Drawing in an US Intelligence Report from January 1945. The barrel of the examined ZfG had rifling with right-hand twist. Certainly it was a reworked old machine gun barrel.
A German machine gun for static defense, Zf.Ger.38, c.1944. It was fired by a trip-wire. A bullet-cutter could be fitted to the muzzle to fragment the .31-inch (7.92 mm) projectile, thus giving the effect of a shotgun pattern. From the contemporary technical report.
The Zf.Ger.38 is a machine gun of German origin. The weapon is a blank firing training weapon also used for static defence. When the Allies examined the weapons discovered in the German Reich after World War II, they came across a device which was classified as a “spring gun” or “trip wire activated static defense machine gun”. It was a practice device with the name “Zielfeuergerät 38″.
The Zf.Ger.38 is a blowback operated magazine fed training weapon, using 7.92×57mm wooden bullet blanks. The simple construction was sturdily implemented, and reduced to the most necessary functioning parts. The device functions as a blowback operated weapon with unlocked bolt in full automatic mode only.