HK MR556 A4 vs Romanian md.63: The Shop Defense Gun

What the HK MR556 A4 is

The MR556 is Heckler & Koch’s semi-automatic rifle for the civilian market. American Rifleman puts it plainly: “The MR556 and MR762 are civilian versions of the HK416/417.” The civilian MR556 was introduced in 2009, and the A4 series is the updated line HK-USA announced in late 2024.

Inside, it runs like the HK416: a multi-lug rotating bolt driven by a short-stroke gas piston, so the gas that cycles the action pushes a piston rod instead of being piped back to the bolt carrier the way a direct-impingement AR-15 does. According to American Rifleman, the factory A4 adds an adjustable gas block for suppressed and unsuppressed shooting, ambidextrous bolt and magazine releases, an ambidextrous charging handle, a 45-degree safety on both sides, and a cold hammer-forged barrel with a 1:7 twist and a muzzle threaded 1/2×28. The factory handguard is a slimline M-LOK design; the tan handguard on ours has keyhole-shaped slots instead, so not every part on our rifle is the factory A4 configuration.

### Reading the receiver

The left side of the lower is marked with the HK logo, MR 556 A4 and 5.56 mm x 45. Beside it is the ambidextrous safety, whose positions are shown by pictograms rather than letters: a red cartridge for fire and a crossed-out cartridge for safe. The right side of our lower reads Heckler & Koch Inc. Columbus, GA.

The kit on the HK MR556 A4

The rifle in the video carries a main optic with a small red dot on top, a laser box, a weapon light and a suppressor. Here is what each of those is.

### The 1x/4x optic

The big optic is a dual-role sight: instead of zooming through a range, it has two settings, 4x and 1x, and changes between them with a single throw of a lever. The 4X and 1X markings for that lever are on the body. Ours sits in a quick-detach rail mount.

### The red dot on top

Mounted on top of the 1x/4x optic is a small open reflex sight, marked Made in Germany, with an owl logo.

### The laser box

The tan box on the top rail ahead of the optic is shaped like the U.S. military AN/PEQ-15, also called ATPIAL. Wikipedia describes the PEQ-15 as “a multi-function infrared target pointer and illuminator”: it combines a visible red laser, an infrared laser for aiming through night-vision goggles, and an infrared illuminator, a light only night vision can see. It entered service in 2003. That is background on the military unit. The label on ours reads “MULTIPLE LASERS: VIS IR,” but we have not confirmed its maker, model or functions, so we call it PEQ-style.

### The light and the suppressor

Under the laser box, on the side of the handguard, is a weapon light, with its cable running back along the top rail. Out front, mounted on a black adapter, is a suppressor. Federal law defines a silencer as a device for “silencing, muffling, or diminishing the report” of a portable firearm, and the National Firearms Act lists any silencer as a firearm in its own right, so it is a federally regulated NFA item.

What the Romanian md.63 is

The md.63, in full Pistol Mitralieră model 1963, is Romania’s licensed derivative of the Soviet AKM. The first production model appeared in 1963. It was made primarily at the Cugir Arms Factory in Alba County, with some production from the 1970s at Uzina Mecanică Sadu. Wikipedia says the md.63 “was initially indistinguishable from the Soviet AKM.” Export rifles were designated AIM md.63; the folding-stock md.65 followed in 1965.

The AKM itself was introduced in 1959 as a lighter successor to the AK-47. Its receiver is stamped from 1.0 mm sheet steel, where the AK-47 it replaced used a receiver machined from a solid block, and its action uses a long-stroke gas piston permanently attached to a large bolt carrier. It became the most widely produced variant of the Kalashnikov series, and Romania’s md.63 is one of its local versions.

How to spot a Romanian md.63

### The foregrip

The feature most people notice first is the vertical wooden grip on the lower handguard. According to Wikipedia, Romania added this laminated wooden foregrip to the md.63 in the mid-1960s to help riflemen control vertical muzzle climb in automatic fire. Not every Romanian AK has one: early md.63s did not, and the folding-stock md.65 was first made with traditional AKM-pattern handguards. Handguards can also be swapped, so the grip alone does not identify a whole rifle. On ours, it is where the “NO ONE IS SAFE” sticker lives.

### The markings

Wikipedia says each military md.63 and md.65 receiver was marked on the left with the year of production and a serial number with a Latin letter prefix. Ours is a semi-automatic built on a U.S.-made receiver from Romanian md.63 parts. At the front of the left side, above the rivets, it carries a stamp reading 1987 and a lettered serial, which we have blurred in our photos. A date like this belongs to the part it is stamped on; it is not the build date of the whole rifle.

On military md.63s, Wikipedia lists three selector markings on the right side: S for safe (“Sigur”), FA for automatic and FF for semi-automatic. Ours, a semi-automatic, shows a stamped S at the top of the selector’s travel.

