Alexander Arms AR-15 .17 HMR 18in Standard Upper Receiver 1-9 Twist 1/2x28 Thread Tacstar Carbon Fiber Handguard A2 Flash hider Black. 17HMR feature steel construction and a forge-turned barrel to produce high-end performance and accuracy. These AR15 Upper Receivers by Alexander Arms are built with a carbine-length gas system and equipped with a carbine-length buffer tube a one-piece handguard and a flash hider. Built on the AR15 platform these unfinished Alexander Arms .17HMR Uppers are compatible with standard AR15 lower receivers and you can install these upper receivers yourself. Alexander Arms has also updated the features on this upper to this: 1/2-28RH Threading Thread Protector (Upgrade Options Below) Lower Parts Kit Blowback Operating System Black Finish Two 10 round magazines. Buy an Alexander Arms .17HMR Upper Receiver to complete your .17HMR build for an accurate high performance firearm. Specifications for Alexander Arms AR-15 .17 HMR 18in Standard Upper Receiver: Manufacturer: Alexander Arms Caliber: .17 Hornady Magnum Rimfire Overall Length: 26 in Barrel Length: 18 in Gas System Length: Carbine Length Barrel Twist Rate: 1-9 Threads per Inch: 1/2x28 Muzzle Device: A2 Flash Hider Finish: Anodized Color: Black Gun Model: AR-15 Condition: New Fabric/Material: Steel Gun Type: Rifle Gun Make: AR Platform Gas System Type: Blowback Weight: 4.5 lb Magazine Included: Yes Dimensions: 4.65 X 10.00 X 37.75 in Features of Alexander Arms AR-15 .17 HMR 18in Standard Upper Receiver A2 Flash Hider LAR Alexander Arms Branded Hand Guard Standard Charging Handle Blowback Operating System Two 10-round magazines Package Contents: Alexander Arms AR-15 .17 HMR 18in Standard Upper Receiver Parts Kit for Lower Conversion What firearm models does the manufacturer say Alexander Arms AR-15 .17 HMR 18in Standard Upper Receiver is compatible with? The manufacturer suggests that Alexander Arms AR-15 .17 HMR 18in Standard Upper Receiver is compatible with AR-15Alexander Arms UST-17: AR-15 .17 HMR 18in Standard Upper Receiver 1-9 Twist 1/2x28 Thread Tacstar Carbon Fiber Handguard A2 Flash hider Black