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Fourth generation models
At the 2010 SHOT Show, Glock presented the "fourth generation" design, with updates centered on ergonomics and the recoil spring assembly. The fourth generation models do not have total parts modularity with its predecessors, meaning not all parts can be mixed and matched with previous Glock generations. The initial two fourth generation models announced were the full-size Glock 17 and Glock 22, chambered for the 9×19mm Parabellum and .40 S&W cartridges, respectively. The pistols were displayed with a modified rough texture 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.
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 for the longer cross pin needed to mount the medium or large backstrap. With the medium backstrap installed, the grip size is comparable to the third generation pistols. The magazine release catches are enlarged and reversible for left-handed use. To utilize the swappable magazine release feature, fourth generation Glock magazines have two notches cut on both sides of the magazine body.
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 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, in order to accommodate the dual recoil spring assembly. The trigger mechanism housing has also been modified to fit into the smaller sized grip space.[21][22][23][24][25]
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.[26] In late 2010 Glock continued the introduction of fourth generation models with the Glock 26 and Glock 27 "subcompact" variants.
In January 2013 more fourth generation Glock pistols are expected to be introduced commercially during the annual SHOT Show including the Glock 20 Gen4 along with other fourth generation Glock models.
2011 recoil spring assembly exchange program
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 “in order to ensure our products perform up to GLOCK’s stringent standards,” according the company.[27]
Comparison of "third" (left) and "fourth" generation (right) Glock 19 grip frames