I saw this happen
My brother had a well worn SIG226 (probably well over 20k rounds) and at the range he hit the decocker and BAM! We both lookat at each other like ***? Also, I always use the slide lock to indicate to me and everyone else that the weapon is clear ever since I saw a rookie who had only shot 1911's have a AD when he put his Glock down on the range table and it "Just went off". What most likely happened was that he had gotten careless about putting his finger on the trigger because his 1911 was "on safe". He had quite a nasty cut and a big old welt on his hand, but the round at least went down range.
Truth is, you can follow the 4 rules and still have an AD. It happened to me at the range once. I was shooting my old CZ52. I inserted a loaded mag and racked the slide. Checked to make sure the safety was off and started putting holes in the target. After my 3rd shot, the range instructor told everyone to finish out their current mag and put the weapons down for a cease fire. Alright, no problem. Finger out of trigger guard, pistol pointed downrange, pushed the decocker to "safely" drop the hammer before taking the mag out. *click* <2 seconds> *BLAM*. Not sure why, but the primer ignited 2 seconds after the decocker engauged. The stray round impacted the dirt embankment downrange.
My brother had a well worn SIG226 (probably well over 20k rounds) and at the range he hit the decocker and BAM! We both lookat at each other like ***? Also, I always use the slide lock to indicate to me and everyone else that the weapon is clear ever since I saw a rookie who had only shot 1911's have a AD when he put his Glock down on the range table and it "Just went off". What most likely happened was that he had gotten careless about putting his finger on the trigger because his 1911 was "on safe". He had quite a nasty cut and a big old welt on his hand, but the round at least went down range.