Maintaining a Sustained Rate or Fire

Rheinmetall has been awarded a patent (#8225999)for an invention (concept would be a more accurate term) to limit a machine gun’s rate of fire over a period of time.

This M4A1′s gas tube melted after 911 rounds of continuous fire.

All gas operated machine guns fire at a rate which is unsustainable over longer periods of time. The operators need training to ensure that they do not let the gun overheat by firing to many rounds in to short a period of time. This issue received national media attention when it was revealed that M4 Carbine barrels had melted and SAW machine guns had jammed during the Battle of Wanat.

From the Army’s report on the battle

Specialist Bogar fired approximately six hundred rounds at a cyclic rate of fire from his SAW when that weapon became overheated, and eventually jammed the bolt forward. Specialist Stafford noted, “Bogar was still in our hole firing quite a bit. Then Bogar’s SAW jammed. Basically it just got way overheated, because he opened the feed tray cover and I remember him trying to get it open and it just looked like the bolt had welded itself inside the chamber. His barrel was just white hot.”

According to The Ground Precautionary Message ACALA #97-031 (emphasis added)…



The actual rate of fire of an M4 Carbine is 700 – 950 rounds per minute, over 60 times higher than what the gun can tolerate over an extended period of time.

Aside from catastrophic failures, some guns are inaccurate when overheated. The Bundeswehr recently published a report saying that the H&K G36 was useless beyond 200 meters when it was overheated.

Rheinmetall proposes adding a power supply, microcontroller and actuator to machine guns to slow down the rate of fire to keep the sustained rate of fire inside acceptable parameters for the weapon it is installed on. Each time the operator pull the trigger it will fire, but the rate it will cycle is constantly adjusted.

I think this idea has merit but there are some fundamental problems. The foremost problem is that the circumstances where a machine gun might be fired continuously is rare and so operators are unlikely to appreciate a heavy electronic device messing with their rate of fire the rest of the time. They will soon figure out how to disable it and at most it will become a heavy paperweight.

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.


  • Charles222

    Well, not sure you’re getting the idea it’d be heavy, or that soldiers are happy to disable devices on their weapons, but this isn’t anything a good gas regulator isn’t capable of.

    Also, Wanat only occurred due to a set of pretty unique circumstances-poor decision-making, a lack of supporting heavy weapons, and a distinct window of vulnerability in that the troops involved were setting up a combat outpost, which is always going to lower your fighting readiness. The only other time I can think of in the last three decades where a similar situation involved US troops was the Battle Of The Black Sea, which featured a similar collusion of bad circumstances. Twice in thirty years isn’t a good reason to be designing your weapons to face similar circumstances, unless you’re just assuming all Western armies are going to just never be able to properly plan. :p

    • W

      charles, absolutely.

      wanat was a unique animal. you have to respect how smart and resourceful that taliban are. they employed the correct tactics for waging a guerrilla war against a opponent possessing superior technology and firepower.

      – flooding the field to provide background noise to mask their movement noise.

      – taking out the most casualty producing weapons i.e. M120 mortars, TOW launcher, and rockets.

      – firing from a high vantage point onto enemy forces located at the lower ground

      – using available manpower to acquire a 3-1 advantage over the enemy.

      The Taliban were chased out with aerial support, though the damage had already been done. Indeed, their plan was to overrun the defenders, who held their ground and used their fighting spirit to hold off the attackers long enough for supporting assets. A less disciplined unit would have bought the farm.

      • charles222

        The bottom line to keep Taliban from going after you (in my experience anyway) is company-sized operations. Homey the Taliban don’t play that game. :p

  • JonMac

    This emphasis on sustained and ‘suppressive’ fire is one reason why we haven’t yet seen a caseless service rifle. The G11 could stand c120 rounds sustained before cookoff, around half that of the M16A2. Under today’s (arguably unreasonable) expectations, it’s pretty hard to spec a caseless design that meets perceived needs. As long as we continue to use assault rifles as LMGs and give fire at targets we can’t actually see (as distinct from true suppressive fire), this isn’t likely to change.

