Make sure choke tubes come out. Rusted-in or stuck chokes can cost a couple hundred dollars to remove and are a sign the gun has been neglected.
Look down the bores for pitting. ou might decide to live with very light pitting or have it polished out, but deep pits are deal breakers.
Make sure the barrels are fluid steel, not Damascus. To identify Damascus steel, look for swirl patterns or the stamped words "twist," "laminated" or "Damascus." Unless you're an expert in metals, stay away.
Look for safe scars. Check the toe of the stock, where it would bang into the bottom of a safe, and the sides of receivers, which can be marred by the bolt handle of the neighboring gun.
Inspect barrels for dents. Dents are dangerous but can be fixed. Bulges are very dangerous and also tend to be very expensive to repair.
Look where wood meets metal. Wood that is flush with the metal or below its level means the gun has probably been refinished.
Ring the barrels. Take the gun apart and hang the barrels on your finger from the underbolt or forearm hook. When you thwack them, you should hear a clear, bell-like tone. A "thunk" means side or top ribs need resoldering, a job necessitating the expense of rebluing.
Look for cracks in the stock. Check around the tang, in the head of the stock and in the wrist. Forearms can crack, too. Cracks should be repaired before you shoot the gun.
Check the stock dimensions. Many older guns, especially American doubles, have lots of drop, making them very difficult to shoot well. You're looking at a few thousand for a new stock to make the gun shootable.
Take pumps and autos apart. If the magazine cap is rusted on, the insides have probably been neglected. Look for rust and missing rings on semiautos, underneath the forearm.
Check the screws. Buggered slots mean an amateur has been poking around inside the gun. Also, engraved screws on higher-end guns are expensive to replace.
Check for wear by looking at a double gun's lever. On new guns, the lever angles to the right and gradually moves to six o'clock. If it's past that point, it's time to tighten the action.
Bring snap caps and try the trigger. If the trigger's heavy, deduct the price of a trigger job (usually under $100) from your offer. If the gun is an older double, the price of trigger work goes up to a deal-breaking amount. Make sure the ejectors work, too.
Wiggle the barrels. If the barrels wiggle with the fore-end off, the action needs tightening, which can run you a couple hundred bucks.
Check chamber length. Chamber length should be stamped on the barrel. Chambers may be shorter than standard, especially on older 16 gauges. On many guns, the chambers can be lengthened.