The original Kersten system is the one seen on Merkels: extensions on both sides of the top barrel that fit into slots in the standing breech, and are engaged by round crossbolts that look much like Greeners. The system Beretta uses on the gun shown above is a variation of the Kersten, doing away with the long barrel extensions and replacing them with much shorter stubs fitted to a flat crossbolt. Some would say not as ungainly as the Merkels.