The GLOCK 34 Gen4 in MOS configuration combines an extended barrel and slide and elongated distance between sights with the MOS concept, making it easy to mount a reflex sight on the pistol&rsquos slide without the need for a new slide or separate mounting system. The Modular back strap system makes it possible to instantly customize its grip to accommodate any hand size. The reversible magazine catch makes it ideal for left and right-handed shooters.