The FN SCAR IAR has been rebranded as the FN Heat Adaptive Modular Rifle (HAMR). This automatic rifle includes the clever IAR feature of firing from a closed bolt (increase accuracy) until it heats up to a certain temperature and transitions to a open bolt configuration (better air flow and cooling).


From the press release …

Derived from the innovative FN SCAR™ weapon system, the new FN HAMR is a revolutionary, lightweight, magazine-fed, 5.56x45mm infantry weapon that enhances the automatic rifleman’s maneuverability and displacement speed while still providing the ability to suppress or destroy both area targets and point targets in today’s fluid battle space. In addition, the visual profile and the firing signature of the FN HAMR are virtually identical to that of the standard infantry rifle, thus reducing the counter-fire threat from enemy forces.

The high-tech FN HAMR platform is a unique, highly adaptable, fully-modular selective fire weapon system that bridges the gap between an individual battle rifle and a squad automatic light machine gun in one compact package. For enhanced accuracy and greater first-round reliability, the magazine-fed FN HAMR initially fires from the closed bolt in either semi-automatic or full-automatic modes. For added safety during sustained fire situations, the FN HAMR automatically transitions into open-bolt operation in both semi-automatic and full-automatic modes before reaching the cook-off temperature of the chambered cartridge. Once the chamber temperature has dropped to a safe level, the FN HAMR automatically transitions back to closed-bolt mode. These transitions between closed-bolt and open-bolt modes are thermally regulated by the FN HAMR and occur without any manual intervention by the operator.


The rifle weights 11.2 lbs (Including Grip Pod) and has a 650 rpm firing rate. FN claim 1 MOA accuracy when firing from a closed bolt. The company only announced a 5.56mm NATO version (same as IAR).

Defense Review has also written about the HAMR.


Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • B & norm, thanks for the correction.

  • What is the lenght of barel on HAMR/IAR? Looks little longer then on standard SCAR-L.

  • Doug

    Wow, that is awesome. I am quite impressed.

  • SpanishInquisition

    Seems to be a truly original and innovative product. But like the IAR, still needs something better than the standard 30 rnd magazines.

    MC HAMR ? there is also a “DJ CHEAPSHOT” 😉

  • Phil Ward

    I must congratulate you on the second pic, that’s made my afternoon 🙂

  • [Insert crude Captain Hammer joke here]

  • sean


    Didnt Leupold just release their ACOG killer called the HAMR?

    Cute acronym FN, but you were beaten to the punch.

  • yamalink

    The price is too much which means I can’t touch this….(insert music that will stay in your head all day)

  • sadlerbw

    I have to admit, a temp-controlled switch between open and closed bolt firing is a very interesting idea, and is probably one of the few times that the word ‘innovative’ is really deserved.

  • singleactionguy

    “you can’t touch this. da na na na…” sorry, couldn’t resist

  • LJK

    Anyone have more info on how that closed bolt -> open bolt transition thingy works?

  • R N

    Can someone explain how this thing works?

  • Greg

    [Slides across the room in his parachute pants]

    “Can’t touch this!”

  • Jim

    Why do they think HAMR will sell better than SCAR?

  • Brian

    Stop… Hammer Time!!!

  • John C.

    Look at the barrel profile in the second pic… now thats what you need in an IAR. How does it know to switch to open bolt? If its a battery run type thing then thats not gonna go well in the military

  • Zach

    The military just loves making “cool” sounding backronyms, don’t they?

    Does anyone know how the open-to-closed bolt system works? Seems like it’d be complicated.

    • I think the open/close transition happens when a piece of metal sitting above the chamber expands with the heat, triggering a mechanism.

  • Vitor

    Quite cool concept! By the way, how it works? Some spring that expands and opens the bolt after a certain temperature?

  • charles222

    The HAMR’s been listed on FN’s website for awhile now.

    This plus the fifty-round Magpul quad-mag has some interesting possibilities, if you ditch that grippod anyway.

  • PRP

    Esta arma não vale nada, é um lixo, bom mesmo é o FAL matador.

  • Jerry in Detroit

    It’s an interesting idea but couldn’t this be better handled through the selector lever; I.e. semi-auto is closed bolt. Full auto is open bolt.

