Several modified versions of the Glock 17 have also been introduced. The Glock 17C incorporated slots cut in the barrel and slide to compensate for muzzle rise and recoil. The Glock 17L incorporates a longer slide and extended barrel. Initially, the Glock 17L had three holes in the top of the barrel and a corresponding slot in the slide; however, later production pistols lack the holes in the barrel. The Glock 17MB is a version with ambidextrous magazine catch. Glock pistols are designed with three independent safety mechanisms to prevent accidental discharge. The system, designated "Safe Action" by Glock, consists of an external integrated trigger safety and two automatic internal safeties: a firing pin safety and a drop safety. The external safety is a small inner lever contained in the trigger.
