The GLOCK® 19 Gen5™ MOS 9mm Semi-Auto Pistol is probably the staple compact carry firearm that all are measured by. Sized between the sub-compact 26 and the full-size 17, the 19 is a happy medium. It's the choice firearm of many law enforcement agencies worldwide and a very popular concealed carry firearm. For several years now, many have been getting their slides milled out by gunsmiths to cleanly attach a sight to their pistol. The MOS (Modular Optic System) has a slide cut out. Some still prefer a custom cut, while many prefer the ease of use with the MOS system. The G19 MOS comes with the same popular upgrades of all Generation 5 GLOCK pistols like the Glock Marksman Barrel and overall elimination of leaf springs, which have since been replaced by new coil spring designs for increased longevity and reliability.