Glock 27 Gen4 The GLOCK 27 Gen4, in .40, introduces revolutionary design changes to this small, light, accurate, and powerful pistol that so many law enforcement agencies have issued as their offical backup weapon. The Modular Back Strap design of the G27 Gen4 .40 Caliber lets you instantly customize its grip to adapt to an individual shooter's hand size. The surface of the frame employs the new scientifically designed, real-world-tested, Gen4 rough textured technology. Internally, the new GLOCK dual recoil spring assembly substantially increases the life of the system. A reversible enlarged magazine catch, changeable in seconds, accommodates left or right-handed operators.