Heckler & Koch HK MR556A4 16″ 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: 16.25″ 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
Johnny –
10/10 HK craftsmanship. Stellar service. Great price!
D (verified owner) –
Super easy and fast and shipping great deal
Ramis A. (verified owner) –
Excellent product, came with HK rifle case.
Excellent seller, fast shipping.
Hannah N. (verified owner) –
I ordered the HK Upper a few weeks ago. Today, I finally shot the HK Upper MR556A4 16″, using my Huldra Mark IV lower. It is very accurate. I was getting about 1/2″ MOA at about 100 yards. I was amazed. The recoil felt less, compared to my other AR Uppers, because of the Tungsten core recoil buffer that comes with the HK Upper. This HK A4 Upper has a lifetime barrel replacement, which is nice. So, I will have to plan on shooting massive amounts of ammo. Very good communication with owner of Rooftopdefense. I will be shopping from them again. Thank you!
Rick G. (verified owner) –
The HK upper is 10/10. I own several home builds and factory rifles, this is up there with my favorite. The review is mostly about the service at Roodtop Defense. I’ve purchased a wide variety of parts from them, and I’ve never been close to dissatisfied with the communication, updates, packaging and condition of things I’ve bought. We can all choose who we buy from, this company deserves your business.