  • Safety third

    Video games already have a proper solution, bar or light or somethign that goes from green to red the higher the temperature, or just a simple temperature gauge for the barrel, wouldn’t be a lot of limiting stuff waiting to go wrong just some small addon for the gun.

    “When the light blinks red get the fuck to cover and let your gun cool down, soldier!”

    • Safety third

      In short, a temperature gauge for the barrel so soldiers know when to cease fire and sit on their ass for half a min.

      • Jon

        In short, a gauge that shows yellow indicating that the soldier needs to slow down or else things are going to get a lot worse.

    • mosinman

      my temperature gauge is built in… when the rifle gets too hot to hold, hold fire or find another!

    • charles222

      That’s not really how infantrymen employ weapons at all. It’s not an individual thing; we still have fire commands, employed by the team leader, that are meant to help with this sort of thing.

      If an infantryman is doing it alone, he’s doing it wrong. 😉

  • Elliot

    I think that if I were in battle and needed more firepower to the point that I’m melting my own gun that I would be absolutely pissed at some engineer that thought it was a good idea to build in a governor. What if there’s one bad dude left but your gun seizes up because its too “hot.” I think its the soldier and gunners responsibility to manage their own weapon and not some electronic governor.

    • Nadnerbus

      That was my perspective. A rifle is an extension of the soldier, it should do what he asks of it, when he asks it, until it can’t do it anymore. Gimping it in any way where it might do something he doesn’t expect at an inopportune time is bad juju. If the issue is training, then train them better not to shoot their rifle to failure. If the issue is that you are getting overrun, a governor just screws you that much faster. I just don’t see what problem this solves, except maybe lazy training.

    • Denny

      I feel affinity with this comment. If you look say for example on late technology used on motorcycles, there is similarity; they have novadays built-in all kinds of gadgerty which they did not have before. As a result rider is mere ‘operator’ without much active engagement. You can say that with weapon the life is at stake and that is true; so you can argue is in case of motorcycle. Technology is helpful but only to a point.

  • eichenlaub

    Water cool machine guns, semi auto only rifles and carbines. Oh and training. Let the Taliban melt their barrels.

  • john

    There is the Arm-Tech Gas Trap, La France Twin Tube Gas System, and Ferfrans Rate Reducer that would work better in controlling rate of fire also a long stroke gas piston would help

  • jtan

    why not include modern heat sink technology into the barrels? heat pipes, lightweight fins and a small active under hand guard or barrel shroud seems like a small price to pay for a big increase in sustained rates of fire

    • jtan

      oops.. type – active FAN

      • ragnarok220

        A CPU heatsink on a machine gun…why not check out the Russian solution –
        The Pecheneg machine gun ??

      • Cymond

        Fins are a classic idea. JP Rifles has a nifty aluminum ‘heat dissipator’ that fits under the handguards. However, JP claims the barrel has to be profiled specifically for the dissipator. Aluminum is lightweight and has a very high thermal conductivity. Of course, JP is a specialty company. Military mass production would bring the price down significantly.

        barrel profile details:

      • Denny

        As the preceeding comment says, the Russian Pecheneg solution is worth of look. I belief they use combination of means among them also induced longitudinal air draft similar to that used on Lewis MG. They do not issue a spare barrel with that weapon; actually barrel is not ready field-removable either.

        As for heat sinks, there may be a future there. Not necessarily in models as made by JP. These seem to pass heat onto hangurd by radiation. True, saving barrel, but not ‘saving’ gunner’s hand. Better option may be with an alloy which will act as a long term storage with dissipation period extending pass the firing. It should be also noted that a tight fit between this and barrel will be requird – absolutely no air gap.

    • bbmg

      Certainly seems to make more sense to solve the problem by making the guns heat up less. While essential for safety, cladding the barrel in an insulating hanguard is certainly not an advantage either.

      You could also put the bolt movement to work, the M4 Spectre submachinegun bolt is also a piston that drives air past the barrel to air cooling:

      Not sure how effective this is in practice but it certainly would help.

