I possess a bill of sale for a firearm that I purchased in 2009. Later that year, my ex-girlfriend took possession of the firearm. Now, I have requested that she return the firearm to me. She is of legal age to possess the firearm, but has no documentation to support ownership. The first owner of the firearm will agree to the facts stated in the bill of sale. I am willing to pursue a civil lawsuit. What type of law would support my lawsuit? Do I have any other options? Thanks!