"the pepperbox muzzle of a flechette pistol emerged from her hands."
Public Domainpepperboxillustration - Credit: atrilogy

Molly Millions’ flechette pistol is based on the first repeating firearms, called pepper-box revolvers. 

Pepper-box revolvers, or needle guns, have multiple barrels that revolve about a central axis. They take a long time to load but are quick to fire. Molly's pepperbox gun fires flechettes, or darts.