The Buy American Act was passed by U.S. Congress in 1933.
The purpose of the Buy American Act is to provide preferential treatment for domestic sources of unmanufactured articles, manufactured goods, and construction material for public use unless a specific exemption applies.
The act requires the federal government to purchase domestic supplies for use in the United States, if:
The supply contract exceeds the micro-purchase threshold; or

The supply portion of a contract for services that involves the furnishing of supplies exceeds the micro-purchase threshold. In determining what are domestic goods, the place of mining, production, or manufacture is controlling.

10 U.S.C. 2473 - PROCUREMENTS FROM THE SMALL ARMS PRODUCTION INDUSTRIAL BASE


(a) Requirement To Limit Procurements To Certain Sources.—


In order to preserve the small arms production industrial base, the Secretary of Defense shall require that any procurement of property or services described in subsection (b) for the Department of Defense be made only from a firm in the small arms production industrial base, unless the Secretary determines, with regard to a particular procurement, that such requirement is not necessary to preserve the small arms production industrial base.


(b) Covered Property and Services.—


Subject to subsection (d), subsection (a) applies to the following:


(1) Critical repair parts for small arms, consisting only of barrels, receivers, and bolts.
(2) Modifications of such parts to improve small arms used by the armed forces.
(c) Small Arms Production Industrial Base.—
In this section, the term small arms production industrial base means the firms comprising the small arms production industrial base, as described in the plan entitled Preservation of Critical Elements of the Small Arms Industrial Base, dated January 8, 1994, that was prepared by an independent assessment panel of the Army Science Board.
(d) Applicability.—


This section applies only to procurements of covered property and services involving the following small arms:


(1) M16 series rifle.
(2) MK19 grenade machine gun.
(3) M4 series carbine.
(4) M240 series machine gun.
(5) M249 squad automatic weapon.
(e) Submission of Certified Cost or Pricing Data.—


If a procurement under subsection (a) is a procurement of a commercial item, the Secretary may, notwithstanding section 2306a (b)(1)(B) of this title, require the submission of certified cost or pricing data under section 2306a (a) of this title.