In the early days of firearms manufacturing, individual craftsmen made individual components one at a time. One craftsman made the "lock '' which would have been a "match lock '', "wheel lock '', "flint lock '' etc. The next craftsman made the barrel, and the last craftsman, who was a woodworker made the stock. At some point, a craftsman or a merchant started advertising "Lock Stock and Barrel '' meaning that you could get your entire gun at one location and did not have to go from craftsman to craftsman to get it finished.
where does lock stock and barrel come from
you could get your entire gun at one location and did not have to go from craftsman to craftsman to get it finished