Patented in 1875, the Metcalfe device was invented by Ordnance officer Henry Metcalfe. It consists of a steel mounting bracket installed on the rifle and interchangeable wooden cartridge blocks. The blocks were to be issued pre-loaded and carried on the belt, replacing the cartridge boxes of the day. While the system never took off, echoes of it can be seen in the practice of issuing ammunition in pre-loaded "stripper clips" starting in the 20th century. Only 100 Model 1870 and 1,008 Model 1873 rifles were fitted with the device. The Model 1873 examples were never used and are assumed to have been entirely disposed of via disassembly or sales. The stock has a very good fit and a crisp "ESA" cartouche on the left flat. The front receiver ring is marked "MASS", and the top of the breechblock is marked with an additional "E". The rifle otherwise has the standard Model 1873 markings and features including the low arch breechblock and circle script "P" cartouche behind the trigger guard. The serial number falls near the accepted range for the experimental rifles.

Good as assembled. The metal surfaces have 25% of the faded original finish along with an established brown patina. There are some scattered minor marks. The stock is very fine with some small pressure marks and a few scratches and retains a dark oil stained appearance. The two click tumbler action functions fine, and the markings are clear throughout. A solid representative example of a unique U.S. Springfield Trapdoor Rifle with experimental Metcalfe device.