Keep Americans Safe Act This bill establishes a new criminal offense for the import, sale, manufacture, transfer, or possession of a large capacity ammunition feeding device (LCAFD). The bill does not prohibit certain conduct with respect to an LCAFD, including the following: importation, sale, manufacture, transfer, or possession related to certain law enforcement efforts, or authorized tests or experiments; importation, sale, transfer, or possession related to securing nuclear materials; and possession by a retired law enforcement officer. The bill permits continued possession of, but prohibits sale or transfer of, a grandfathered LCAFD. Newly manufactured LCAFDs must display serial number identification and the date of manufacture. Additionally, the bill allows a state or local government to use Edward Byrne Memorial Justice Assistance Grant Program funds to compensate individuals who surrender an LCAFD under a buy-back program.