Just had a very close call with my ATP1 pistol, but this can happen with just about any PCP. Was having fun shooting lizards off my trees with a green laser sight. The lizards actually chase the green dot, thinking it's something to eat. Loads of fun. Shot down to empty on air, last shot chambered, but only got a small hiss when I fired, so I naturally knew the tank was down. Sure enough the gauge showed "0". Plugged in my fill probe, with the butt of the pistol resting on the floor, and barrel pointing up, so I could see the gauge. (My air tank is on a bottom shelf) slowly opened the valve on my tank, and heard a small hiss coming out the end of the barrel. OK, I know that sound, the tank is empty, and the valve in the pistol is not tightly closed, as no air to help seat it. So as in the past, it sometimes takes a blast of air to seat the valve. So, I gave the valve on my air tank, a quick twist open, and guess what? It fired the chambered pellet right past my head into the ceiling !!!!! Guy's, PLEASE be careful. It took me a few minutes to realize what had happened, and I realized it's not so hard to do, if not thinking, or in a hurry.