Title II weapons
Title II weapons, or NFA firearms, are certain firearms, explosive munitions, and other devices which are legally regulated in the United States by the National Firearms Act (NFA). Any violation of the NFA is a felony punishable by up to 10 years in prison. Per the Summary of Gun Control Act of 1968:
Title II of the Gun Control Act of 1968 is a revision of the National Firearms Act of 1934, and pertains to machine guns, short or "sawed-off" shotguns and rifles, and so-called "destructive devices" (including grenades, mortars, rocket launchers, large projectiles, and other heavy ordnance). Acquisition of these weapons is subject to prior approval of the Attorney General, and federal registration is required for possession. Generally, a $200 tax is imposed upon each transfer or making of any Title II weapon.
The Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), which enforces federal firearms law, refers to such weapons as "NFA firearms". In addition to machine guns, short-barreled rifles and shotguns, heavy weapons and explosive ordnance, NFA firearms include silencers and "any other weapon" (AOW), such as disguised or improvised firearms.
Explosive devices such as bombs or grenades are regulated as NFA firearms (destructive devices). Explosive materials are not considered NFA firearms; they are regulated under the Organized Crime Control Act.
Category definitions 
Machine Guns 
A machine gun is defined as a weapon which shoots "automatically more than one shot, without manual reloading, by a single function of the trigger." Additionally, the frame or receiver of a machine gun, and any combination of parts intended to make a machine gun is legally equivalent to a complete machine gun.
For example, per the ATF, "A Glock conversion switch is a part designed and intended for use in converting a semiautomatic Glock pistol into a machinegun; therefore, it is a “machinegun” as defined in 26 U.S.C. 5845(b)."
Short-Barreled Shotguns 
A Short-Barreled Shotgun (SBS) is defined as:
- (1) a shotgun having a barrel or barrels of less than 18 inches in length;
- (2) a weapon made from a shotgun if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 18 inches in length;
It must be intended to be fired from the shoulder and fire one shell of ball shot or one projectile at a time.
Short-Barreled Rifles 
A Short-Barreled Rifle (SBR) is defined as:
- (3) a rifle having a barrel or barrels of less than 16 inches in length;
- (4) a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length;
A rifle is a firearm designed to be fired from the shoulder and fire one bullet at a time through a rifled barrel. An SBR may or may not retain a shoulder stock after modification.
ATF regards pistols with shoulder stocks as redesigned to be fired from the shoulder. Modern pistols with shoulder stocks and with barrels less than 16 inches (or overall length under 26 inches) are NFA short barrelled rifles. ATF has removed certain stocked handguns (e.g., original Mauser C96 and Luger) from the NFA as collector's items (Curios or Relics List); ATF treats them as pistols under the GCA. Queries on the Curio or Relic status of an NFA firearm may be directed to the ATF FTB.
Destructive Devices 
There are two categories of Destructive Devices (DDs):
- Explosive ordnance
- Any explosive, incendiary, or poison gas, including bombs, grenades, rockets, missiles, mines and similar devices (e.g. grenade launchers, rocket launchers). Parts intended for making such a device are also DDs. Small rockets, with less than 4 ounces of propellant, are exempt.
- Large bore firearms
- Any projectile weapon with a bore diameter greater than 1⁄2 inch (50 caliber), except for shotguns "generally recognized as particularly suitable for sporting purposes".
Most commercial shotguns have a bore diameter greater than 1⁄2 inch, but are exempt due to their "sporting purpose"; however, both the Street Sweeper and USAS-12 shotguns (designed for military or police use) were reclassified as DDs when the ATF determined they were combat shotguns not "generally recognized as particularly suitable for sporting purposes".
Devices which are not intended or not likely to be used as a weapon are also exempt. Examples of non-weapon large bore firearms include:
- Line-throwing devices for marine rescue, such as lyle guns and rockets for breeches buoys.
- Civilian flare guns, which fire 37 mm flare caliber (1.46 inch) non-weapon rounds.
Examples of non-weapon explosive ordnance include:
Flare launchers are normally exempt as they are signalling devices, not weapons; however, possession of a flare launcher and anti-personnel ammunition for it puts it in the DD category as it is then considered to be a weapon.
A silencer (muffler or suppressor) is defined as "any device for silencing, muffling, or diminishing the report of a portable firearm, including any combination of parts ... intended for use in assembling or fabricating a firearm silencer."
Any Other Weapon 
"Any other weapon" is a "catch-all" category. An AOW as defined as "any weapon or device capable of being concealed on the person from which a shot can be discharged through the energy of an explosive," other than a handgun with a rifled barrel. This umbrella definition includes many improvised firearms ("zip guns") and disguised firearms. Examples include wallet guns, cane guns, knife guns and pen guns.
AOW is a complex and often misunderstood category of NFA firearms. Less obvious examples of AOW devices include:
- Short-barreled (<18") shotguns manufactured without a shoulder stock
- They are smooth-bore handguns which fire shot shells, not shotguns, which must be designed to be fired from the shoulder.
- Pistols with a second vertical grip
- Many pistols feature a rail below the barrel, commonly used to mount a laser or flashlight. Attaching a vertical grip to this rail constitutes the manufacturing of an AOW firearm, as it is "no longer designed to be held and fired by the use of a single hand." It is therefore illegal to place an aftermarket foregrip on any pistol without first registering it as an AOW and paying the $200 "making tax". Failure to do so is a felony punishable by up to 10 years in prison.
