In the early 1950s a buddy and I built a cannon from water pipe with the carriage made of 2X4s. We made our black powder from sulfer, saltprete, and charcoal (amounts I don't recall). we test fired it in the alley behind our houses. We used marbles for our projectiles. We fired our first shot. A very loud blast, a large cloud of smoke, and a sound of breaking glass down the alley. We rapidly torn the "Cannon" apart and relocated ourselves to another area (ie-in our houses reading a book). A neighbor down the alley was enquiring about an exploson and did anyone witness his picture window breaking ?