Instructions
Gather all of the historical information about the gun and the time period it is from. Was it used in combat? If so, what war? Was it used by someone famous? The older the gun, the more money it could be worth. You can look up information about particular makes and models of guns online and in firearms books and magazines. A museum may be able to provide information about an antique weapon.
Check the gun's overall condition. Look for rust spots in the metal and scratches in the handle. Look carefully in the barrel for damage, too. Much of the damage done to a gun comes from over-cleaning. A gun should be cleaned only once after each shooting session.
Write down all of the information you have gathered from the first two steps. You will need to take it with you when you visit a professional appraiser to assess the gun's value.
Take pictures of the gun from every angle. The appraiser will need the photos to help authenticate the make and model and determine what it is worth.
Visit a gun appraiser and bring all of the information above. Check online or in the phone book for a gun shop in your area that can do the appraisal.
Sell your gun for the appraised value, plus the amount you paid the appraiser, which is usually about $20 for the first appraisal.