So, I recently made a terrible mistake, one that is extremely dangerous, and I want to make sure that nobody else does the same thing. I have a .22 conversion for my AR, and I was using it the other day. When I was done at the range for the day, I took it out and put the regular bolt carrier assembly back in. About a week later, I was at home and decided to put the conversion back in. I took out the regular bolt carrier. Obviously the chamber was clear, there was no bolt in it and I could see down the length of the barrel. I put the 22 conversion, pulled the trigger to ease the springs, and... BANG! I fired a shot through my mattress and into the base of my headboard. Apparently when I removed the conversion at the range, there was a round in it, and it hadn't occurred to me that the round is actually chambered inside the conversion, and that I could absolutely remove it with a round still chambered. This is by far the stupidest thing I've ever done, and I want to make sure that nobody else ever makes the same mistake.