The Heckler & Koch MR762 A4 Complete Upper Receiver Assembly is a cold hammer-forged 7.62x51mm upper built on the proven short-stroke piston system that powers the HK417—the rifle trusted by military and law enforcement worldwide. This 16-inch upper receiver assembly ships ready to pair with an MR762 lower receiver, giving precision shooters and hunters a modular platform that eliminates the fouling and reliability issues inherent to direct-impingement designs. The closed piston system keeps hot gases and carbon out of the receiver, translating to cleaner operation, easier maintenance, and the consistency serious marksmen demand.
Every component is engineered to HK specifications: a cold hammer-forged barrel, complete bolt group, tungsten-filled buffer, adjustable gas block, and the signature HK Free Floating Rail System handguard for repeatable accuracy and accessory mounting. The extended convertible charging handle gives you control whether you run right or left, and the forward assist ensures positive lock every time. The upper arrives in an HK soft case, ready to install on your lower receiver.
Because this is an upper receiver assembly only—not a complete firearm—it ships without requiring an FFL, making it easy to order and receive. It's the perfect foundation for a long-range hunting rifle, precision rifle platform, or tactical build where reliability and accuracy are non-negotiable. MR762 lower receivers are sold separately.
| Caliber | 7.62x51mm NATO |
| Barrel Length | 16 inches |
| Barrel Type | Cold hammer-forged steel |
| Upper System | Short-stroke piston (closed) |
| Handguard | HK Free Floating Rail System |
| Charging Handle | Extended convertible (ambidextrous) |
| Gas System | Adjustable gas block |
| Buffer | Tungsten-filled HK proprietary |
| Included Components | Complete bolt group, buffer spring, charging handle, forward assist |
| Shipping Case | HK soft case |
No. This MR762 A4 upper is designed exclusively for HK MR762 lower receivers. It is not compatible with standard AR-10 lowers or other manufacturer platforms. You will need an MR762 lower to complete the rifle.
No. Because this is an upper receiver assembly only and not a complete firearm, it can be purchased and shipped without a Federal Firearms License. You will need an FFL to receive the MR762 lower receiver separately.
The HK short-stroke piston system is a closed system that routes hot gases and carbon away from the receiver and bolt carrier, rather than forcing them directly into the action. This dramatically reduces fouling, malfunctions, and maintenance burden—the same advantage that made the HK417 the rifle of choice for elite military and law enforcement units.
Yes. The adjustable gas block allows you to tune the system for suppressed or unsuppressed fire, making it adaptable to different shooting scenarios and accessories.
Heckler & Koch
Rock River Arms
