Whoever willfully, intentionally and without right, by the explosion of gunpowder or of any other explosive, unlawfully damages or destroys property or injures a person, shall be subject to the following penalty:
I. If the offense occurs prior to November 1, 1973, he shall be fined not more than $1,000 or imprisoned in the state prison for not more than 20 years, or both.
II. If the offense occurs on or after November 1, 1973, he shall, if a natural person, be guilty of a Class A felony, and any other person shall be guilty of a felony.