      Here’s a wacky thought off the top of my head, bolt strikes a piezo element which charges a capacitor, which then drives a cooling fan.

      Yes, more coffee.

    • bbmg

      Here’s another idea, replace the bolt spring with magnets et voila, a linear motor 😀

  • John Doe

    This is not how it works on Call of Duty. /s

  • Bull
  • Nicks87

    Sounds like poor training is more to blame than the design of the weapon systems.

    Trigger happy soldiers need to learn better critical thinking skills so they are not destroying their equipment during battle. I understand that its hard to think about things like round counts and rates of fire while being shot at but when things go wrong the first thing people do is blame the equipment.

    Maybe we need to go back to bolt action rifles just so these guys can learn trigger control and how to take aimed shots from cover instead of trying to do their best Rambo impressions.

    And yes I am a veteran myself so I am allowed to criticize my fellow warriors.

    As for Rheinmetall, they’ve been making some pretty awsome gear ever since before WWII so I have faith that they will figure something out regardless.

  • Leonard

    I agree with those who said that training is the essential aspect here, not equipment. A selective-fire service rifle should be used in “semi” unless you are being overrun or in very close combat and need the firepower that “full-auto” provides.

    MGs need to be fired in short bursts. Way more accurate anyways. And for sustained fire with MGs, you need to change the barrels after a time (I am aware that this isn’t possible on all LMGs).

  • alannon

    Just a note that this would not be heavy; a simple embedded microcontroller package (and doing round-counts would be dead simple) can be as small as 3-4 millimeters on a side, a small solenoid to disengage the fun button, and any of a number of sensor mechanisms to detect the bolt cycling. The main problem I see, honestly, is powering it; and I have to wonder if it would be feasible to glue a couple magnets into the upper and recharge the assembly by induction.

    Given the military’s R&D budget, this could probably be implemented with ease, and would be lighter than the material displaced in the BCG.

    As for utility? It’s great on paper…but I’ve been bit on the ass so many times by brilliant plans that don’t work in practice that I’d rather see some in-the-field evaluations before making any broad decision. For instance, if it kept a total round count, I can totally see bean-counters wanting to track the expenditure of every bullet. “Private Pile, why did you fire almost 800 rounds when the unit average was 750?”

    • charles222

      NATO is working on a powered picatinny rail that’s been covered here.

  • Distiller

    Training and coordination. If there’s such a target-rich environment that sustained fire is needed over tens of minutes then someone better call in artillery support fast! Suppressive fire isn’t for sitting in a sandbag castle and pulling the trigger till the barrel melts, it’s for enabling some folks to do something offensive outside.

  • gunslinger

    as an electrical engineer, i think this is cool. but in a practical sense…not so much.

    the more you add, the larger the chance to screw up. i doubt soldiers would want some cmputer to tel them when they can/can’t fire. then, what about “firmware” upgrades and such… now the hackers can attack guns. oh noes.

    so i guess i agree with the “train better” people.

  • Brick

    “Aside from catastrophic failures, some guns are inaccurate when overheated. The Bundeswehr recently published a report saying that the H&K G36 was useless beyond 200 meters when it was overheated.”

    I have to disagree there. All guns are inaccurate when overheated. The bullets will get little to no spin by the rifling, causing an unstable flight. The bullet will not seal the barrel properly anymore, causing less energy and therefore less innitial velocity and therefore a different flight path. This is NOT something new. Heat will cause the barrel to expand. The ONLY solution is to not let the weapon overheat. There is nothing, that can be done about the barrel getting hot, therefore even the first aircooled MGs had a changeable barrel. Reducing the chance of overheating. Every MG 42/ MG 3 gunner (Rheinmetalls MG) has a second barrel with him or on the second man. The SAW also has a quick change barrel. I don not understand, why this specialist did not switch barrels. Even if the gun were still accurate, when the barrel was supposedly glowing white, there is no way the gunner can aim propperly. The heat would reduce what he sees while “aiming” to something like this:

    Lets pretend, that he did NOT heat the barrel over 2370 °F, which is the temperature needed for white glowing steel. This would have directly endangered him and anyone near him. The barrel would have deformed; the material itself would have changed even after cooling ( corngrowth, hardening if cooled in water). Lets just say that he heated the barrel to 1150 °F. This would have caused a expansion of the barrel -depending on alloy – of 0,7 % up to over 1 %. Even this temperature would have therefore caused the barrel to not seal anymore and would have reduced spin.

