The Glock 17 Gen4 MOS 9mm semi automatic pistol is a factory milled slide cut for popular mini red dot style optics that are being mounted on pistols. Due to the speed in which the mini red dot style sights improve shot split time, or aid with failing eye sight with many shooters, they are becoming popular on everything from competition pistol to concealed carry pistols. The Glock 17 Gen4 MOS 9mm came as a response to many customers sending their slide in to custom machine shops to have is milled for their choice red dot and thus voiding any warranty left on the pistol. Glock not only milled the slide, but also includes several optics plates to fit the different thread patterns of several popular brands so that the customer is not stuck with one particular brand of mini red dot sight. The Glock 17 Gen4 MOS 9mm gives you the reliability and accuracy you have come to expect from Glock, with the innovation of faster target aquisition and shot placement with modern red dot style sights. The Glock 17 Gen4 comes standard with 3-17rd magazines where law allows.