Seen at SHOT: HK MR556SD and MR762SD Suppressor

Foreground: HK MR w/FHMB. Background: with BPR in place.

Foreground: HK MR w/FHMB. Background: with BPR in place.

One of the great things about SF is the way you learn a lot of skills. For example, if you went to the old O&I school, you got an excellent and in-depth intensive course in taking first class documentary photographs. We regret that the old teammate who took these photos is not a graduate of that course. In fact, even though he’s now in the industry and was at SHOT, he was our team medic– and a very good one.

At the SHOT Show recently, HK’s new MR556-SD and MR762-SD, which exploit new suppressor technology from Utah-based OSS (Operators Suppressor Systems), caught his eye, and he snagged us a few cellphone shots.

OSS Mission Logo Black

Blurry close-up of the FHMB

Blurry close-up of the FHMB


We haven’t seen anybody else documenting the innards of this new development. So we’re going to do it — even though the photographs we have are less than fantastic. Discussing this new weapon with guys from the days of the old MP5SD, we thought that this might be a good replacement for that weapon, now that everyone uses carbines rather than submachineguns for CQB. The advantages of suppressors are pretty significant in combat.

We were less than shocked to discover the guys at OSS came out of SF and the Ranger Regiment, inter alia. 

Here’s a look down the throat of the thing, we believe this is towards the muzzle end:


We take this to be the breech end of a BPR backpressure regulator component.

Here’s another interior shot:

We think this is the inside of the BPR.

We think this is the inside of the BPR.

Here’s a blurry look at the outside:

This appears to be the outside of a BPR-2

This appears to be the outside of a BPR, perhaps from its length the BPR-2

The nomenclature of the components of this suppressor will be clear enough, below.

What you’re Seeing in the Photos

The OSS suppressor has several unique design features:

  • This is the BPR-1. The BPR-2 is similar but longer.

    This is the BPR-1. The BPR-2 is similar but longer.

    Its exterior is octagonal, not round. (HK installs a rail to match on the SD versions). The octagonal rail spreads the rising heat to reduce mirage effect.

  • It’s modular. (That’s the big buzzword of SHOT 14, isn’t it?). Part of this modularity is: it’s caliber convertible between 5.56 and 7.62 (or, presumably, other calibers). They also make a big-daddy that’s convertible from .300WM to .338LM.
  • It’s self-tightening (can’t shoot itself loose), but can be removed by hand.
  • The gas is turned back by a deflector, and then makes its way through the unit, gradually expanding, before being vented back towards the front of the suppressor and vented to the air.
  • This is the BPR-1. The BPR-2 is similar but longer.

    This is the BPR-1. The BPR-2 is similar but longer.

    The typical OSS suppressor has three components, the first is a Back Pressure Regulator which is available in two variations, BPR 1 actually fits back over the barrel and reverses gas flow (like a car muffler) and shortens length, and BPR2 mostly extends past the muzzle. The second is the Signature Reduction Module (SRM) which attaches to the nose of the BPR. The third component is the custom Flash Hider Muzzle Brake that is used to mount the BPR. The BPR can be run without the SRM — alone or with a standoff/flash hider device, but if one purchases the BPR and SRM at the same time, it’s a single serial number and single tax stamp.

  • Pricing for the OSS suppressor on its own is quite reasonable. At the SHOT Show they were quoting ~$1500, but it’s not clear what HK will charge for the SD … yet. They do offer the OSS FHMB as standard on the new MR556 Competition Rifle at an MSRP of $2,947, so you’re looking at about $4,500 to have the equivalent of the SD. Will the factory SD command a premium, or sell for a discount?
  • Flash Hider/Muzzle Brake / QD attachment for the BPR

    Flash Hider/Muzzle Brake / QD attachment for the BPR

    They guarantee a 10,500 round life cycle for low rate fire if you follow their maintenance schedule. This is, to be blunt, unique in the industry. High rate fire? If you’re firing 3-5 round bursts at 850 rpm (typical for a piston AR like the HK416/MR556) you’ll see sound reduction degrade after 4,500 rounds. It’s user and armorer serviceable; the one wear part goes for $40, isn’t the NFA serialized part, and resets your wear to effective zero.

