IANAL, but I took "without permission" as a condition of the machine gun clause, which seems to stand seperate from the sawed-off shotgun clause of the relevant chapter.
clause 1: Whoever, except as provided by law, possesses a machine gun, as defined in section one hundred and twenty-one of chapter one hundred and forty, without permission under section one hundred and thirty-one of said chapter one hundred and forty;
clause 2: or whoever owns, possesses or carries on his person, or carries on his person or under his control in a vehicle, a sawed-off shotgun, as defined in said section one hundred and twenty-one of said chapter one hundred and forty
shall be punished by imprisonment in the state prison for life...
I could be wrong. As I said, it's just the way that I, as a layman, took it to mean. Anyone else care to take a shot at it?