  • greasyjohn

    So I guess once SOCOM didn’t want the SCAR, FN just said “Stop! It’s HAMRtime!”

  • Redchrome

    I just realized I posted to the ancient thread over at http://www.thefirearmblog.com/blog/2008/12/23/fn-iar/

    I’m with Jerry in Detroit here. Why not do semi-auto from the closed bolt and full-auto from the open bolt just like the FG42 did? I can kind of forsee cook-off problems with lots of semi-auto fire; or going full-auto for a while and then back to semi-auto; but introducing a doodad that’s bound to be fragile seems like a solution in search of a problem when compared to the trouble it’s likely to cause. Hopefully it’s designed to fail gracefully when the doodad breaks; instead of jamming up the works.

  • SamsMyName

    Why not the new Stoner LMG/SAW??

    • SamsMyName, this is an automatic rifle, not a light machine gun.

  • Martin (M)

    I, too, see this ‘feature’ as an item that will be very prone to failure and frustration.

    Back in my nuclear days we had a saying, “Make a weapon so simple even a fool can use it, and only a fool will.”

    The full/open, semi/closed bolt system would be a better scheme. No gimmicks to gum up the works. There’s still the opportunity for a cook-off, but that there will always be such an opportunity regardless of the system. You still have to train and educate, so ultimately it’s a moot point.

  • John

    I dont get it.
    Wasn’t this the plan for the SCAR IAR all along (with the closed/open transition).

    Whats new besides for the name?


  • Rijoenpial

    Hi guys…

    Well, I like the HAMR a lot, and I love the innovative concept of open-bolt/closed-bolt switch…

    They said it is an electronic device on the lower barrel section where the lower rail is that will enable the transition… I would think a mere piece of hardware that would expand with excessive heat would do the trick in activating the open-bolt… I guess we will have to wait and see…

    The HAMR is for military use only…I mean, a full-auto rifle such as the IAR will only be usable by military and law Enforcement agencies… The rest of us will have to just watch the parade go by…

    I think the HAMR (‘Hammer’…now I got it! LOL) should have won the IAR competition, and I truly believe that the only reason the HK416 IAR won was because of lobbying… Even the LWRC IAR was a better product than this HK crap…I guess it is true what they say ‘The weapon chosen was proposed by the lowest bidder’… Even though HK is known for being expensive!

    And wouldn’t you know, even the Germans rejected the HK 417 Sniper Rifle because it’s inaccurate!! LOL

    I guess the Germans aren’t biased towards the gear built in their own country! LOL

    I think the US would learn a thing or two from the Germans!


  • SpanishInquisition

    It seems that the loser design of the IAR competition, the Colt IAR, has been sold to Mexico:


    Mexican marines are putting to good use the Colt IAR with 100 round c-mags against the drug cartels.

    • SpanishInquisition, very interesting. Thanks for the link.

  • iroquois pliskin

    for the curious, here is a video made by fnh usa who’s show the “famous” HAMR (at 1:41) : http://www.youtube.com/watch?v=hc8gKerzUFk

    • iroquois, thanks for the video.

  • Vitor


    I remember reading the experience of someone who tested the IAR guns. He said the SCAR was good, but soldies disliked it reciprocating charging handle. And the HK was the most accurate one, you cant judge the HK416 as an IAR tested by american troops based on how german troops tested the HK417 as a DMR.

  • charles222

    The LWRC IAR completely failed during the 40-k torture test. So no, it’s not better.

    I’d be willing to bet that the HK won because of three key points:

    -Familiarity. The controls and general operation are the same as the M16/M4)

    -Simplicity. No mechanical switching between open & closed-bolt operation; even the FG42 method requires additional parts, obviously)

    -Accuracy. It has been said in this forum and others that the HK416 proved itself to be considerably more accurate than the competing designs. The IAR is clearly weighted towards having full-automatic fire as an emergency option, and also designed with more wars like Iraq in the future, where precision engagement of difficult-to-identify insurgents is vastly more prevalent than the Russian-fighting the SAW was designed for. In my three deployments, I’ve often felt the SAW to be entirely the wrong weapon-it’s not capable of precision fire, it’s extremely slow to take off condition “amber” to engage, and it’s bulky and heavy even with the collapsing buttstock and short barrel. Furthermore, a 5.56mm belt-fed weapon might be devastating against enemy dismounts, but it’s fundamentally useless against, say, a car bomb. You could kill the driver, but getting a mobility kill is a distinct uncertainty; the M240B and M2HB are far, far better in that role of machine-gun use.

