Help Empower Americans to Respond Act of 2021 or the HEAR Act This bill establishes a new criminal offense for the import, sale, manufacture, transfer, or possession of a firearm silencer or firearm muffler. The bill does not prohibit certain conduct with respect to a firearm silencer or firearm muffler, including the following: importation, sale, manufacture, transfer, or possession related to certain law enforcement efforts, or authorized tests or experiments; and importation, sale, transfer, or possession related to securing nuclear materials. In addition, the bill requires the Department of Justice to establish and implement a buy-back program to purchase firearm silencers and firearm mufflers. States and local governments may use Edward Byrne Memorial Justice Assistance Grant Program funds to compensate individuals who surrender firearm silencers and firearm mufflers under this buy-back program.