    So since the solution for a machinegunner is actually really simple, as in he only has to change the barrel, this can be done within seconds on any modern MG; I think that this patent is for weapon stations only. On a remote controlled weapon station one cannot switch barrels. In this case, the additional weight is also not an issue.

    Also I have a another problem:
    Why in the world are M4s used as machine guns? Same thing seems to happen with G36s. The soldiers seem to be firing even though they have absolutely no clue as to where the fire is coming from. Burning through the ammo. Are the soldiers damaging their own weapons (“melting barrels”) even though they do not even know what they are shooting at?

    • Raven

      G36s have a noted issue with the trunnion starting to warp when used for sustained fire. Notice how H&K have completely given up on the G36 and are pushing the 416 now instead? There’s a reason for that.

  • Lew

    A simpler way to improve the heat dissipation is to increase the surface area of the barrel. Flanges etc are very succesful at doing this, though they tend to increase the cost of the firearm it might be worth it in the long run (as barrels tend to last longer).
    In the case of Wanat so many things went wrong I’m not sure anything could have helped very much. A machinegunner who doesn’t change barrels is doing something wrong, a rifleman who uses his rifle as a hose is also doing something wrong. That being said I can’t help but thinking that DI and the M4-profile barrel made the situation worse.

    • Tim

      I seem to recall Mr. Browning had a rather elegant solution for overheating machine gun barrels.

  • Reg

    The total weight, battery, electronics & solenoid for this would be about as much as a single round of ammo. Anything more than that would be embarrassingly poor engineering. The solenoid need only trip the disconnector. Very low power requirement and failure mode is do nothing which is current behavior.

    Whether it’s a good idea is debatable. It certainly would not be difficult to defeat, just remove the battery. The biggest issue would be remembering to check the battery every few months to make sure it was still working.

    There have been many mechanical rate reducers. There’s even been a PDW designed to fire full auto single handed that used an electronic system to control rate of fire at a rate which produced the smallest dispersion.

    On the M16, burst mode has been available for quite a while. There was a lot of debate about full auto before full auto assault rifles became the norm. The fact that burst mode is not the norm suggests to me that it’s probably not an issue 99.9% of the time.

    On an LMG or MG, one could make a case for limiting sustained fire to skilled user burst lengths so that if someone not well trained on the weapon were using it they’d be reminded by the gun limiting the number of rounds per trigger pull.

    Ultimately, the users will decide whether the idea has merit.

    As for training, there’s a piece of film from Hue showing a Marine loading his M16, sticking the barrel over the top of a wall, emptying the magazine and then swapping the magazine. Not only did he not aim, he didn’t even look over the top of the wall (to be fair it was a reach just to get the barrel over the top). The nearby M60 was equally unrestrained. I’m sure this was not what they were trained to do, but they did what they thought best under the circumstances. I’m quite happy I wasn’t there.

  • Mike Knox

    Well here’s a better alternative: Trigger control..

  • Tony

    This is why water-cooled Maxims are still the king of sustained fire

    • charles222

      And kings of being unable to maneuver with your personally assigned weapon.

      • bbmg

        Exactly, with 100 year old technology, but surely with modern materials and techniques something more effective can be made without weighing half a ton. Sure the laws of thermodynamics haven’t changed, but what with heat dissipation being a ubiquitous problem in engineering and technology we’ve come some way from the Maxim.

    • mosinman

      i think for the hell of it we should build a water cooled MG with modern materials and techniques and see how light it can be

    • charles222

      The fact that you’re lugging around gallons of water in addition to a machine gun that’s going to weigh in at a minimum of twenty or so pounds without a water jacket isn’t going to be subverted by modern technology. Regular barrel changing has left the water-cooled silliness in the dust.

