I have a used but in great condition Fostech Complete AR-15 Lower with Echo II Trigger. The only markings on it are near the front takedown pin where the handguard rubs it. The upper is an Aero Precision M4E1 Enhanced 16in 300bo that has less than 30 rounds through it. Has a Geissele Airborne Charging Handle and a Rise Armament BCG. I can remove the Vortex Crossfire 1-4 and sell it for $850. The handguard bumps against the lower so if you want to break the rifle down you will have to remove both takedown pins. I tried other uppers that I have, and it only does it with the Aero uppers.