Aero Precision APAR700201C M4E1 Threaded Receiver 5.56x45mm NATO 7075-T6 Aluminum Black Anodized Receiver for AR-15 $134.99
Spikes SFT50M4 Flat Top Stripped Upper Multi-Caliber 7075-T6 Aluminum Black Anodized Receiver for M4 Platform $103.50