Superposed load
A superposed load or stacked charge or superimposed load is a method used by various muzzle-loading firearms, from matchlocks to caplocks, as well as newer Metal Storm weapons, to fire multiple shots from a single barrel without reloading. In a sense, superposed load guns were the first automatic firearms, as they fired multiple shots per pull of the trigger. Design. Superposed loads are loads that are placed in the barrel, one on top of the other, so that there is an alternating sequence of (from the breach end) powder, ball, powder, ball, etc., for the desired number  of charges. Each charge is accompanied by a corresponding touch hole that allows ignition of that charge. In the simplest case, the matchlock, each touch hole is individually primed and ignited with the match, front to rear. Each ball behind the first acts as a seal, to prevent ignition of the next charge. Flintlocks using superposed charges often involved a sliding lock, that slid along the barrel and locked in place at each successive touch hole. The lock would be primed, cocked, and fired at each touch hole to discharge successive charges. Some caplock designs used multiple hammers, each impacting  a nipple leading to a different charge, allowing true rapid fire. History. Designs using superposed loads have appeared periodically throughout firearms history, though they have met with only limited success. They have always been plagued with issues of sequential charges firing together, which can result in a burst barrel and injury to the user.