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This is a Stripped M16 A4 Flattop Upper Receiver.
This forged 7075-T6 A4 AR upper is made to MIL-SPECS and hard coat anodized black for durability. Featuring machined T marks, and a mil-spec finish. These uppers are an overrun from a Mil-spec manufacturer for an M16 A4 Contract. The M16 A4 upper does not have M4 feedramps cut in the upper receiver as per mil-spec.
This upper would be perfect for that A4 clone or target build.