Glock handguns, especially the 9mm models, have had some very public reliability issues recently. Generation 3 and 4 Glock 17s and 19s that were made starting in 2009 have exhibited extraction issues that have been attributed to changes in the extractors. These new extractors may or may not be the issue but several people are reporting that Lone Wolf Distributing’s (LWD) Glock Extractors have cured their reliability woes.
It appears that the new potentially problematic extractor first showed up in the Gen4 Glocks and found its way into the Gen3 Glocks as early as 2009. The LWD extractor is based on the earlier Gen3 extractors with the loaded chamber indicator which proved to be a very capable and reliable extractor.
If you have a 2009 or later Gen3 or Gen4 Glock that is experiencing reliability issues, you might want to look into the LWD extractors as a potential fix. You can find the extractors on the LWD website.