    The HK design deals with all of the above issues at the expense of firepower; firepower that has not proven itself to be very useful.

  • doug

    Posted by John C. “If its a battery run type thing then thats not gonna go well in the military”


    Perhaps this has already been experimented with, but what about using the moving piston to help create some sort of power source by using the forces already at work within the rifle?

    That concept sounds do-able, but I’m not the one to know how to put it into action. Perhaps if someone will give me a SCAR to play with, I could come a little closer to putting this into fruition:)

  • William C.

    Rijoenpial, the HAMR/Mk.16 may have been the better IAR, but from what I have seen the HK416 is still a fine weapon. What made the HK416 win in my opinion was the desire not for an “infantry automatic rifle” but for a new carbine. The M27 IAR may have simply been a method to get around the red tape.

  • X-Man

    I just want to correct a comment I have already seen in the past.

    Having an open bolt does not help cooling the barrel and does not generate an air flow through the barrel (unless the gun in an aircraft).

    Otherwise, this blog is my favorite on and I am visiting it frequently.

    HK submission was not the lowest bidder. FN and HK were approx. at the same price, Colt was significantly cheaper.

  • mang

    ‘greasyjohnon 27 Oct 2010 at 9:47 am link comment

    So I guess once SOCOM didn’t want the SCAR, FN just said “Stop! It’s HAMRtime!”’


  • Mike

    You mean this firepower,

    Watch for the drums a little bit in the video,

    The Cl-Mag was developed with FN input, They are located 2 hours from each other, the SAW-MAG is the final iteration of this work.

  • Rijoenpial

    Hi guys…

    First of all, let me address the most used and ridiculous excuse for not liking the SCAR: the RECIPROCATING CHARGING HANDLE! Really?!?! I mean, the AK has one, and nobody complains a damn thing about it! The RCH was demanded by the SOF guys,and there already are replacement CHs, so if they are gonna make excuses, they better have new and much better ones! If you tell me the gun’s electronic device failed during testing, or the gun underperformed, those are credible excuses! The RCH is getting old and never was convincing AT ALL! If an army fails a gun for something stupid like this, then no wonder they have the HK IAR! An AR-15 with a piston! I would much rather have an AR-18 with a piston from the ground up! Don’t get me wrong, I like HK, but ya gotta admit the RCH excuse is very lame! And a SIDE-SWITCHABLE RCH, no less!

    Moving forward, the 416 AR and the 417 DMR are indeed different weapon systems for different purposes, but they are BOTH still done by HK…The high standards do apply for each and every weapon they do! So, if the Sniper version of the 417 fails in what is the most primary function of a SR (ACCURACY), then you can’t help but become suspicious that there is more to this than meets the eye!

    I also do agree with William C. : the HK 416 choice smells and looks like a way to include back the 416 the delta boys loved so much and avoid the red tape attached to a new general weapon procurement program… I mean, with an HK 416 model already in the inventory, they can sell it so much easier to the procurement officials…

    I concede the floor regarding the LWRC’s failure at torture tests… Did not know that! Nevertheless, the HK 416 IAR is a mystery to me still: can’t seem to find any vids of it functioning (we have seen the FNH HAMR in action, we have seen the LWRC in action, but the HK is a blur!)

    By the way, here’s a better demo of the FNH HAMR with the 150-round CL MAG from ARMATAC, iroquois pliskin:



  • Rijoenpial

    OH, sorry, almost forgot:

    the switch between the open-bolt and closed-bolt can also be made MANUALLY:


    The automatic switch is just an innovative security precaution to avoid cook-off rounds!

