27 CFR 478.125
g) Commercial records of firearms received. When a commercial record is held by a licensed dealer or licensed collector showing the acquisition of a firearm or firearm curio or relic, and such record contains all acquisition information required by the bound record prescribed by paragraphs (e) and (f) of this section, the licensed dealer or licensed collector acquiring such firearm or curio or relic, may, for a period not exceeding 7 days following the date of such acquisition, delay making the required entry into such bound record: Provided, That the commercial record is, until such time as the required entry into the bound record is made, (1) maintained by the licensed dealer or licensed collector separate from other commercial documents maintained by such licensee, and (2) readily available for inspection on the licensed premises: Provided further, That when disposition is made of a firearm or firearm curio or relic not entered in the bound record under the provisions of this paragraph, the licensed dealer or licensed collector making such disposition shall enter all required acquisition information regarding the firearm or firearm curio or relic in the bound record at the time such transfer or disposition is made.