I found this pretty interesting when I was shopping for a gun...
SPRINGFIELD ARMORY
In short, they did a crazy torture test on the XD that included freezing the gun, covering it in dirt, mud, and degreasing it, and firing off rounds in between all of that. After they did that, they fired off another 1,700 rounds. 20,000 rounds in total, and not a single malfunction. I thought that was pretty damn impressive.