  • Action Saxon


    You obviously have not fired the weapons in question. The “RCH” is only one of the issues that we (the testers) did not like. It was the one thing universally disliked by all. It is both higher on the receiver and of a longer stroke than the AK. The second thing is the stock. The cheek weld area is awkward and tends to move downward in successive shots. The general ergonomics where designed by somebody who went to school for ergonomics but has never carried, used or fought with a rifle. The 416 points very naturally and stays there. That alone won the day, especially given the rest of the testing. In general, an opinion is only worth the experience behind it.

  • Rijoenpial

    Action Saxon,

    I said multiple times that the RCH was not imposed by FNH but rather a specification emanated from USSOCOM… The weapon was submitted to 4 Management reviews, with 4 prototypes of the SCAR being produced, so I think these probs would have been pointed out and sorted during that time…

    If the RCH was that ‘universally’ failed by testers, it would surely have been replaced/perfected… So, Action, if you were part of the SOF testers during the 4 Management Reviews and so on and so forth, I am sure your ops would have mattered, especially being a ‘universal’ issue among testers…

    …And the RCH was never replaced or changed from Prototype 1 to Prototype 4…!

    So, I ask you, assuming that from prototype 1 to prototype 4, the RCH has been maintained virtually unchangeable, contrary to the folding stock, which evolved slightly from P1 to P4, what are the odds of the RCH being so criticized and nobody doing anything about it?…

    Also, you bringing up the 416 clearly illustrates this: the 416 is merely a piston AR-15, so it is a patched up AR-15… In a word, its the M4 but with a piston instead of a DI gas tube! I am not surprised M4 people liking the 416, being the same design and all! AND the Hk416 is German, and it says so on the magazine well!

    I am not opposing your testing here, Action Saxon, but I should popint out that experiences DO vary regarding the SCAR from user to user: I have heard of many people liking it, mostly civilians, especially mentioning the ergonomics, the low recoil, etc…

    Again, as I asked before, if the RCH and cheek weld are so bad as you say they are, why did the SOCOM buy the Mk17 anyway, which has the same design, same RCH, virtually the same system, the same cheek weld area, with only a different caliber?

    That is why your opinions aren’t convincing to me, Action… If what you say is true, then it wouldn’t make sense the long and arduous 4 prototype design, tweeks and test stages, which were heavily tested by SOCOM, keeping the RCH and the cheek weld area practically unchanged, and the USSOCOM would not have bought the SCAR Mk17, which is exactly the same as the mk16, but in a different caliber…

    So, that dog won’t hunt for me! The ergonomics was heavily tested, the gun was deemed reliable, solid, hence the Milestone C approval just a month before SOCOM switched purchase priorities from the Mk16 to the Mk17!…

    Many people who have shot it liked it… the learning curve is, for a trained pro, child’s play comparing with the one required for the ACR, for instance…

    I am not blind to the RCH being awkward for people not used to it, but between that and the stock, I think that a weapon’s value is primarily based on reliability, accuracy, longevity and low maintenance required, not ridiculous things like that… A trained pro will learn the kinks of a weapon through training, before deploying that weapon…I would be more worried about my weapon jamming than things like comfort or a charging handle going back and forth! I make mine the words of someone who said that the RCH is no more bothersome that the empty shell casings being ejected!

    I have seen the SCAR operate and never saw the cheek weld go down unless it was not properly locked in the first place… Also, the RCH was placed in the same place the ACR’s CH was (high on the receiver and to the front) and nobody has complained about that on the ACR…

    And If I may say so, Action, your ‘ergonomics’ remark is clearly ignoring the fact that the FNH is one of the best and most experienced weapons manufacturers on the planet! The design department that gave us the P90, the F2000 and the Five-seveN, does know what they’re doing! And may I point out that virtually all their weapons, except for the FNC, have non-reciprocating charging handles, so they do know what they’re doing!

    It is somewhat funny you mentioning ergonomics when the M4 has been criticised so often for not having much: no folding stock, the charging handle is in an awkward position, the forward assist is located in a different area of the weapon, making the user have to make 3 movements (magazine placement-charging handle-forward assist, all in three different parts of the weapon, whereas the SCAR only has two, with the RCH also used as forward assist)… so, so much for the ergonomics part of the M4!

