I have a Glock 21 model that is about 12 years old. I purchased the weapon 5 years ago and little usage on the pistol. Today in the middle of qualifying for my CHL(Texas) renewal on the range course when instructed to load my magazine, I slapped it in and to my surprise the slide released forward without me pulling on it, as soon as the magazine was put in and seated the slide released on its own. Fortunately the instructor say what happened and did not ding me on it, but he said I might want to get that checked out. Anyone out there have this happen before and if so any idea what is the culprit? As stated I purchased it with what seemed little usage on it, and since I have owned it have probably put around 1,500 rounds through it.