I've had a double squib before. I had picked up an old Colt Police Positive Special, and being used to more modern "beefier" guns like Smith K-frames, that little gun just looked like it might not be up to firing full power loads (A gross underestimate on my part). I loaded up a batch of what I thought would be "light" 38 spl. rounds. The first squib sounded a little off, but with hearing protection on, I didn't know just how differently it sounded. When I saw the flash escaping around the cylinder on the second shot, I stopped and sure enough, the barrel was blocked. Took it to my gunsmith after my attempts at clearing the barrel with a dowel rod and rubber mallet failed. That's when I found out that there were not one, but two bullets lodged in there. Amazingly, it did not bulge the barrel at all. Never tried loading "light" after that!