And folding stock guns with barrels between 12 and 18 inches (e.g., the Marble Game Getter, an early 20th century sporting gun common before the NFA).
Antique firearms 
Antique firearms are excluded from the destructive devices category if they are "not likely to be used as a weapon."  They must have been manufactured before 1898 and may not use conventional ammunition.26 U.S.C. § 5845(g). "The term “antique firearm” means any firearm not designed or redesigned for using rim fire or conventional center fire ignition with fixed ammunition and manufactured in or before 1898 (including any matchlock, flintlock, percussion cap, or similar type of ignition system or replica thereof, whether actually manufactured before or after the year 1898) and also any firearm using fixed ammunition manufactured in or before 1898, for which ammunition is no longer manufactured in the United States and is not readily available in the ordinary channels of commercial trade." For example, muzzle loaded matchlock and flintlock muskets with bores larger than .50 inch are not NFA firearms.
Numerous federal restrictions are imposed on the ownership of NFA firearms, including required registration with the ATF, an extensive background check, and a $200 tax on each purchase, transfer or manufacture of an NFA firearm.
Silencers and machine guns are the most heavily regulated.
AOW weapons are less restricted. The transfer tax for an AOW is just $5.
State laws on NFA firearms 
A few states, such as New York and California, have provisions in their state laws that prohibit ownership of Title II weapons and devices. Most states allow legal ownership if the owner has complied with the federal registration and taxation requirements. A few states only allow possession of NFA firearms on the federal Curios and Relics list, again only if the owner has complied with federal requirements.
See also 
- : Chapter 53—Machine Guns, Destructive Devices, and Certain other Firearms
- : Definitions
- 26 U.S.C. § 5871. "Any person who violates or fails to comply with any provisions of this chapter shall, upon conviction, be fined not more than $10,000, or be imprisoned not more than ten years, or both."
- "Federal Firearms Laws". NRA-ILA. Retrieved 2011-03-28.
- See, e.g., "National Firearms Act (NFA)". www.atf.gov. ATF. Retrieved 2011-03-28.
- "ATF Explosives Industry Newsletter : June 2004", Federal Explosives Licensee (FEL) Newsletter (ATF), retrieved 2011-03-31, "The Federal law dealing with explosive[s] is the Organized Crime Control Act, or OCCA, Title 18 U.S.C. § 841 et seq."
- "National Firearms Act Definitions - Machinegun". www.atf.gov. ATF. Retrieved 2011-03-29. "For the purposes of the National Firearms Act the term Machinegun means:
- Any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot without manual reloading, by a single function of the trigger
- The frame or receiver of any such weapon
- Any part designed and intended solely and exclusively or combination of parts designed and intended for use in converting a weapon into a machinegun, or
- Any combination of parts from which a machinegun can be assembled if such parts are in the possession or under the control of a person."
- "Firearms Technology FAQ". www.atf.gov. ATF. Retrieved 2011-03-29.
- 26 U.S.C. § 5845(a)(1,2)
- 26 U.S.C. § 5845(d). "The term “shotgun” means a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of the explosive in a fixed shotgun shell to fire through a smooth bore either a number of projectiles (ball shot) or a single projectile for each pull of the trigger, and shall include any such weapon which may be readily restored to fire a fixed shotgun shell."
- 26 U.S.C. § 5845(a)(3,4)
- 26 U.S.C. § 5845(c). "The term “rifle” means a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of the explosive in a fixed cartridge to fire only a single projectile through a rifled bore for each single pull of the trigger, and shall include any such weapon which may be readily restored to fire a fixed cartridge."
- Firearms Curios or Relics List. ATF Publication 5300.11. Revised Dec 2007.
- ATF FAQ National Firearms Act, Q: Shoulder Stock Pistol.
- Bureau of Alcohol, Tobacco, Firearms and Explosives, Firearms Technology Branch, 244 Needy Road, Martinsburg, WV 25405.
- 26 U.S.C. § 5845(f)
- 18 U.S.C. § 921(a)(24). "The terms “firearm silencer” and “firearm muffler” mean any device for silencing, muffling, or diminishing the report of a portable firearm, including any combination of parts, designed or redesigned, and intended for use in assembling or fabricating a firearm silencer or firearm muffler, and any part intended only for use in such assembly or fabrication."
- "National Firearms Act Definitions - Any Other Weapon". www.atf.gov. ATF. Retrieved 2011-03-29. "For the purposes of the National Firearms Act, the term “Any Other Weapon” means:
- Any weapon or device capable of being concealed on the person from which a shot can be discharged through the energy of an explosive;
- A pistol or revolver having a barrel with a smooth bore designed or redesigned to fire a fixed shotgun shell;
- Weapons with combination shotgun and rifle barrels 12 inches or more, less than 18 inches in length, from which only a single discharge can be made from either barrel without manual reloading; and
- Any such weapon which may be readily restored to fire.
- "Firearms Technology FAQ". www.atf.gov. ATF. Retrieved 2011-03-29. "ATF has long held that by installing a vertical fore grip on a handgun, the handgun is no longer designed to be held and fired by the use of a single hand. Therefore, if individuals install a vertical fore grip on a handgun, they are “making” a firearm requiring registration with ATF’s NFA Branch. Making an unregistered “AOW” is punishable by a fine and 10 years’ imprisonment. Additionally, possession of an unregistered “AOW” is also punishable by fine and 10 years’ imprisonment."
- 26 U.S.C. § 5872(a). "Any firearm involved in any violation of the provisions of this chapter shall be subject to seizure and forfeiture."