I have for trade only a Core 15 AR upper that I would like to trade for an 18" mid length upper. This upper has had a total of 5 rounds fired through it. The barrel is 16" with 1/9 twist. Barrel and chamber are chrome lined. Carbine length gas tube with A2 post sight. Trade only for a similar condition upper with an 18" barrel and mid length gas system. The photo is stock but it looks exactly the same. Thanks for looking.