The spare barrel for compact-length Ataman AP16 4.5 mm calibre standard length handgun. The barrel is 235 mm long. It is intended for Standard model, but it can be mounted on the Ataman AP16 Compact 4.5 mm model in order to increase the muzzle velocity. The standard barrel is 60 mm longer then the Compact model.
In case of changing the Compact model for Standard, a standard model cartridge is additionally needed.