The Department of Justice (“Department”) is amending Bureau of Alcohol, Tobacco, Firearms, and Explosives (“ATF”) regulations to remove and replace the regulatory definitions of “firearm frame or receiver” and “frame or receiver” because the current regulations fail to capture the full meaning of those terms. The Department is also amending ATF's definitions of “firearm” and “gunsmith” to clarify the meaning of those terms, and to provide definitions of terms such as “complete weapon,” “complete muffler or silencer device,” “multi-piece frame or receiver,” “privately made firearm,” and “readily” for purposes of clarity given advancements in firearms technology. Further, the Department is amending ATF's regulations on marking and recordkeeping that are necessary to implement these new or amended definitions.