Citation #1: State of Residence27 CFR §478.11 Meaning of terms.
State of residence. The State in which an individual resides. An individual resides in a State if he or she is present in a State with the intention of making a home in that State. If an individual is on active duty as a member of the Armed Forces, the individual's State of residence is the State in which his or her permanent duty station is located, as stated in 18 U.S.C. 921(b). The following are examples that illustrate this definition:
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Example 2. A maintains a home in State X and a home in State Y. A resides in State X except for weekends or the summer months of the year and in State Y for the weekends or the summer months of the year. During the time that A actually resides in State X, A is a resident of State X, and during the time that A actually resides in State Y, A is a resident of State Y.
http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&rgn=div8&view=text&node=27:3.0.1.2.3.2.1.1&idno=27Citation #2: Identification DocumentATF Rul. 2010-6
To ensure compliance with this residency requirement, section 922(t) of the GCA requires licensees to examine a valid "identification document" (as defined in 18 U.S.C. 1028(d) and 27 CFR 478.11) of a firearm transferee. This document must contain the residence address of the transferee so that the licensee may verify the identity of the transferee and discern whether the transferee has the intention of making a home in a particular State. Licensees transferring a firearm to a person not licensed under the GCA are required, pursuant to 27 CFR 478.124, to record the firearm transaction on an ATF Form 4473, which requires, among other things the transferee's residence address, including the transferee's State of residence as it appears on the valid identification document.
The term, "identification document" is defined by 18 U.S.C. 1028(d)(3) as "a document made or issued by or under the authority of the United States Government, a State, political subdivision of a Slots... which, when completed with information concerning a particular individual, is of a type intended or commonly accepted for the purpose of identification of individuals" The regulations, 27 CFR 478.11, define the term "identification document" as la] document containing the name, residence address date of birth, and photograph of the holder and which was made or issued by or under the authority of the United States Government, a State, political subdivision of a State. . .which, when completed with information concerning a particular individual, is of a type intended or commonly accepted for the purpose of identification of individuals." Identification documents include, but are not limited to, a driver's license, voter registration, tax record, or vehicle registration. As explained in ATF Ruling 2001-5 (ATFQB 2001-4, 37), a combination of valid government documents may be used to satisfy the GCA's State residency requirement.
ATF has previously addressed the eligibility of individuals to acquire firearms who maintain residences in more than one State. Federal regulations at 27 CFR 478.11 (definition of State of Residence), Example 2, clarify that a U.S. citizen with homes in two States may, during the period of time the person actually resides in a particular State, purchase a firearm in that State. See also ATF Publication 5300.4 (2005), Question and Answer B12, page 179. Similarly, in ATF Ruling 80-21 (ATFB 1980-4, 25), ATF held that, during the time college students actually reside in a college dormitory or at an off-campus location, they are considered residents of the State where the on-campus or off-campus housing is located.
http://www.atf.gov/files/regulations-rulings/rulings/atf-rulings/atf-ruling-2010-6.pdfCitation #3: Alternate forms of IdentificationATF From 4473
Question 20.b. Alternate Documentation: Licensees may accept a combination of valid government-issued documents to satisfy the identification document requirements of the law. The required valid government-issued photo identification document bearing the name, photograph, and date of birth of transferee may be supplemented by another valid, government-issued document showing the transferee's residence address. This alternate documentation should be recorded in question 20.b., with issuing authority and type of identification presented. A combination of government-issued documents may be provided. For example, if a U.S. citizen has two States of residence and is trying to buy a handgun in State X, he may provide a driver's license (showing his name, date of birth, and photograph) issued by State Y and another government-issued document (such as a tax document) from State X showing his residence address.
http://www.atf.gov/files/forms/download/atf-f-4473-1.pdf