This bill, titled the "Closing the Bump Stock Loophole Act of 2025," amends federal law to address devices and modifications that significantly increase the rate of fire of semiautomatic firearms. It establishes a definition for a semiautomatic firearm , clarifying it as a weapon that cycles automatically but requires a separate trigger pull for each shot, distinct from a machinegun. The legislation aims to prevent the circumvention of machinegun prohibitions through accessory devices or firearm alterations. Specifically, the bill makes it unlawful to import, sell, manufacture, transfer, receive, or possess any device primarily designed to materially increase a semiautomatic firearm's rate of fire or approximate a machinegun's action. This includes devices that eliminate the need for separate trigger movement for each shot, effectively banning mechanisms like bump stocks. Furthermore, it prohibits semiautomatic firearms that have been modified to achieve these rapid-fire capabilities, requiring that any lawfully owned, pre-existing modified semiautomatic firearms be registered under the National Firearms Act within 120 days of enactment.