Hello jackg:
I'd like to try to answer this if I may.
I'm a career cop. I bought my first Glock, a G17 9mm, in 1991. My fellow officers thought that I was crazy since it wasn't a S&W .357 Magnum revolver. In the time that has followed, those same skeptical officers are now carrying Glocks in .40 on duty. To put it simply, Glocks absolutely WORK as often as you can reasonably expect something made by man to work and lemons are rare. In the past 20 years, I've owned all manner of Glock pistols, and I've NEVER had a single one that was unreliable out of the box. My experiences echoes that of my fellow officers and civilian concealed carry permit holders whom I've trained over the last decade.
Empirical evidence?
*During early 2009, one of our female police recruits bought a used G22 .40 from "Jo-Jo the Gun Plumber." The plunger was in BACKWARDS, as was its spring, and the bearing was competely MISSING. This wasn't noticed until AFTER firearms week, when she had already shot 1500 rounds...with NO MALFUNCTIONS.
*Approximately 2 years ago, one of our police recruits had a G22 with a visiblity chipped extractor near where it grasps the spent casing for ejection after firing. We did not have an extra part, so he continued to use G22. It never failed, even after 1500 rounds in 5 days.
*A fellow police academy instructor recently bought a new G19 9mm. While at the range after a heavy rain, he locked the slide back on his empty G19 and placed it on a plastic barrel while loading magazines. It fell muzzle-down into the mud and buried up past the dust cover to the trigger guard. He picked it up, ensured that the barrel was clear, and fired back-to-back 2 qualification courses (100 rounds)...with no malfunctions.
*In the early 90s, a friend of mine had a Generation 1 G17 9mm and a coffee-can full of inferior quality reloads of all configurations and bullet weights. They were in terrible shape, covered by corrosion, and oftentimes, green. His Glock 17 fed them all...every single one of them, with no visible degredation in accuracy.
I'm not going to say Glocks are perfect. They have their drawbacks, but I will say that in 2 decades on the range, I can attest to you that STATISTICALLY and MECHANICALLY, they are the most reliable sidearms I've ever seen.
To this day, the weapon I choose to defend myself, my family and my home, is a Glock 19, and I sleep very well.
