So, forfeiture of the firearm is a consequence of the conviction (as defined in the terms of the plea agreement). The pardon nullifies that consequence.Seperate issue.
Think of the plea bargain as just another sort of contract. Remember the judge does *not* have to accept your guilty plea. I've personally seen it happen when the judge thought the defendent didn't understand fully or the plea was just too stupid/unfair for one party or the other.
Fill in the mad libs here: Your honor, if you accept my guilty plea I will do the following things: X, Y, Z.
It has nothing to do with your rights, or even if you're a felon, or not. It's simply what you promise to do in order for your plea to be accepted. A pardon has no effect on that. Imagine if a pardon was retroactive for an agreed upon jail sentence. You plead to 30 years. You do 10 and then get pardoned. The state doesn't owe you the 10 years back like a wrongful conviction, it just wipes away the 20 you have left.