Aw man m-80s sure are fun. Accidently stumbled upon one a few years back when a co-worker gave me a big ole box of commercial fireworks to take home for the Fourth. It was filled with all sorts of Class C stuff like bottle rockets, fountains, a few roman candles, and this menacing looking thing that was about the size of a large pill bottle, bright red, ends sealed with hot glue with a nice fat waterproof green fuze stickin out. I knew it was one of the fabled "illegal m-80s"
Took it down to the beach and tossed it into the ocean (lit of course) the blast was incredible, it sent a plume of water out of the ocean god only knows how high. The concussion could be heard echoing all the way down the beach. That thing easily could have taken off an entire arm. I dont know if it was an actual "m-80" but it certainly was made in someone's basement and was beyond powerful. Something tells me it was bigger than an M80, it was about 4 inches long with a diameter that was about the same as a silver dollar or so, when you shook it you could hear that it was maybe 2/3 filled with flash powder.