The combination of two different rifle calibers in the over/under system is fairly common in Germany. It is called a Bergstutzen (mountain carbine) and typically has one barrel in a small caliber (.22 Hornet, .222 Remington, 5.6X50R Magnum) and the other in a larger caliber (6.5X57R, 7X57R, 7X65R). Perhaps one of our German members can explain how they are sighted in.