      • JMD

        That just means someone needs to invent lighter water. lol

      • mosinman

        true, but then if you get lost you can drink the water lol

  • Brian

    Being a saw gunner I know that it is ingrained in every rifleman from SOI Sustained 85 rounds a minute fired in 3-5 round bursts 4-5 sec pause no barrel change
    Rapid 200 rounds a minute 6-8 round bursts 2-3 sec pause
    cyclic 650-850 continuous burst barrel change every minute
    It is clear there is a lack of understanding what fire superiority is used for to suppress the enemy in order to maneuver and destroy them. If internal fire cant accomplish this that is what CAS and Call for Fire are for. we seem to be using gear to replace training we all know to well gear fails. maybe they need to go in the quad and do some more barrel changes. haha and I just got the M27 not impressed at all.

    Keep Attacking

    • W

      as a SAW gunner, im sure the M27’s lack of a quick change barrel, closed bolt, and 30 round US GI magazines impress the shit out of you 😀

      • SPC Fish

        im glad the Army hasnt tried to take away our SAWs yet. it is a great weapon system. i would prefer the lighter weight MK48 or whatever the eals call it but a 249 with a para barrel does a pretty damn good job

      • charles222

        When I had a SAW back in the olden days of 2004, we either didn’t bring spare barrels, or only brought along one; weight-saver. We also didn’t really carry enough ammo per man to warrant it; a basic load at A Co 2-22 INF was 600 rounds.

      • mosinman

        yeah i never understood the concept behind the m27 either, unless you want a high end AR. i think its not very useful as an automatic weapon. ive heard alot of gunners like its accuracy, but then it should just be a DMR imo

      • W

        There is also Knights LMG, which weighs a impressive 10 lbs, is compact, belt-fed, and open bolt.

        Replacing a belt-fed, quick change barrel, open bolt weapon with a closed bolt, fixed barrel, and magazine fed weapon is utterly stupid. What makes this even worse is the USMC doesn’t even allow the M27’s superior factory magazines to be used.

      • JMD

        In response to a variety of comments….

        The M27 is not a replacement for the M249, it isn’t meant to be, and it never will be. It’s a “supplement”. It was the USMC’s work-around for acquiring M416s, and the IAR trials were the dog and pony show required to slash through the red tape and get them. They never really wanted to find the best IAR, they just wanted M416s.

      • W

        I dont think anybody said that it will completely replace the M249, though i think it was a mistaken impression over text.

        You’re right, JMD, the M27 is not intended to completely replace the M249, though a few thousand M249s will be replaced (undoubtedly the worn out ones). It was intended as a automatic rifle to enhance the speed of the Automatic Rifleman, who might be otherwise encumbered by the M249. I think a better option could have been pursued.

        Im really not sure about the Marine Corps acquiring the HK 416. I think it was stupid of them to adopt the M27 when there’s no guarantee that the 416 will be adopted for service (unless they know something nobody else knows like what you said).

  • W

    technology is not a substitute for superior discipline and order. Rate of fire and marksmanship is a aspect of these invaluable attributes. There may be extraordinary circumstances where a infantryman is required to push his weapon beyond its mechanical limitations (such as Wanat), and he shouldnt be hindered by a technological devise that will only impede his ability to kill the enemy.

    Barrels cannot get white hot. They will destroy themselves before they get to that point.

    All firearms become uselessly inaccurate and unreliable when they are overheated. Inaccurate at hand grenade range, however, is a moot point when you need to kill the enemy instantly at that moment.

    The Battle of Wanat was a bucket of cold water in the face of the Army and our government. It is my opinion that our “fearless leaders” underestimated the resourcefulness and tenacity of experienced guerrillas equipped with little more than RPGs, mortars and small arms. Our soldiers fought admirably, despite the sheer incompetence and hubris of their leadership.

    • Lance

      W is right on. The M-4 was NOT at fault for Wanat but poor training and the fact no support fire was given to solder at the check point there. Overall this may help in war games and state side test but may not work well in combat.

      Overall the heavier M-4A1 barrel and maybe a heavier SAW barrel is needed.

