Snared

I think the best solution is to shoot back and see where it hits.

So you played your drum for him, you played your BEST for him, then he shot at you, you and your drum (pa rum pum pum pum)? That's rough, drummerboy.

Don't sound dampers for drums exist for this very reason?

You can sue them

Someone gets to pay for some new heads/shells

Send them a bill for the brand new, super expensive evan's bass drumhead that you're obviously going to need to replace the one they shot out.

Boy you sure know how to drum up attention

Coming onto your property and damaging things that you own that is illegal. You can press charges.

Look into noise ordinances, so that you know whether you are breaking them or not. If you aren't, post it somewhere as a reminder that you are within the limits of the law. That said, in regards to the air gun- legal action. Take it. They had no legal right to point a gun at your property, let alone fire at it. I'm fairly certain that breaks several laws and is grounds for criminal investigation. I also think it could be a civil suit if l criminal investigation gets you nowhere.

How does playing in a garage with the door open produce less noise than playing inside the house in your room?

You are on your OWN property! Unless they've filed a noise complaint with the police or have spoken to you repeatedly requesting you to keep it down, then this reaction seems more than just a bit extreme. Maybe leave a note taped to their front door along with some ear plugs and a phone number for anger management.

Go to the musical instrument store and have them print out a receipt for the most expensive drum you can buy. Deliver this receipt to the neighbor and demand payment. Let him stew about it for a day or two and then ask for the real amount.