The Trustee will "own" everything you have on the day you file, including any right to rebuy your guns. But if the Trustee would have to pay full value, he will abandon that right. List the "right" to rebuy with your assets. Be prepared to answer questions. If you've reserved the right to rebuy, it indicates the guns have value, otherwise, they could be some bubba'ed up junk, not worth much
If you have NOT filed, you can sell for full value and spend the money on lottery tickets, or beer, or anything that you consume and then file.
If you HAVE ALREADY filed, then you'll have to negotiate with the Trustee. It usually is not worth it for a Trustee to administer a small asset, he has to pick it up from you, sell it, (while complying with all gun laws) and then do paperwork, then keep a small commission, and send out a proof of claim to creditors, review these documents, reprot to the Court, and then send each creditor a proportionate amount of the proceeds of the sale. I've gotten them to abandon things like small boats and fishouses because of the cost and hassle.
It's easiest for him to sell the guns back to YOU. Start with a low offer, maybe $200. He'll have to sell them wholesale and will only want to devote a few minutes to making the arrangements, unless he's a gun guy who enjoys complicated non-lawyer work. He might make $40 for this work. And for just a couple hundred dollars some Trustees will simply abandon. They like to recover assets in the thousands at least.