Possessing a firearm intended to be fired from the shoulder with a rifled barrel less than 16 inches in length or possessing a non-rifled shoulder fired firearms with a smooth barrel of less than 18.5 inches. You must pay a $200 tax or risk prison before exercising your second amendment rights in this fashion.
The $5 tax is for Any Other Weapon, which has a considerably more convoluted definition, but one way to create an AOW is to put a plastic handle on the front of your pistol.