My brother recently acquired a Colt Commander. He had put a Federal hollowpoint in the chamber and lowered the hammer (condition #2). He was holstering the pistol with the hammer down. This was a holster with a thumb break. As he attempted to adjust the pistol in order to snap the thumb break closed, the pistol discharged. The round traveled into his upper right butt cheek and out the bottom, about 6 inches below his butt cheek. The round didn't expand and fell to the floor under the weight of gravity alone. He is fine now but the AD [accidental discharge] perplexed us a lot until we figured that the hammer was resting on the firing pin, and the soft primer Federal hollowpoint round and the hard "snap" of the new holster hit the hammer hard enough to touch off a round. Fixing the issue is to simply not chamber a round, period.