      • W

        Im not going to blame “poor training” for wanat. Without supporting heavy weapons, those soldiers’ small arms didn’t have a choice but to be shot out. Like I have said before, I would rather have a seized up M4 and retreating enemy than Taliban running around the COP with a functional M4 laying over my dead body.

        If it has up to me, every M4 in the US military’s inventory would have a heavy buffer, SOPMOD bolt upgrade kit (Fail Zero coated bolt and carrier), and heavy barrel (preferably one similar to Noveske’s M249-standard chrome lined barrel). Also issue bottles of SLIP2000 to completely replace CLP. Those features would make the M4 extremely reliable at a comparatively inexpensive cost.

        We can only dream while big army fiddles and overreacts to underwhelming, non-apocalyptic budget cuts. Combat effectiveness and efficiency be damned!

    • Daniel

      I read a report on Wanat that indicated that the lack of fire support was due to enemy action, not lack of support or planning. In short, one of the opening actions of the enemy at the start of the battle was to RPG the support motar positions from higher ground, temporarily depriving the ISAF of its immediate support weapons, and it took a while to get replacement fire support into range.

      Problem with such warfare is that the enemy always has the initiative, you can only react to it. And the enemy isn’t stupid. They know where your support weapons are, and they know enough to turn it into scrap metal the first chance they get.

  • hikerguy

    Seems a rather complicated device to add to keep rate of fire down. Wouldn’t the FERFRAN rate reducer be more practical? How about just training them to shoot correctly?

  • Denny

    Perhaps revealing but not that new information. But it is good to hear and to know capacities of soldier fired small arms with definite certainety. This convincing argument can be only done by test of fire. I think, we can eventually bravely state that rifle/carbine (even with full auto capability) is not suited for machinegun role or anything close to it.

    This also touches of issue of tactics. Today’s battlefield scheme is not the same as in World War one. Then, the Maxim or Spandau were the king. Today, you will fight small moving groups of enemy engaging in faster pace. One conclusion might be that full-auto is still usefull, but it ought to be limited to very short bursts. And this is probably not false presumtion since those couple extra shots may add to hit probability.

    I enjoy reading other participants notes; this is usefull think-tank.

  • Jacob

    With variations in temperature, daytime versus night time etc, rain, snow etc. Trained standard numbers aren’t necessarily going to produce optimal results. Something that could provide you with the ability to identify and sustain an absolute maximum sustained rate of fire in any condition without failure would be an obvious advantage. But you probably wouldn’t want it to directly control the rate of fire.

    If they wanted to it could basically be pinky nail size or smaller. If you wanted something that reported just temperature green/yellow/red you could probably do it in your garage pencil sized. 2in wide x0.25in high x 2in long you could do that and have it wireless transmit the information and post it on facebook, do your math homework and plan your drive from New Jersey to San Diego.

  • Martin M

    You know, this all reminds me of the mindset behind the Springfield 1892 Kraig-Jørgensen. I’m sure you all know the story, but for the sake of others the idea was by creating a rifle that was overly complex and slow to load, ammunition would be conserved and fire discipline would win the day. Of course, contact with the enemy in the Spanish-American war blew that theory straight to…
    The idea of limiting a soldier’s rate of fire in order to preserve the weapon usually results in dead soldiers (and not of the enemy type!). This idea is stupid! I could cite example after example where it was required to bypass safety protocols and disregard the integrity of the equipment in order to win the day.
    We had a saying in SAC. “Make a [weapon] so simple that a fool could use it, and only a fool will.”

    • Agreed. What’s more expensive? A ruined barrel and busted gas tube, or ruined/busted soldiers?

  • I think it’s a pretty stupid idea – too complex for practical application.
    But. . . if you are going to go that far, and it’s the heat that’s the problem, why not put a temperature sensor on the barrel, and have the box adjust the rate of fire based on the actual barrel temperature?

    Sort of an interesting engineering project. Perhaps not much use beyond that.

