US SB2191

Requires federal firearms license to deal in ammunition and mandates background checks through the national instant criminal background check system (NICS) before licensed dealers can transfer ammunition to non-licensees

Prohibits bulk ammunition sales, limiting purchases to 100 rounds of .50 caliber ammunition or 1,000 rounds of other calibers within any 5-day period, with buyers required to provide written certification of compliance

Extends existing straw purchase prohibitions to cover ammunition and requires dealers to maintain ammunition transaction records for at least 2 years and transmit purchase forms to the Attorney General within 30 days

Establishes graduated penalties for dealer violations: $50,000-$250,000 fine for first offense, 60-day sales prohibition for second offense, and license revocation for third offense; buyer violations carry fines up to $50,000 and up to 5 years imprisonment

Authorizes up to $150 million for NICS system upgrades and requires annual ATF reports on ammunition sale violations, with provisions taking effect 120 days after enactment