The Alexander Arms 17 HMR Upper Parts Kit, 18-inch, Black Cerakote Aluminum Receiver, M-LOK Handguard, Two Magazines (brand part number UST17) converts an AR-15 lower into a fast, flat-shooting rimfire rifle. Built by Alexander Arms, the kit pairs an 18-inch stainless barrel with a Black Cerakote aluminum receiver and M-LOK handguard, and runs on a blowback operating system appropriate for the 17 HMR cartridge rather than a standard gas-impingement AR action. It ships with an A2 flash hider installed, two 10-round magazines, and the parts kit needed to convert a standard AR-15 lower to run the rimfire upper. For shooters who already own an AR-15, it is a complete path to a dedicated rimfire trainer or varmint gun without buying a whole new rifle.

Key Specifications

• Chambered in 17 HMR, a fast, flat-shooting rimfire cartridge.
• Barrel length of 18 inches for added velocity from the rimfire round.
• Twist rate of 1:9 inches.
• Threaded 1/2-28 RH and ships with an A2 flash hider installed.
• Runs on a blowback operating system, appropriate for this rimfire chambering.
• Receiver is Black Cerakote aluminum with an M-LOK handguard.
• Barrel is stainless steel for accuracy and corrosion resistance.
• Includes two 10-round magazines and a parts kit for a lower conversion.
• Complete upper weighs approximately 4.5 pounds.

Frequently Asked Questions

What does this kit include? The 18-inch upper, an A2 flash hider, two 10-round magazines, and the parts kit needed to convert a standard AR-15 lower.

Why does it use a blowback action instead of gas impingement? The 17 HMR rimfire cartridge does not generate enough pressure to reliably cycle a standard AR gas system, so the upper uses a blowback design instead.

Buy the Alexander Arms 17 HMR Upper Parts Kit, 18-inch, Black Cerakote Aluminum Receiver, M-LOK Handguard, Two Magazines

Turn your AR-15 lower into a dedicated rimfire trainer with an AR15 upper kit built to run. Order it from our Lubbock, Texas gun shop, and our team will get it ready to ship as soon as it’s available.