Googling about sentencing for assault I found this "A person who uses violence against another shall be punished by imprisonment for not more than two years, a fine not exceeding 5 million won, detention, or a minor fine."
So in that context 3 years being a 50% increase over the otherwise 2 year maximum seems fair enough to me.
IIRC for a some handguns this could actually work as long as you are actively pushing. Because if the barrel moves back a bit it will be out of battery blocking it from even firing.