The HK Complete Gas Piston (HK part no. 50205381) is a factory-original replacement piston built to Heckler & Koch‘s exacting tolerances for the 5.56x45mm MR556A1 and 7.62x51mm MR762A1 short-stroke gas systems. Manufactured in Germany from durable steel, it arrives fully assembled with the three locking piston rings already installed, so it drops straight into service without additional fitting. HK’s short-stroke piston design routes hot gas and carbon fouling out of the action instead of back into the receiver, extending the rifle’s reliability between cleanings compared to a standard direct-impingement AR. This is the same complete piston HK specifies for both the MR556A1 and the MR762A1, making it a smart spare to keep on hand for either rifle.

Key Specifications

• Fits the MR556A1 and HK416 platform chambered in 5.56x45mm/.223 Remington.
• Fits the MR762A1 and HK417/G28 platform chambered in 7.62x51mm/.308 Winchester.
• Machined from durable steel and manufactured in Germany to factory HK tolerances.
• Supplied as a complete piston assembly with all three locking piston rings pre-installed.
• Uses HK’s short-stroke piston operating system, keeping carbon fouling out of the receiver for easier maintenance.

Frequently Asked Questions

Does this piston fit both the MR556A1 and the MR762A1? Yes, HK uses this same complete gas piston assembly across the MR556A1, MR762A1, HK416, HK417/G28, and G36 platforms.

Is this a genuine HK factory part? Yes, it is an OEM piston manufactured in Germany and supplied complete with the locking piston rings already installed.

Buy the HK Complete Gas Piston, MR556A1 and MR762A1 Compatible

Keep a genuine HK spare piston on hand and you will never lose range time to a worn factory part. Order this complete gas piston from our rifle parts selection and Schaefer Defense will ship it fast, direct to your door from our Lubbock, Texas gun shop.