There is no Federal registration requirement for most conventional sporting firearms. Only those firearms subject to the National Firearms Act (NFA) (e.g., machineguns, short-barrel firearms, silencers, destructive devices, any other weapons) must be registered with ATF.
Please note that firearms registration may be required by State or local law. Any person considering acquiring a firearm should contact his or her State Attorney General’s Office to inquire about the laws and possible State or local restrictions. Firearms owners are encouraged to maintain personal records of their firearms to aid in recovery or investigation by State or local law enforcement agencies in the event a privately-owned firearm is stolen or lost. ATF recommends utilizing ATF Form 3312.8, Personal Firearms Record.