Reportedly, 5,000 First Model Allins, also known as the Model 1865, were manufactured in 1865 by altering existing rifle-muskets to the Trapdoor system for use with the .58 rimfire metallic cartridge, and there is believed to be 270 that were reportedly made with a 36 inch barrel (measures 33 1/2 inches to the face of the breech block) and two barrel bands for cadet use, according to "Flayderman's Guide" (9th Edition, 9A-354, 9A-355). The Model 1865 First Model Allin Trapdoor design was invented by Erskine S. Allin, Master Armorer at Springfield Armory, as a solution to converting the massive surplus of, then outdated, muzzle loading rifled-muskets manufactured during the Civil War to a more modern breech loading design. After only one year of production, Springfield shifted to manufacturing the simpler Model 1866 Second Model Allin conversion rifles, making any surviving First Model Allins scarce and desirable. This example has the shorter cadet length barrel and stock, two barrel bands, a correct "1864" dated lock, two crisp bordered script "HSH" and "ESA" (Erskine S. Allin) inspection cartouches stamped on the left stock flat, "W.B" behind the lower tang, and "US" marked buttplate tang.

Fine as period shortened, with a bright appearance on the barrel, 60% original oil-quenched casehardened finish on the breech block, with smooth mottled gray patina on the lock, some scattered light to mild freckling, and vivid case colors on the replacement hammer. Stock is also very fine with a few minor dents and dings, a small chip ahead of the lock, a minor crack visible to the right above the trigger, a small filled in circular section on top of the wrist, and crisp cartouches. The trigger occasionally sticks, otherwise mechanically fine.