  • They do not increase back pressure in the system. Again, unheard of. How did they do this? Well, part of the secret sauce is that they didn’t go for sound reduction to the point of interfering with weapons function.  They went for -26dB (ear safe) rather than stretch for over 30 and run into reliability and maintainability issues.
Standoff Device and FH (optional)

Standoff Device and FH (optional)

So there is a tradeoff in going with the OSS suppressor. That tradeoff is biased towards benefits for the user that shoots a lot and cares more about tactical suppression than absolute stealth (OSS was founded by SF / SOF guys). After all, if you’re absolute-stealthin’ it, you’re probably not doing magdumps from an AR platform. If you’re mag-dumping with extant suppressors, including some quite decent ones like the issue KAC SOPMOD user or the AAC, you not only generate a lot of back pressure, you risk baffle strikes as the thing heats up. Those suppressors are built well enough to survive the baffle strikes, but what happens to accuracy is not good.

They explain the octagonal barrel quite logically:

The OSS Advantage is based on patented design technology that effectively manages heat & sound reduction while regulating back pressure on the weapon’s firing system. The octagonal external heat shield redirects the heat away from the top center-line of the barrel to a wider point, which moves the mirage from the center sight line of the optic. Every shooter appreciates a sight picture that is not blurry. 

This is typical of the way the system is thought out with the end-user in mind. If you’ve used a suppressor like the decent Knight’s Armament Company unit on SOPMOD 1 guns, you’ve found the muzzle-heaviness and increased length forward at least a mild irritation. The BPR1 in particular doesn’t mess with your balance as much as traditional muzzle-attached suppressors do (this is one reason not-everybody runs suppressed all the time). It’s about 6 inches behind the flash hider, and .6 inch in front. But even the BPR2 only adds another inch or so in front. The SRM adds another 4.2 inches in front of the muzzle. The components are light; the BPRs under a pound each. We’ll take five inches and a pound-and-a-half forward to maintain our hearing in and after a firefight.

The HK integral suppressor guns are now catalog items, although the H&K website isn’t there yet. Soldier Systems has scans of the one-pagers on each, which we reproduce below.
MR556A1-SD handoutMR762A1-SD-440x592


Here’s a shot of the cutaway which we snagged off of HKPro, where it seems to have been second hand. Original photographer please let us know so we can credit and link you.

OSS Suppressor Cutaway

For more information:

The OSS Website is great. They give up about as much information they can without the ITAR police landing on ’em with both feet.  They’re also on Facebook for you damned kids.

This thread on HKPro gave me one image and a few facts about pricing of the OSS suppressor.


11 thoughts on “Seen at SHOT: HK MR556SD and MR762SD Suppressor

  1. Skihugger

    Total M4 overload at SHOT made it difficult to weed out the unique items. A bevy of companies trying to reinvent the wheel. This was something that stood out. As always, this is a thorough and well written article.

    1. Hognose Post author

      This was one of the most interesting M4 adaptations. Like the 416 itself, they’re not trying to do anything revolutionary. I thought it was particularly interesting the way they selected a level of suppression and designed to that spec and no more, rather than the more usual “what’s quietest” game which reminds me of the PC megahertz wars of the 90s, or choosing cars based on horsepower (to beat up on another gang of Teutonic engineers than HK for a change, it took BMW decades to figure out that people use a cup holder more frequently than 0.9g on a skidpad, for instance).

  2. Aesop

    So from my world of reading xrays and CTs, they’ve apparently engineered it so the barrel fits inside the suppressor, rather than hanging it on the end, added an indexing/sealing contour beyond the threads, and cocooned the thing back over the barrel but inside the rails to save space on the functional OAL of the can. And just for grins, made it operator-level serviceable, user restoreable, and for sale to the actual public, instead of just to Tier One JSOC Ninjas with .gov credit cards, because Capitalism.

    And, with their see all PR drawings, given a huge leg up to anyone prototyping with, ah, 3D additive manufacturing capabilities and inclinations.

