My wife gave me a Bushmaster AR15 Shorty A2 for Christmas. I wanted an A3, but none could be found at the time. I've never fired the gun, and I'd like to take it to a gun show here in Fort Worth this weekend and trade it for an A3. Given that I've never used it in any way and have all the original packaging, what percentage of the current value could I reasonably expect to receive in trade with a dealer for an A3?