. The result was a singular artifact that demonstrates intent and capability without the market tailwinds needed to carry it into production. For historians and collectors, serial number 1 is valuable precisely because it bridges two epochs of Colt design. It documents how the company tested boundaries on its most iconic manual of arms without abandoning the behaviors shooters already knew. Contemporary write-ups also note imagery and references tied to auction-house materials, including a listing for a U.S. Trials Prototype SN 1 Colt New Army and Navy Revolver, which help keep the technical details and provenance in circulation. The core lesson endures: even promising hybrids can miss their moment when doctrine and demand are moving elsewhere.