Editing Firearm (section)

===United States===
In the [[United States]], under 26 USC § 5845 (a), the term "firearm" means

{{blockquote| {{plainlist|
* (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; 
* (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;
* (5) any other weapon, as defined in subsection (e); 
* (6) a machinegun; 
* (7) any silencer (as defined in section 921 of title 18, United States Code); <br /> The term "firearm" shall not include an antique firearm or any device (other than a machinegun or destructive device) which, although designed as a  weapon, the Secretary finds by reason of the date of its manufacture, value, design, and other characteristics is primarily a collector's item and is not likely to be used as a weapon.}}}}

This is the ATF definition of a [[Title II weapons|title II]] "NFA firearm", as defined by the [[National Firearms Act]], and not the definition of a title I firearm, which includes firearms not restricted by the NFA. ATF forms dealing with Title II weapons all state the above-mentioned information, however, the above information is only applicable for the purposes of those forms. For practical purposes, a firearm, in the U.S., is defined as the part of a weapon- designed to use expanded gas caused by the combustion of explosive material, to propel a projectile- which houses the fire control group (trigger & sear).

According to the U.S. [[Bureau of Alcohol, Tobacco, Firearms and Explosives]], if gas pressurization is achieved through ''mechanical'' [[gas compression]] rather than through chemical propellant combustion, then the device is technically an [[air gun]], not a firearm.<ref name=atfairgun>[http://www.atf.gov/firearms/faq/firearms-technology.html#air-gun-regulation US Federal Govt] {{Webarchive|url=https://web.archive.org/web/20150503044932/https://www.atf.gov/firearms/faq/firearms-technology.html#air-gun-regulation |date=2015-05-03 }} does not consider an air gun to be a firearm and does not regulate airguns as firearms</ref>