  • We are trying to solve a training issue with hardware. There are times in combat when burning up a barrel is the correct answer. Also the amount of fire superiority of ripping through a full 200 round belt is necessary and the operator should be responsible for the rate of fire.

  • Kempy

    Finally! We need more computer assistance in firearms! Just like in driving cars, the weakest link in the system is the human. We need guns that know when to fire just like we need cars that drive themselves. What human could maintain a constant rate of fire of 15 shots per minute? That would mean pulling the trigger every 4 seconds. Who would want to do that? Just poke the gun around the corner and let it do the work. I hope they get this up and running very soon.

  • JamesD

    911 rounds huh?

    911 divided by 30 rounds per magazine = 31 magazines.

    I think a soldier would be more worried about running out of ammo if they were firing through that many magazines that fast. Not only that, if a soldier were having to fire that many rounds that fast, they have a bigger problem and limiting their rate of fire will just get them killed anyway.

  • bbmg

    This is a commercially available item:

    Not exactly a new idea:

    Modern extrusion techniques can make pretty complex shapes:

    Surely an effective barrel hear dissipator can be made that doesn’t add much weight to the rifle.

    • bbmg

      Probably written by the marketing department for the Lewis at the time but this is worth the read:

      COOLING SYSTEM.—The method of cooling employed in this gun is as simple in principle as it is effective in practice. No moving parts are employed. Closely fitting the steel barrel is a cylindrical jacket of aluminium having deeply cut longitudinal grooves throughout its length and circumference. Over this aluminium jacket there is a thin tubular steel casing, the muzzle end of which extends at reduced diameter beyond the end of the jacket and barrel. The jacket and tubular casing together with the barrel mouthpiece constitute the entire cooling system. The specially shaped barrel mouthpiece screwed to the end of the barrel serves the double purpose of firmly securing the radiator in place and of so directing the powder blast at each discharge as to greatly increase the “ejector action” of this blast in sucking cool air from in rear through the longitudinal grooves (air passages) of the radiator. The tubular steel casing serves to confine the blast of cool air within the course of the air passages and hence in contact with the aluminium of the radiator. The high specific heat, the great heat conductivity, and the low specific gravity of aluminium, combined with an exceedingly simple and durable construction, produce a cooling system for the gun that is at once practical and efficient, without rendering it too heavy or bulky for general field service. No extra barrel is carried on the firing line, and water is never needed for cooling purposes.

      VELOCITY.—Another useful effect incident to the cooling system is the increase of velocity, due to prolonging the gas pressure upon the bullet after the latter has left the muzzle. This increase of muzzle velocity is more than sufficient to compensate for the loss of the slight amount of gas energy required to operate the gun mechanism, and it is found in practice that the gun gives a slightly greater velocity to the bullet than can be obtained from the same length of barrel in a shoulder arm firing the same ammunition.

  • Tom

    These M4, M4A1 video’s are no longer online.. But i have seen them when they were first published.

  • Raffaele

    Hi to Alls from Italy
    and mount “heavy barrels” in/to the rifle?

  • Ian

    Some of the Marine’s IAR candidates drastically increased the sustained firing rate into the 30s easily. They even passed a 600 round magazine dump. Since the IAR trials were a facade for the HK416 acquisition program though, the public probably won’t ever know about them.

  • Brian

    I am a former saw gunner and was given the IAR. Our company currently has 6 m249’s and 27 IAR’s the saw are in the HQ PLT suit and are not issued to any one. The marine corps and its intent was maybe to augment but it obviously is trying to replace our fire team and squad internal fires with the IAR because of the current conflicts marines find themselves in. People paid more than me feel we don’t require the type of fire power that a m249 provides also money saved due to no more belted ammo or less acquisition. If we get called into a more conventional war zone we will certainly see the SAW returning to the fire team and squads. As long as we are fighting in a block 1 and 2 area we simply do not require that type fire power even if we want it. To address the IAR it is light but currently I have to carry 22 30rd mags because we have a weapons system with no approved high capacity mags. and for the SAW A majority of the unreliability reported with the saw is from shooter error its a wonderful weapon that if improved upon would be a HAUS.