Brand: HM Defence Technology
Model: 12.5MBUP
Caliber: 223 Rem/5.56 Nato
Platform: AR-15
Barrel: 12.5", 4150 Chromoly
Color: Black
Finish: Cerakote
Gas System: Mid-Length
Muzzle Device: Muzzle Brake
Muzzle Thread: 1/2-8
Twist: 1:8
Receiver: Mil-Spec 7075-T6 Aluminum w/ Type III Class II Anodized
Handguard: 10 3/8", 6061-T6 Aircraft Grade Aluminum
Attachment Style: M-Lok
BCG: HMB Bolt
Charging Handle: Yes
Weight: 3lb 14oz

Features

The HM Defense Monobloc Upper sets a new standard for precision, reliability, and innovation in AR-platform performance. Featuring a triple-honed, button-rifled monobloc barrel, this upper delivers exceptional accuracy and consistency. The integrally machined gas block is built directly into the barrel, eliminating the need for aftermarket alignment and ensuring superior barrel harmonics for tighter groupings and enhanced shot placement.

Engineered for dependable performance in extreme conditions, the upper includes Mil-Spec M4 feed ramps for reliable cycling. Unlike standard M16 and AR-15 bolts that are prone to failure at the cam pin hole, the HMD bolt uses a cam pin socket design to eliminate this weak point—dramatically increasing durability and reducing the risk of breakage under heavy use. Best of all, the HMD bolt is non-proprietary, making it a versatile upgrade compatible with your other AR-15 builds. Whether for duty, defense, or precision shooting, the HM Defense Monobloc Upper is built to outperform.

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Shipping Restrictions

It is the customer’s responsibility for understanding state laws regarding all purchases made. For a comprehensive list of all Shipping Restrictions, please refer to our Shipping Restrictions By State Page found Here.

All NFA Rules Apply

These items are controlled by the U.S. Government and authorized for export only to the country of ultimate destination for use by the ultimate consignee or end-user(s) herein identified. They may not be resold, transferred, or otherwise disposed of, to any other country or to any person other than the authorized ultimate consignee or end-user(s), either in their original form or after being incorporated into other items, without first obtaining approval from the U.S. government or as otherwise authorized by U.S. law and regulations.

Local Law Compliance

Certain firearm parts and accessories, including AR-style upper receivers, are subject to complex and frequently changing federal, state, and local laws and regulations. While an upper receiver may be lawfully sold and shipped as a component, the legality of possessing, assembling, configuring, or using an upper receiver in certain states (e.g., California, Washington State) and localities depends on how it is assembled, combined with other components, and ultimately used. You are solely responsible for ensuring that any assembly, configuration, possession, or use complies with all federal, state, and local laws, including any so-called “assault weapon” bans and short-barreled rifle restrictions. We do not provide legal advice and are not responsible for unlawful configurations or uses.