Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 131, § 66

A person shall not, except during the prescribed open season when deer may be hunted lawfully with a shotgun, have in his possession a shotgun shell loaded with a rifled slug, single ball, buckshot of any size, BB shot or air rifle shot in any place where birds or mammals might be found, except on a skeet, trap or target range between sunrise and sunset; provided, however, that the director shall promulgate rules and regulations prescribing the type and size of such BB shot.