    Farking awesome.

    Next year, post a wish-list, and maybe the Gun Fairy can get you some better snaps and leave them under your pillow. ;)

  3. Bill K

    For the ignoramuses among your readers, of which I include myself, what is the principal role of suppressors in military use? You mention HK’s goal of -26dB as ear-safe. I thought that when practicing, even in the military, everyone wore some other form of ear protection, so a suppressor would become important only in battle, not practice. And I assume that by and large, the soldiers of WWII had no suppressors, but experienced, at least in the cases of the Wehrmacht and Russians, long lengths of deployment and noise assault on the ears, yet seemed still able to function better as seasoned veterans than new fresh-eared recruits. I also know (and won’t get into here) that noise damage to the hair cells of the cochlea is highly frequency dependent – other frequencies are spared.
    So is the main function not so much to spare hearing for posterity as it is to spare hearing of faint noises immediately after firing, e.g. to detect opposing movements?

    1. Hognose Post author

      On use of suppressors in training — been around and around on this with people worried about the logistics. (The suppressors we had, Knight’s Armament Company models, have a finite life. But I’m big on “fight as you train, train as you fight.” For one thing, every suppressor causes some shift in bullet impact. Thing is, that big warehouse where they keep the “go-to-war” stuff? It doesn’t exist, so if you’ve shot your baffles out you’re screwed. We also did not have, pre-9/11, any suppressors at all, and then when they finally came in we did not have one for every man (we had 4 per ODA and ODB, but of course could assign them around). We didn’t get them until after the first Afghan trip. When they came in, they went to Group HQ which was in another State. Group issued them only to the subordinate units in their own State and left our slice in an ISU-90 at Group HQ. We got them, and the SOPMOD II kit, on return, but went to war with SOPMOD I minus suppressors.

      The WWII (and Korean-era and Vietnam) guys mostly wound up deaf. I’m not going to pretend to understand geriatric deafness in toto but I believe the lack of ear pro up to about 1970-something is why so many Vietnam guys are breaking with bad deafness and especially tinnitus issues. As I understand it, exposure factors include loudness, duration, and a kind of overall amount almost like rad exposure. Starting in the 1970s, the Army became a true believer in hearing protection on the range (even though competitive shooters and many soldiers had been doing it beforehand).

      I remember about that time my father and most other non-commercial pilots got headsets for the first time. Prior to that they flew 1- and 2-engine planes using a hand microphone and a speaker in the headliner. Those guys are all deaf as a stick of wood.

      The suppressor is not just for ear pro though — it provides a tactical advantage. Even though they’re not as quiet as Hollywood would have you believe, they do make it much harder to locate your position. That’s a life-giving, death-dealing reality on the battlefield. And they make it possible, in some circumstances, to engage an enemy without him understanding some aspect of the totality of the engagement. To plant confusion in his brain is as good as killing him, practically. Better, if he’s the leader, because if you screw the leader’s situational awareness up the whole unit acts like it’s drunk and you can do what you have to do — whether it’s defeat them in detail, carve one out for a trip to custody (I’m not underestinmating the difficulty of this, it’s the hardest combat mission you get and 90% of them fail), or most often, break contact and continue mission.

      There’s a lot of reasons combat experience tends to accumulate. Some of it is simple statistics (a decade or so ago, some statisticians demonstrated that given attrition and victory rates, the emergence of a few high scoring fighter aces in WWI like the Red Baron was an inevitability, and perhaps not a mark of combat genius. This is a very controversial finding!). Some of it is that adaptation to the environment needs to be rapid or it’s too late. The old expression, “the quick and the dead,” used “quick” in its sense of “alive,” but it works pretty well (and most modern people understand it) as “the (mentally) quick and the dead,” or to put it more academically, “the rapidly-adapting and the doomed.”

      Just like a fighter pilot creeping up behind an enemy warplane, an experienced man or unit in ground combat does not give the novice enemy any chance to develop experience. “Ambush is murder” if you’re doing it right.

