So I am considering selling my Ruger .480. It has a 7 1/2" barrel and has the matte grey finish. The problem with selling it is that I have no idea what it's worth. Please don't say it's worth what someone is willing to pay because that is obvious. I see one on Gun Broker sold for $635 in March and another sold for $624 last month. I was thinking $600, so what are your thoughts?