I finally came up with a pair of weapons for Jack-0!

Shortspear: A decent close-range weapon with throwing capabilities. It can deflect both solid and energy projectiles.

Piercer: a common modified ranged weapon that can utilize any metal as ammo. Since JACK-0 can crush many metals with his hands alone, all he has to do is put it in the chamber and the metal will be shoot out rapidly as sharpened, heated projectiles.