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.
Key Highlights
- •Civilian MR-series update derived from HK416 architecture
- •Short-stroke gas piston eliminates carbon fouling in the receiver
- •Adjustable gas regulator tunes for suppressed or unsuppressed fire
Specifications
- Price
- $3,999
- Weight
- 7 lb 11 oz
- Calibers
- 5.56x45mm
- Rail Type
- mlok
Capability Profile
0-10 Scale Across 8 Axes
Compatibility Tags
Overview
The MR556 A4 is HK's current commercial MR-series update derived from HK416 architecture. The A4 brings fully ambidextrous controls, a slimmer M-LOK free-float rail, and reduced weight versus the legacy MR556A1. The short-stroke piston system runs cooler and cleaner than direct impingement, and the 2-position adjustable gas block 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)
- 2-position adjustable gas block for suppressed or unsuppressed use
- 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 $3,999 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"
- weight
- 7.67 lbs with empty 30-round magazine
- Gas System
- Short-stroke gas piston with 2-position adjustable gas block
- railSystem
- Slimline M-LOK handguard with 20.3" Picatinny top rail
- Trigger
- Two-stage, 4.5-5.6 lb approximate
- Twist Rate
- 1:7 right-hand, 6 lands & grooves
- threadPitch
- 1/2x28
- msrp
- $3,999
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