<P> The polymer frames of third - generation models can be black, flat dark earth, or olive drab . Besides that, non-firing dummy pistols ("P" models) and non-firing dummy pistols with resetting triggers ("R" models) have a bright red frame and Simunition - adapted practice pistols ("T" models)--a bright blue frame for easy identification . </P> <P> In 2009, the Glock 22 RTF2 (Rough Textured Frame 2) (chambered in . 40 S&W) was introduced . This pistol featured a new checkering texture around the grip and new scalloped (fish gill - shaped) serrations at the rear of the sides of the slide . Many of the existing models became available in the RTF2 version, including the 31, 32, 23, 21, 19 . Some of those did not have the fish gills . </P> <P> At the 2010 SHOT Show, Glock presented the "fourth generation", now dubbed "Gen4" by Glock itself . Updates centered on ergonomics and the recoil spring assembly . The initial two fourth - generation models announced were the full - sized Glock 17 and Glock 22, chambered for the 9 × 19 mm Parabellum and . 40 S&W cartridges, respectively . The pistols were displayed with a modified rough - textured frame, grip checkering, and interchangeable backstraps of different sizes . "Gen4" is rollmarked on the slide next to the model number to identify the fourth - generation pistols . </P> <P> The basic grip size of the fourth - generation Glock pistols is slightly smaller compared to the previous design . A punch is provided to remove the standard trigger housing pin and replace it with the longer cross pin needed to mount the medium or large backstrap that will increase the trigger distance by 2 mm (0.079 in) or 4 mm (0.16 in). With the medium backstrap installed, the grip size is identical to the third - generation pistols . The magazine release catches are enlarged and reversible for left - handed use . To use the exchangeable magazine release feature, fourth - generation Glock magazines have a notch cut on both sides of the magazine body . Earlier versions of the magazines will not lock into the Gen4 pistols if the user has moved the magazine release button to be operated by a left - handed user . Gen4 magazines will work in older models . </P>

When did the glock 17 gen 4 come out