The Mike-15 Gen 2 Upper Receivers allow consumers to use their existing AR style Mil Spec Lower Receiver and combine it with the included Picatinny Rail Adapter and they can convert their vanilla M4 to a modern Buffer-less firearm, capable of using a collapsible or folding stock. Specifications for FM Products MIKE-15 Buffer-less .223 Wylde Gen 2 Upper Receiver: Manufacturer: FM Products Cartridge: .223 Wylde Barrel Profile: Light Weight Gas System Length: Mid Length Barrel Twist Rate: 1-8 Threads per Inch: 1/2x28 Handguard Type: Free-Float Muzzle Device: A2 Finish: Type III Hard Coat Color: Black Fabric/Material: 41v50 Steel Gas Block Journal Size-Diameter: .625 in Gun Rail: M-LOK Charging Handle Included: MIL-SPEC Magazine Included: No Mount Type: M-LOK Features of FM Products MIKE-15 Buffer-less .223 Wylde Gen 2 Upper Reciever: Proprietary Low Mass Bolt Carrier machined from pre-hard 4342. The carrier key (gas key) has an integrated recoil lug, which has a mating pocket in the proprietary bolt carrier.  This ensures no recoil load during cycle is distributed to the gas key screws. The Lightweight M-Lok compatible handguard has an interlocking tab with the upper receiver, ensuring proper alignment with the bore. Two Torx bit screws hold the handguard in place for simple maintenance without risk of stripping screws. Proprietary double pinned gas block with interlocking feature, ensures proper alignment of gas block. The Gas Block has its gas port drilled from the top, so we can confirm alignment of gas port in barrel, port in the gas block and gas tube are all aligned prior to assembly. Monolithic Style lightweight sleek modern buffer-less Ar style Upper Receiver, simple elegant direct impingement operating system allowing customers to use the included picatinny rail adapter to transform their vanilla M4 into a Modern Buffer-less AR. Extra long, and lightweight Taper Lock barrel nut improves torsional support to longer handguards during hard use. Taper Lock Barrel nut, and extra-long lightweight Barrel nut, allow for excellent handguard rigidity and accuracy in a lightweight package. Proprietary Firing Pin Spring, using S7 Tool Steel Firing Pin, and S7 Tool Steel Extractor Pin.  An S7 Tool Steel Round Cam Pin and S7 AR-15 Extractor are also utilized. Package Contents: FM Products FM-15 .223 Wylde Mid Length Gen 2 Upper Reciever Picatiny Rail