How to make a pen gun

Under federal law, pen guns, with the exemption of the Stinger pen gun, are NFA-regulated firearms, classified “as any other weapon” (26 USC 5845(e)). This means that they are severely restricted weapons, but not illegal. … For example, a nonlicensee does not have to register this type of gun or pay a $5 stamp tax.

In the United States, pen guns that can fire bullet or shot cartridges and do not require a reconfiguration to fire (e.g., folding to the shape of a pistol) are federally regulated as an Any Other Weapon (Title II). … According to the FBI, pen guns were widely used for self-defense in the 20th century.

(d) No minor shall purchase, possess, or use tear gas or any tear gas weapon. (e) (1) No person shall purchase, possess, or use any tear gas weapon that expels a projectile, or that expels the tear gas by any method other than an aerosol spray, or that contains more than 2.5 ounces net weight of aerosol spray.

Modern ammunition is not dangerous on its own unless it is severely mishandled. Rounds are designed not to go off accidentally. They are made to only fire if they are struck in a particular manner. However, there are always exceptions and in addition, a round can cook off if exposed to fire.