1) if you read the whole thing you can only turn in 1 gun, and that credit gets split over 2 tax years.
2) Tax credits are not the same as deductions. A $2000 tax credit means you are getting 'credit' for having paid $2000 of the tax you would otherwise owe. Hence $2000 is $2000.
Regardless, this is a stupid idea and there's no chance it will be passed.