Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 140, § 131L

(a) It shall be unlawful to store or keep any firearm in any place unless such firearm is secured in a locked container or equipped with a tamper-resistant mechanical lock or other safety device, properly engaged so as to render such firearm inoperable by any person other than the owner or other lawfully authorized user. It shall be unlawful to store or keep any stun gun in any place unless such firearm is secured in a locked container accessible only to the owner or other lawfully authorized user. For purposes of this section, such firearm shall not be deemed stored or kept if carried by or under the control of the owner or other lawfully authorized user.

(b) A violation of this section shall be punished, in the case of a that is not a large capacity firearm or machine gun, by a fine of not less than $1000 nor more than $7,500 or by imprisonment for not more than 1 1/2 years or by both such fine and imprisonment and, in the case of a large capacity or semiautomatic weapon or machine gun, by a fine of not less than $2,000 nor more than $15,000 or by imprisonment for not less than 1 1/2 years nor more than 12 years or by both such fine and imprisonment.

(c) A violation of this section shall be punished, in the case of a that is not a large capacity firearm or machine gun and the firearm was stored or kept in a place where a person younger than 18 years of age who does not possess a valid firearm identification card issued under section 129B may have access without committing an unforeseeable trespass, by a fine of not less than $2,500 nor more than $15,000 or by imprisonment for not less than 1 1/2 years nor more than 12 years or by both such fine and imprisonment.

(d) A violation of this section shall be punished, in the case of a rifle or shotgun that is a large capacity weapon, firearm or machine gun that was stored or kept in a place where a person younger than 18 years of age may have access without committing an unforeseeable trespass, by a fine of not less than $10,000 nor more than $20,000 or by imprisonment for not less than 4 years nor more than 15 years or by both such fine and imprisonment.

(e) A violation of the provisions of this section shall be evidence of wanton or reckless conduct in any criminal or civil proceeding if a person under the age of 18 who was not a trespasser or was a foreseeable trespasser acquired access to a firearm, unless such person possessed a valid firearm identification card issued under section 129B and was permitted by law to possess such firearm, and such access results in the personal injury to or the death of any person.

(f) This section shall not apply to the storage or keeping of any firearm, rifle or shotgun with matchlock, flintlock, percussion cap or similar type of ignition system manufactured in or prior to the year 1899, or to any replica of any such firearm, rifle or shotgun if such replica is not designed or redesigned for using rimfire or conventional centerfire fixed ammunition.