This rare curiosity from the captured-weapons collection at the National Museum of the Marine Corps in Triangle, Virginia, may be one of the last of its kind, according to German military researcher Michael Heidler. He came across the object on a storage shelf while a curator was guiding him through the museum’s German submachine-gun holdings. But just what is this unusual artifact? Heidler’s subsequent historical detective work solved the mystery: It is an Abkomm-Lauf n/A—a small-caliber training device used by the German Imperial Navy. By inserting the barrel into a big-bore cannon, ship gunnery could be practiced using cheaper and smaller-caliber ammo, all the while preserving the bores of the valuable big-barreled guns. The Abkomm-Lauf was fashioned out of a cannibalized, obsolete Mauser Model 1871 Jäger rifle.