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Heckler & Koch

HK MR556 A4 16.5"

HK's commercial semi-auto HK416. Short-stroke gas piston with adjustable regulator, ambi controls, M-LOK free-float rail.

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Key Highlights

  • •Civilian semi-auto HK416 (the rifle the U.S. SOCOM, USMC IAR, and German KSK run)
  • •Short-stroke gas piston eliminates carbon fouling in the receiver
  • •Adjustable gas regulator tunes for suppressed or unsuppressed fire

Specifications

Price
$4,299
Weight
7 lb 11 oz
Calibers
5.56x45mm
Rail Type
mlok
Best For
duty patrolhome defenseoutdoor defensecompetition

Capability Profile

0-10 Scale Across 8 Axes

Compatibility Tags

family: modern-riflefamily: ar-patterntrigger: ar-fcginterface: picatinny-tophandguard: mlokbarrel: longthread: 1/2x28mag-type: stanag

Overview

The MR556 A4 is HK's commercial, semi-automatic version of the HK416 — the same short-stroke gas piston rifle adopted by U.S. SOCOM (as the M27 IAR variant for USMC and the URG-I for Delta/SEAL teams), the German KSK, and Norwegian Special Forces. The A4 is the current-generation update with fully ambidextrous controls, a slimmer M-LOK free-float rail, and reduced weight versus the legacy MR556A1. The piston system runs cooler and cleaner than direct impingement, and the user-adjustable gas regulator lets you tune the action for suppressed or unsuppressed shooting without changing parts. This is the gold-standard piston AR if budget is not the constraint.

Key Features

  • 16.5" cold hammer-forged barrel, 1:7 twist, 1/2x28 threads
  • Short-stroke gas piston operating system (HK416 pattern)
  • User-adjustable gas regulator (suppressed/unsuppressed/adverse)
  • Fully ambidextrous controls (safety, mag release, bolt catch)
  • HK Free Floating M-LOK Rail System with full-length top Picatinny
  • Tungsten-filled HK proprietary buffer and recoil spring
  • Extended convertible charging handle
  • Accepts standard STANAG / AR-15 magazines

Pros

  • +Civilian HK416 — proven combat-spec gas piston system
  • +Adjustable gas regulator is rare at any price point
  • +Cleaner running than DI, especially when suppressed
  • +Excellent QC and tight tolerances out of the box
  • +Ambidextrous controls work cleanly (no afterthought conversions)
  • +STANAG mag compatibility and AR-pattern lower controls

Cons

  • −MSRP $4,299 puts it well above premium DI ARs
  • −Heavier than comparable DI rifles (7.67 lbs unloaded)
  • −Proprietary barrel, BCG, gas system, and handguard (no DI parts swap)
  • −Limited aftermarket beyond HK and Geissele (who supplies HK)

Detailed Specifications

caliber
5.56 NATO
Barrel Length
16.5"
Overall Length
33.25" - 36.5" (adjustable stock)
weight
7.67 lbs (unloaded, no magazine)
Gas System
Short-stroke gas piston (adjustable regulator)
railSystem
HK Free Floating M-LOK Rail System (20.3" Picatinny top)
Trigger
Single-stage AR-pattern (mil-spec compatible)
Twist Rate
1:7 right-hand, 6 lands & grooves
threadPitch
1/2x28
msrp
$4,299

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