    The M4 and the SCAR are separated by 20 years of evolution in materials, weapons design and manufacturing costs! The M4 is a well-oiled machine, manufacturing wise, and has been disseminated in the US and in Americans minds, so that is an advantage the M4 has the SCAR hasn’t! But this is hopefully going to change next year!

    The new replacement for the M4 scheduled for 2011-2012 will either make it or break it, but one thing is for sure, there is a lot of pressure to modernise the assault rifles used by American forces! if the M4 was so good as people say they are, why would they schedule it for next year and worse not having the M4 compete in it?

    I know, the Army has cried WOLF way too many times to be believed, but from what the procurement officials say, this may be the real thing!

    Time will tell!

    I am very long now… My apologies…


  • Action Saxon


    While you may be factually correct in terms of “who said what to whom,” When FNH talks with SOCOM, it comes down to one issue to me. What tool does the worker need? If you work for SOCOM procurement or FNH (or a very narrow selection of other players), the value of your opinion goes up some what. IF you may actually be issued the item and sent to war with it, you get a “full share” in the opinion game. Otherwise your opinion is that of an interested observer. You are actually entitled to voice that opinion all you want! The guys securing that right may be issued the tool in question, so it better do what THEY need. Not what a logistician or congressman needs.

    I do appreciate your point of view and your articulation of it as well. I just find it largely irrelevant.

  • Rijoenpial


    thanks…I guess… LOL

    I like to think that when a weapon like the SCAR is procured and built from the ground up, the FIRST priority is for it to perform and be reliable…

    I can’t fathom the idea of having a weapon being less than a tool for primarily protecting the user, for self-defense purposes! Most people think a weapon is for attack, but actually the first idea behind a gun existing is for self-protection! So, the weapon needs to be made to protect the user in whichever settings and no matter how harsh the conditions on the ground are!

    I am sure both FNH and USSOCOM didn’t do the battery of tests they did on the SCAR if not for securing that self-defense concept! Surely it would not be approved through the various milestones if it was poorly performing in that area!

    Again, I would be shocked and appalled if a weapon was approved through the cracks, through lobbying and other corruptive means, without securing what is the most important function of a weapon in war-like scenarios: to protect the user by flawlessly performing the task it was created to do! Whenever a weapon fails, it negates it’s reason for being, it becomes THE ennemy or, at the very least, the ennemy’s greatest ally!

    So, both the primary and secondary weapon at the soldier’s disposal must perform as flawlessly as humanly possible, and I should add to this, as ‘engineeringly’ possible!

    So, I agree with you on both counts: my opinions are just important to me, as yours are to you, but I think we also agree that the weapon soldiers rely on to survive the battlefield needs to be flawless and reliable! And also time-saving in terms of maintenance! The less time you spend cleaning and lubricating the darned thing, the more time you have to perform other tasks!

    Now, going back on topic, as far as the HAMR is concerned, I don’t know in what criteria the weapon failed, but I sure would like to know… I think all these things that cost the taxpayers millions of their hard-earned dollars, there should be full disclosure regarding the initial costs, the expenditures, the final costs, the estimated costs of the other contestants, etc…

    I usually think that if things were done honestly, there wouldn’t have to be any need for hiding that information or making it purposefully ambiguous or reach the media already filtered out and/or manipulated!

    If things are done by-the-book and on the honesty, integrity side, there is no need to hide the info or deem it classified!

    This IAR affair is full of holes, contradictory statements, flimsy explanations and therefore, not entirely believable just on hear-say!

    I am usually this suspicious in multi-million dollar deals…! LOL


  • Some Guy

    The reason why this probably wasn’t chosen is becuase it’s 11.2 lb and it seems to only fire (5.56mm?) Ammunition.

    It is probably extremely reliable, doesn’t overheat very quickly, and is accurate.

    It’s actually, probably better than the M27 IAR that the marine corp picked…

    But the Marine Corp wanted something LIGHT, which is why 11.2 lb probably didn’t allow it to make the cut. :/

    I wonder if it could be lighter; but that’s probably the barrel and heavier firing system that makes it so much more reliable.

    I think that, if they made this in 7.62mm x 51mm NATO, it could easily replace the BAR position.

  • Arthur

    STOP…. Hammertime!


    HAMR TIME B****S


    what year was it made