I have had charges reversed on me as well ...though nothing in the neighborhood of a firearm. Paypal is not the one screwing you, it's the buyer. The transaction was reversed at his request ...no matter what he's telling you. You are not covered under their protection policy, since you did not send to his verified address.
My reversal was only for $50, so I argued a little, then swallowed it. I would encourage you to continue arguing the matter, since I would guess your amount is more along the lines of $700+.
One question: Has Paypal removed the reversed funds from your bank account / credit card yet? ...or just your Paypal account?
If it's just your Paypal account, I encourage you to close the bank or credit card account <linked to your Paypal account> immediately ...before they take real money from you.