Default Proceed Sale Transparency Act This bill establishes new requirements in the case of a firearm transfer by a federally licensed dealer, manufacturer, or importer to an unlicensed person prior to the completion of a background check. Current law permits these transactions—default-proceed transactions—if a submitted background check remains incomplete after three business days. With respect to a default-proceed transaction, the bill requires a federally licensed dealer, manufacturer, or importer to report the transfer to the Federal Bureau of Investigation (FBI) within 24 hours; requires the instant criminal background check system (NICS) to prioritize completing the background check related to the transfer; and requires the NICS to retain records related to a proposed or completed firearm transfer until the background check is complete. Finally, the bill requires the FBI to report publicly on data related to default-proceed transactions. Further, it requires the Bureau of Alcohol, Tobacco, Firearms and Explosives to report publicly on data related to the firearms transferred in default-proceed transactions.