Gun law in the United States protects individuals who sell parts of or accessories to firearms, consumers who buy them and any third parties engaged in the transactions. However, laws also govern the sale of gun parts as well, rendering it unlawful to sell even parts of guns or gun accessories to individuals who do not possess the proper licenses. If these laws are not followed, buyers and sellers can be prosecuted.
The sale of gun parts is highly regulated by federal and state governments. Most states have laws that make it illegal to sell any gun parts, working or nonworking, to an individual who does not possess a valid gun permit. In some states, these laws are based on the legality of the weapon in question. For example, federal law requires an individual who wishes to purchase a pistol to fill out federal form 4473, but the approval of individuals who fill out this form does not guarantee that they will be able to purchase parts of a gun other than a pistol (i.e., machine guns, shotguns and rifles in part or in whole), nor many components of other unapproved or illegal weapons.
Gun accessories sales are not as heavily regulated in the United States as are sales of gun parts. Whereas parts and pieces of guns can function when combined with other pieces or be modified to work on their own, most gun accessories cannot. A notable exception is when the gun accessories being sold would render use of the gun illegal. Most silencers or suppressors fall into this category. Because silencers are unlawful in most states and on most weapons, they are not often eligible for sale, even to individuals who qualify.
Gun laws vary by state and even by locality, so sales of gun parts and accessories are entirely different from one area to the next. In certain areas, sale of parts by certain makers and manufacturers is prohibited. The U.S. Attorney General lists a roster of handguns certified for sale. If a gun does not appear on the roster, oftentimes the sale of accessories (even lawful ones) and parts is illegal. The best way to avoid confusion is to contact the attorney general's office for your state and check to find out what firearms pieces and accessories can and cannot be sold in your state.