### The rest of the AKM pattern

The rest is familiar AKM: a stamped receiver, a wooden handguard and buttstock, a curved steel magazine and iron sights. There is no optic and no rail. Ours also has a leather sling.

The stickers, one by one

The second half of the video stops on each sticker long enough to read it. We put all of them on ourselves, along with the hand-written LIVE MAG 1 and the saint card.

• NO ONE IS SAFE: a meme sticker on the wooden foregrip, left side.
• The S: a white “S” sticker on the left side of the rear sight block. This is not the stamped S on the receiver.
• OSA: our own sticker, on the left side of the receiver.
• LIVE MAG 1: hand-written in white marker on the magazine.
• The saint card: a “Saint Ryan Gosling” meme prayer card, held onto the buttstock with blue translucent tape.
• FRAGILE / HANDLE WITH CARE / THANK YOU: a red parcel label on the right side of the magazine.
• The bullet: a white bullet outline reading EST.2025 on the right side of the receiver.

Which one would you trust behind the counter?

That is the question the video ends on, and we are leaving it to you. What the photos show is the contrast. The HK MR556 A4 carries an illuminated optic, a battery-powered red dot, a laser box and a light. The md.63 carries iron sights, a sling and stickers, and nothing on it takes a battery. Tell us which one you would reach for in the comments on the video.

Specifications

Item	HK MR556 A4 (as shown)	Romanian md.63 (as shown)
Model background	Civilian version of the HK416	Romanian licensed AKM derivative, made mainly at Cugir
Build	Semi-automatic	Semi-automatic, U.S.-made receiver with Romanian md.63 parts
Markings on ours	MR 556 A4, 5.56 mm x 45; Heckler & Koch Inc., Columbus, GA	1987 and a lettered serial on the left; S on the right
Cartridge	5.56×45mm	7.62×39mm
Operating system	Short-stroke gas piston, multi-lug rotating bolt	Long-stroke gas piston, rotating bolt
Receiver	Aluminum alloy	U.S.-made, stamped sheet steel
Sights	1x/4x dual-role optic plus mini red dot	Iron sights
Extras	PEQ-style laser box, weapon light, suppressor	Stickers, leather sling, LIVE MAG 1

On the floor at OSA

Both rifles in the video are store guns we used for the shoot. If the Romanian side of the video is more your speed, these pieces in our case are related:

• Romanian PM md. 63 built from a matching military parts kit: a separate listing of md.63 rifles built on new U.S. receivers with original chrome-lined Romanian barrels. We have not matched it to the sticker gun in the video.
• Arsenal SLR-106U AK pistol in 5.56×45: a Kalashnikov action in the HK’s cartridge.
• HK VP9L 9mm long slide with a Burris FastFire 3: Heckler & Koch, also with a small red dot.
• Norinco Type 56 SKS from Changchun with a 20-round magazine: another Cold War rifle in the md.63’s 7.62×39 cartridge.

For another piece of HK engineering, see how the HK P7M13 squeeze-cocker works.

The grid below updates by itself as pieces come and go.

The short version is on our Instagram. Watch it on Instagram.

General information for collectors, not legal advice. Markings and features describe the two rifles in our photos; check them on any individual rifle. Music in the video: “Sneaky Snitch” by Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0; an excerpt is used.

Sources

• American Rifleman, “New For 2025: H&K MR A4 Series” — https://www.americanrifleman.org/content/new-for-2025-h-k-mr-a4-series/ (MR556 as civilian HK416; 2009 introduction; short-stroke piston, multi-lug bolt; A4 features, M-LOK handguard, 1:7 twist, 1/2×28 thread; aluminum receivers)
• Wikipedia, “AN/PEQ-15” — https://en.wikipedia.org/wiki/AN/PEQ-15 (multi-function infrared target pointer and illuminator; visible laser, IR laser, IR illuminator; in service 2003)
• Cornell LII, “18 U.S. Code § 921 – Definitions” — https://www.law.cornell.edu/uscode/text/18/921 (silencer definition)
• Cornell LII, “26 U.S. Code § 5845 – Definitions” — https://www.law.cornell.edu/uscode/text/26/5845 (any silencer is a firearm under the NFA)
• Wikipedia, “Pistol Mitralieră model 1963/1965” — https://en.wikipedia.org/wiki/PM_md._63 (licensed AKM derivative; 1963; Cugir, Sadu; initially indistinguishable from AKM; mid-1960s foregrip; md.65 first with AKM handguards; receiver year and lettered serial; S, FA, FF; AIM)
• Wikipedia, “AKM” — https://en.wikipedia.org/wiki/AKM (1959 introduction; stamped 1.0 mm receiver vs machined AK-47 receiver; long-stroke gas piston; most widely produced variant; produced locally as the PM md. 63)