Is that a VZ-52 with an AK underfolding stock, pistol grip and chambered in 5.56?
Edit: a google reverse image search yields the following.
My custom VZ-52 I shortened to paratrooper length with custom folding stock . It uses an AR magazine and it shoots .223, has a switchblade push button bayonet. The barrel was turned from a rifled blank and the three-stage muzzle brake is of My own design as with the folding stock and its mounting hardware. She was over three months in the making.It is semi-automatic.
All parts were antiqued to match the original 1953 reciever and heat-shield. She is My favorite of all My custom paratrooper rifles.
This is the original rifle.
A German 42cm Gamma-Gerät on a firing range in 1937, one of five built from left over parts at the Krupp factory after World War I. The massive gun was employed against Sevastopol during World War II, and an attempt was was even made to mount it on a Tiger I chassis to make it mobile, as it took nine rail cars to transport the gun when broken down.