He forgot that what he make is not exactly a gun that can be used by a kid or woman effectively, its a musket, and musket need a massed strength of everyone to be useful and shot in a volley, not to mention it takes ages to load and can't hit further than 100 meter or so accurately (except if mc knows about rifling)
I doubt he knows the tech of an actual bolt action rifle or bullet, not to mention the lack of precision tools to make it and the fact that he need PLENTY of bullet to make it useful