The Stop Arming Cartels Act of 2024 prohibits the importation, sale, manufacture, transfer, and possession of .50 caliber rifles, with limited exceptions for government agencies and firearms lawfully owned before the bill's enactment. The legislation creates a one-year window for current owners of such rifles to register them with federal authorities at no cost, and grandfathers in rifles legally possessed before the law takes effect. The bill also establishes new federal prohibitions on firearm transfers to foreign narcotics traffickers designated by the President or Treasury Department, making it easier to prosecute those who knowingly sell weapons to such individuals. Additionally, it requires firearms dealers to report multiple rifle sales in the same manner they currently report multiple handgun sales. The bill does not authorize new federal funding but relies on existing agency resources and the National Firearms Registration system to implement these provisions.