So we have a murderer, in Florida, that was intent on killing as many innocent children as possible and the idea here is to tax ammo to stop these murder sprees? Make the ammo so expensive that only rich people can afford to commit murder? I know I'm not all that smart, but I don't get it.
That premise was the subject of jokes by Chris Rock at a stage show once. It's on youtube but don't want to post the link here, as he uses profanity, and don't want to violate any rules. It's easy to find however by searching "Chris Rock on gun control" The basic premise is he's opposed to gun control, and likes guns. He then says what we need is bullet control. If bullets cost $5 grand a piece, there'd be no more innocent bystanders.
When it comes to self defense, in many places in the country, we already have a financial penalty for shooting, in a way. It's not 5 grand a bullet either. There's an old saying, "Every bullet comes with a lawyer attached" is true in some places. If you shoot in self defense, there is the possibility that it's going to cost you a lot of money. I know it's an extreme example, but the total amount of legal spending on the Zimmerman case allegedly was 10 million dollars, and for what? That's the criminal side only, not civil. There have been many others where the criminal side expendature costs totaled one million dollars. It cost 50 grand just to get a good self defense lawyer to start to take your case in some places.
Real criminals however, don't care about taxes. Even if they were to pay them, it's just the cost of doing business.