<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> <P> Mechanically, fourth - generation Glock pistols are fitted with a dual recoil spring assembly to help reduce perceived recoil and increase service life expectancy . Earlier subcompact Glock models such as the Glock 26 and Glock 30 have already used a dual recoil spring assembly which was carried over to the fourth - generation versions of those models . The slide and barrel shelf have been resized, and the front portion of the polymer frame has been widened and internally enlarged, to accommodate the dual recoil spring assembly . The trigger mechanism housing has also been modified to fit into the smaller - sized grip space . </P> <P> The introduction of fourth - generation Glock pistols continued in July 2010 when the Glock 19 and Glock 23, the reduced size "compact" versions of the Glock 17 and Glock 22, became available for retail . In late 2010, Glock continued the introduction of fourth - generation models with the Glock 26 and Glock 27 "subcompact" variants . </P> <P> In January 2013, more fourth - generation Glock pistols were introduced commercially during the annual SHOT Show, including the Glock 20 Generation 4 along with other fourth - generation Glock models . </P>

When was the glock 19 gen 4 released