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
William P. (verified owner) –
The upper is an incredible hard use tool as you would imagine coming from HK. Rooftop defense did an amazing job getting this to me with insanely fast shipping. They have set the new standard and have earned a repeat customer for life.
Lance M. (verified owner) –
Rooftop Defense is always top notch with super fast shipping and tracking info. The HK upper arrived well packed in great condition and got it at a good price. Thanks Sol!
My wife also gets a kick out of the Ramen and the note.
Walter R. (verified owner) –
This is more of an “initial thoughts” than actual review, but I think this upper is excellent. Being a short stroke piston adds some weight, but it’s short enough that even fully equipped and hanging a 1lb inconel suppressor off the end – it feels light and maneuverable. I’m very happy they went 11″ instead of 10.4″ they hit the sweet spot. Fit and finish is excellent, very comfortable, shoots flawlessly out of the box. Much lighter than a comparable A1. Important note though – I have two LWRC lowers both purchased here. One has a MR556A1 upper on it which I slapped on and fit perfectly. This upper however, did NOT want to go on. It took me awhile to realize there’s a rubber plug in the lower for preventing rattle with some uppers. You will need to remove that plug for this upper to fit. Other lowers may use tensioning screws which you will likely need to loosen to allow proper fitment.
Brian P. (verified owner) –
I had a fantastic experience with Sol! His customer service is top-notch and super friendly, helpful, and quick to respond to all my questions about the product.
Alex B. (verified owner) –
Awesome upper and impressive service. I literally got the upper within 48 hrs delivered to my door! I would definitely buy again from Rooftop defense.
PS: I did eat the noodles !!!!