<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> <P> In September 2011, Glock announced a recoil spring exchange program in which the manufacturer voluntarily offers to exchange the recoil spring assemblies of its fourth - generation pistols (with the exception of the "subcompact" Glock 26 and Glock 27 models) sold before 22 July 2011 at no cost "to ensure our products perform up to GLOCK's stringent standards", according to the company . </P>

When did the glock 19 gen 3 come out