Heckler & Koch HK MR556A4 11″ 5.56 MLOK Upper Receiver Group
Now available separately as a standalone upper group that drops right onto your existing AR lower, providing the quality and legendary performance that Heckler & Koch is known for.
The latest update from HK-USA to the commercial variant of the legendary HK416, the MR556 A4 and MR762 A4 represent an enhanced example of “no compromise” HK performance.
Its short-stroke gas piston operating system does not impart hot carbon fouling back into the action, allowing the weapon to run longer, with less maintenance and with less wear on internal components than direct-impingement ARs. Its adjustable gas regulator allows the operator to tune the action specifically for suppressed or unsuppressed operation. Fully ambidextrous controls, lighter weight and a slimmer profile make the new A4 easier to operate, manipulate and employ.
For those who demand an AR with unmatched capability and uncompromising reliability and durability, the MR A4s remain the top tier solution.
Complete upper receiver group with barreled upper, bolt carrier group, charging handle, HK heavy buffer and buffer spring. Compatible with only carbine receiver extensions and not A5 or rifle extensions.
Compatibility Note: These uppers utilize a firing pin safety in the bolt carrier group to prevent the possibility of a slamfire. These uppers will not work with certain types of triggers. Please visit this HKPRO thread to check trigger compatibility, here.
Specifications
- Caliber: 5.56mm
- Color: Black
- Upper Receiver: Forged, HK MR556A4
- Bolt Carrier Group: MR556A4
- Rail: MLOK
- Barrel: 11″ Cold Hammer-Forged Barrel, 1:7 Twist
- Gas System: Short-Stroke Gas Piston
- Gas Block: Adjustable
- Charging Handle: HK Ambidextrous
- Muzzle Device: Birdcage
- Buffer Assembly: HK Heavy Buffer
Mark S. (verified owner) –
SOL for President!! Been waiting on this puppy and had in fact, just emailed them asking if it would come back in stock anytime soon. They said “we sure hope so” but couldn’t say when. A week later I get a notification IN STOCK!!! Other site notifications typically don’t work at all or you get the notification a week+ after the item came back in stock. They shipped it out immediately as usual and I’m thrilled with the upper and Rooftop Defense is the shizzle!!
Andrew P. (verified owner) –
Fantastic price on soon to be unobtainium… Had to splurge to get my dream rifle.
On a griffin mk 2 ambi lower with the geissele mr556 trigger and couldn’t be happier.