This auxiliary cartridge was made by Frankford Arsenal and is unmarked. This was used in the end of a rifle grenade launcher to increase range. This has a steel case and was originally packed in 5 round boxes sealed in an paper envelope. The label on the envelope read: "5 Cartridges, Grenade Auxiliary M7, Ammunition Lot FA S-23, Frankford Arsenal, Loaded Aug 18, 1944". This interesting little grenade cartridge is the smallest launching cartridge I remember seeing. Free shipping.