The Metcalfe device was invented by Ordnance officer Henry Metcalfe and patented in 1875. 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. 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 nearly entirely disposed of via disassembly or sales and many of the experimental components were destroyed. Some were later reassembled using the original Metcalfe parts making rifles from the original serial number range complete with the device and block incredibly scarce. The stock has a very good fit and a crisp "ESA" cartouche on the left flat. The rifle also has the other standard Model 1873 markings and features including the low arch breechblock and circle script "P" cartouche behind the trigger guard. The latter has "J.C." just ahead of it. The serial number falls in the estimated range for the experimental rifles from 1876. The cartridge block is the type IV style from May 1876 and holds eight cartridges. See the pictures on page 58 and 59 for a matching rifle and cartridge block from the same serial number range.