The trapdoor design was developed by Springfield Arsenal Master Armorer Erskine Allin at the close of the Civil War in an effort to update the substantial number of percussion rifles that were on hand and then obsolete. A key aspect of the design is that it was very inexpensive and easy to operate. Only 5,000 of these First Model Allins (also known as the Model 1865) were manufactured before production shifted to the simpler, centerfire Model 1866 rifles, and thus, all surviving First Model Allin rifles are very desirable. The overall design and philosophy of the conversion (remove a section of the breech, mill a chamber into the barrel, and install a hinged breechblock) remained consistent through all produced versions of Allin's system. However, the First Model has some special features such as the retention of a 58 caliber bore, a more sweeping profile to the top of the breechblock, and a spring loaded extractor/ejector assembly. The ejector/extractor was eliminated from later models in favor of less intricate and delicate extraction system. It also retains the original Civil War era sights and some of the markings including a partial "1864" date on the barrel and "1865" on the lock. A socket bayonet is included. The right side of the stock is marked "NO. 9," and the left flat has two cartouches including Allin's "ESA" stamp.

Very good with most of the refinished dark oil quenched case colors (over pitting) on the breech, mostly bright remaining surfaces with some mild pitting, mild marks and scratches on the metal and refinished wood, recut cartouches, and some slight chips on the stock. Mechanically excellent.