Spikes Tactical Upper 5.56 11.5in FN CHF w/7in SAR3 Rail & FSP. We maintain our high standard of tolerances and attention to detail as the uppers we use for complete rifle builds. Every built upper and complete gun is test fired before leaving our facility for function check before it reaches you. We offer several rail choices and rail lengths. Use the drop bar to make your selection. Specifications for Spikes Tactical Carbine Cold Hammer Forged 11.5in Upper Receiver: Manufacturer: Spikes Tactical Caliber: 5.56x45mm NATO Barrel Length: 11.5 in Finish: Anodized Color: Black Condition: New Magazine Included: No Country of Origin: USA Features of Spikes Tactical Carbine Cold Hammer Forged 11.5in Upper Receiver: SAR3 Rail Forged Upper Receiver 7075 T6 Construction Forward Assist Ejection Port Door Ejection Port Door Spring Ejection Port Door Rod 11.5in Cold Hammer Forged Barrel M249 SAW Chrome Lined Spec DIN 21CrM0V511 Light Weight Profile 1/7 Twist Rate 1/2 X 28 Thread Pitch for Muzzle 5.56 Nato Chamber .625 Gas Block Seat M4 Feed Ramped Barrel Extension Mil-Spec Phosphate Coating 7in SAR3 Rail 7075 T6 Barrel Nut 6061 T6 Rail Continuous Top Rail Free Floating 1 Piece Q.D Attachment Points A2 Front Sight Base Pinned Front Sight Post FSP Detent FSP Detent Spring Carbine Gas Tube Black Nitride Inside and Out Gas Tube Roll Pin Charging Handle Forged Aluminum Mil-Spec Type 3 Coating Phosphate M16 Complete BCG Phosphate Coated Laser Engraved with ST Spider logo High Pressure Tested (HPT) Magnetic Particle Inspected (MPI) A2 Flash Hider 1/2in Crush Washer Package Contents: Spikes Tactical Carbine Cold Hammer Forged 11.5in Upper Receiver What firearm models does the manufacturer say Spikes Tactical Carbine Cold Hammer Forged 11.5in Upper Receiver is compatible with? The manufacturer suggests that Spikes Tactical Carbine Cold Hammer Forged 11.5in Upper Receiver is compatible with M4 AR-15Spikes Tactical STU5310-CQ7FP: Upper 5.56 11.5in FN CHF w/7in SAR3 Rail & FSP