      These adaptations can, perhaps, lead to maladaptation to postwar life in some individuals. Remember the WWI essay on “The Repression of War Experience” we linked to some months back? Although it does seem to me that posttraumatic stress is more likely to become traumatic in individuals with low levels of stress inoculation (or realistic, stressful training). If “nobody’s expecting the Spanish Inquistition,” he can’t steel himself for it… but I am not a pshrink, just someone curious about it.

      1. OBob

        “Even though they’re not as quiet as Hollywood would have you believe, they do make it much harder to locate your position. That’s a life-giving, death-dealing reality on the battlefield. And they make it possible, in some circumstances, to engage an enemy without him understanding some aspect of the totality of the engagement.”

        Great point! The first time I worked the pits at basic was the first time I heard the supersonic crack of nearby fire. It was a revelation and I completely understand the natural tendency to turn towards the source of the sound, which is of course 90 degrees to the source of fire.

        Regarding experience, a in a sobering book I recently read on the battle of Britain a flight leader lamented that if he could give a fresh pilot just a 30 minute training flight on combat (and not school house) flying he could greatly increase his survivability, but often lacked the time for even that!

        1. Hognose Post author

          That is one of the big reasons that the known distance (KD) range is good in basic. If guys don’t have that experience of hearing rifle shots “crack” they don’t know when they’re under fire and just stand their like great stupid apes! (Of course, if you survive the experience, it only happens once… next time you react appropriately).

  4. Bill K

    Thanks! And you are right about deafness being similar to rad exposure. There is an XY=C type relationship above a threshold of around 85dB, as follows:
    90 dB = a loud lawn mower, 8 hours continuously can cause hearing damage
    95 dB = NY subway, 15 minutes “” “”
    100 Db = loud shout at 50 feet 1 minute “” “”
    125 Db = painful, shotgun almost certain hearing loss
    And I knew about the bullet shift +/- suppressor, having read that before somewhere.
    But having heard the “suppressors are not silencers” mantra so many times, it is illuminating to read that it truly can make the source of fire harder to locate – I guess I just took it to the logical extreme that suppressors ONLY helped with hearing preservation and essentially nothing else, part of that purpose statement of yours, “A lot of nonsense is written about weapons, especially on the Net.” So now I see why leftist politicians want to ban suppressors – they personally fear the ‘Enemies Foreign & Domestic’ scenario.

  5. Aesop

    Actually, they want to ban them because they go on guns. If they could get the votes, they’d ban slings and holsters too. It isn’t because of functionality, otherwise they wouldn’t be suspending 5 year olds for pointing finger guns at recess. They really have a phobia.

    That there may indeed be some detriment to a someday-militia undoing their jackbooted schemes is merely a happy bit of serendipity.

    1. Hognose Post author

      In Washington DC, they raided a guy because his wife said he had guns (amidst a messy divorce). They didn’t find guns but did find a box of ammo and a box of sabots for muzzleloaders. Informed that that no-warrant raid might wake up the law student in even today’s somnolent judges, they got a warrant on a shaky affidavit and went back AGAIN. This time in the middle of the night with the whole SWAT Team. This time they really scored, finding a dud shotgun shell he’d kept as a souvenir (primer indented, shell not fired).

      They also seized great evidence of wrongdoing: a holster. So you’re not far off.

      DC prosecutor, neo-Nazi Irv Nathan, who didn’t prosecute David Gregory for a similar violation, has been insisting this guy eat a felony and do a year in prison for the shotgun shell. He even sent his slugs in to defend the warrantless raid (the judge did wake up and threw the proceeds of that raid out).

      There was never any gun. Guy leaves his guns at his sister’s house, which is outside of DC in a country called the United States of America.

      The guys leading the raid are called something like the Gun Recovery Team and are heavily resourced. Meanwhile, the DC police closure rate on homicides is for shit, even though very, very few of these are stone whodunits. They don’t need Columbo or Sherlock, they need someone willing to go saddle up and talk to the victim’s associates to see who done ‘im. And they couldn’t be arsed. There are guns to recover, some of whom are owned by political opponents of neo-Nazi Nathan.

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