Technically it is illegal to sell ammo in the state of Massachusetts without the proper license.
ma general law chapter 146 section 122b is listed below however I have never heard of anyone being arrested for selling a box of 100 rounds to a fellow licensed to carry individual.
Section 122B. No person shall sell ammunition in the commonwealth unless duly licensed. The chief of police or the board or officer having control of the police in a city or town, or persons authorized by them, may, after an investigation into the criminal history of the applicant to determine eligibility to be licensed under this section, grant a license to any person, except an alien, a minor, a person who has been adjudicated a youthful offender, as defined in section fifty-two of chapter one hundred and nineteen, including those who have not received an adult sentence or a person who has been convicted of a felony in any state or federal jurisdiction, or of the unlawful use, possession or sale of narcotic or harmful drugs, to sell ammunition. Every license shall specify the street and number, if any, of the building where the business is to be carried on. The licensing authority to whom such application is made shall cause one copy of the application to be forwarded to the commissioner of the department of criminal justice information services, who shall within a reasonable time thereafter advise such authority in writing of any criminal record disqualifying the applicant. The fee for an application for a license to sell ammunition shall be $100, which shall be payable to the licensing authority and shall not be prorated or refunded in case of revocation or denial. The licensing authority shall retain $25 of the fee; $50 of the fee shall be deposited into the general fund of the commonwealth; and $25 of the fee shall be deposited in the Firearms Fingerprint Identity Verification Trust Fund. The licensing authority to whom such application is made shall cause one copy of any approved application to be forwarded to the commissioner of the department of criminal justice information services.
Any lawfully incorporated sporting or shooting club shall, upon application, be licensed to sell or supply ammunition for regulated shooting on their premises, as for skeet, target or trap shooting; provided, however, that such club license shall, in behalf of said club, be issued to and exercised by an officer or duly authorized member of the club who himself possesses a firearm identification card or a license to carry a firearm and who would not be disqualified to receive a license to sell ammunition in his own right. The licensing authority may revoke or suspend a license to sell ammunition for violation of any provision of this chapter.
The secretary of the executive office of public safety may establish such rules and regulations as he may deem necessary to carry out the provisions of this section.
Any person refused a license under this section or once issued a license under this section has had said license suspended or revoked may obtain a judicial review of such refusal, suspension or revocation by filing within thirty days of such refusal, suspension or revocation a petition for review thereof in the district court having jurisdiction in the city or town in which the applicant filed for such license, and a justice of said court, after a hearing, may direct that a license be issued the applicant if satisfied there was no reasonable ground for refusing such license and that the applicant was not prohibited by law from holding the same.
Whoever not being licensed, as hereinbefore provided, sells ammunition within the commonwealth shall be punished by a fine of not less than five hundred nor more than one thousand dollars or by imprisonment for not less than six months nor more than two years.
