Only listing here because I no longer have box it came in. This is an AS NEW (I bought it new last year - never used it - mounted it on a lower and stuck it away) FACTORY Adams Arms carbine piston upper. This is not an M4 configuration upper in that it doesn't have the barrel stepdown. I installed an aftermarket CAR type flash hider to replace the A2 flash hider that it came with (I can change it out if you want). Its a slip over the barrel type CAR flash hider with the internal threads just behind the flash hider slots. It attaches with a standarad crush washer. Barrel is 16.1" without the flash hider (I believe). I think the twist is 1/7. This is a NEW upper - $525 shipped. I'm selling because I find that I use my SP1 with its 1/12 twist to shoot 55gr ammo. This is jut a little to front heavy for my taste. This is a flattop over (including over the gas block)
Photos are available.
Here is the Adam Arms link on my upper - I guess its referred to as a Mid Length Base model