If you’re charged with violating a gun law here in Massachusetts, prosecutors usually must get a certification from the State Police Crime Lab confirming that the gun at issue is functional, i.e., capable of firing.
According to G.L. c. 140, Sec. 121A,
A certificate by a ballistics expert of the department of the state police or of the city of Boston of the result of an examination made by him of an item furnished him by any police officer, signed and sworn to by such expert, shall be prima facie evidence of his findings as to whether or not the item furnished is a firearm, rifle, shotgun, machine gun, sawed off shotgun or ammunition, as defined by section one hundred and twenty-one, provided that in order to qualify as an expert under this section he shall have previously qualified as an expert in a court proceeding.
The Crime Lab will also measure the barrel of the gun and include the barrel’s length (along with an “associated estimation of measurement uncertainty) on the certificate.
Under the state’s statutory law (G.L. c. 140, Sec. 121) a “firearmā is āa pistol, revolver or other weapon” with a barrel length under 16 inches. A ārifleā is a weapon having a rifled bore with a barrel length equal to or greater than 16 inches. And a “shotgun” is a weapon having a smooth bore with a barrel length equal to or greater than 18 inches with an overall length equal to or greater than 26 inches.