the other thing is the stock holds the lock and the barrel there is no mechanical connection lock to barrel , the barrel uses a wedge to hold it to the stock

if the stock rotted away the barrel could have separated , it may not be too far away or it may have found another use

Great find! It’s not uncommon to find just the lock as the natives used them to start fires (previously noted) after other parts of the gun failed. Most of the barrels you find are cut and not full length. Some of them are split or repurposed into hide scrapers etc. almost all of the locks have maker and a year stamped on them and occasionally you will find the serpent side plate that was affixed to the stock. You have a great piece of Minnesota fur trade history, good job!