>makeshift weapons
>a firearm
Come on now m9, the only kind of weapon more difficult to make from scratch than a gun is a railgun.
Your realistic options:
>mace
>flail
>spear
>sword
Excluding knives because anything moderately sharp would pass for a knife. Bows are difficult to make and making arrows is even more difficult. A reasonably thick (¼-⅜") plate metal can be made into a very decent sword using little more than any grinding tool. If you have a cache of straight rods, a winch and a leaf spring at your disposal, you can attempt making a crossbow; good crossbow draw force starts at 250 lbs.