This part shall not apply to:

(1) A peace officer of any duly authorized police agency of this state or of any political subdivision thereof, or a law enforcement officer of any department or agency of the United States who is regularly employed and paid by the United States, this state, or any such political subdivision, or an employee of the Department of Corrections of this state who is authorized in writing by the commissioner of corrections to transfer or possess such firearms while in the official performance of his duties;

(2) A member of the National Guard or of the armed forces of the United States to wit: the army, navy, marine corps, air force, or coast guard who, while serving therein, possesses such firearm in the line of duty;

(3) Any sawed-off shotgun, sawed-off rifle, machine gun, dangerous weapon, or silencer which has been modified or changed to the extent that it is inoperative. Examples of the requisite modification include weapons with their barrel or barrels filled with lead, hand grenades filled with sand, or other nonexplosive materials; and

(4) Possession of a sawed-off shotgun, sawed-off rifle, machine gun, dangerous weapon, or silencer by a person who is authorized to possess the same because he has registered the sawed-off shotgun, sawed-off rifle, machine gun, dangerous weapon, or silencer in accordance with the dictates of the National Firearms Act, 68A Stat. 725 (26 U.S.C. Sections 5841-5862).