Air cooled (as opposed to water cooled) heavy, medium and light machine guns use an open bolt mechanism to assist in cooling the barrel/chamber. I am not aware of any water cooled machine guns now in service in the US military. There may be some...but I am not aware of any.

M2 is the military designation for the Browning .50 caliber heavy machine gun...NOT the M2 "Carbine" which is not considered a machine gun, it's a selective fire rifle.

In the military the term "gun" is normally restricted to crew served weapons like machine guns, artillery, mortars, etc.

There are numerous military manuals and civilian books covering machine guns...their design, operation and specs. Perhaps you might want to read some of them to answer all these questions you have on this topic. There used to be an outfit in Las Vegas that held machine gun shoots every year that were open to the general public and you could spend a day learning about and firing automatic weapons. Don't know if they are still around.

Rick

Why do machine guns cook-off rounds? Specifically, the M60, M1919, M240, etc.

Thanks,
ASS_CLOWN

I think the primers ignite from high temperatures. Smokeless powder is far more heat resistant and stable, so the primer is the likely culpret. I am sure there are some spces for primers and their tolerance to heat, but I don't have any.

I think the term cook-off pretty much describes it. Barrels get so hot during sustained fire that the round fires without the trigger being pulled. That is why the barrels can be changed out on many of these weapons.

I've seen M60 barrels glow red during sustained firefights. That's why the A gunner is supposed to carry a second barrel and the asbestos gloves to be worn while changing it.

Isn't M60 fitted with a fixed firing pin as is our mg? I believe it is. And if so the most plausible explanation is that the trigger fails to catch the bolt. Dirt, cold temperature in combiantion with greasy lubricants, too high firing rate (bolt travels too fast), lack of lubrication, faulty trigger unit.



As each round remains in the chamber for a very short period of time, barrel heat is a very unlikely explanation.

"Cook-offs" on MG's that fire from an open bolt occur in the feed tray...not in the chamber. If they happened in the chamber how would you ever know it since as soon as the round is chambered it fires anyway. It is the face of the bolt that gets overheated from the transfer of heat from the barrel/chamber to the bolt face and since the head of the cartridge sits right against the face of the bolt prior to pulling the trigger that heat gets transferred to the cartridge.

That is why you are advised against opening the feed cover when the barrel is overheated.

Cold, dirt, grease and grime cause jams and/or failures to feed...not "cook-offs."

Rick

What you describe as "the trigger failing to catch the bolt" (I'm not sure what that really means, but I'll use your terminology for the moment) would cause what is referred to as a "runaway" gun...not a cook off...and the only way to stop it is to twist the belt to stop cartridges from entering the feed tray... or to just wait till the sucker runs the entire belt dry.

The only good news is that you are in the safest possible position if this happens (behind the weapon) but that also means you will have to explain how and why you killed everyone in your squad!

Rick

Quote:

"Nothing is worse than ignorance in action."

But have you ever considered that God must love ignorant people...because he sure did make allot of them!

Rick

Primers in ammo will cook off at about 200 deg. F.

I appears that many of you are misunderstanding how open bolt firing systems operate.

There is no round in the chamber before the trigger is pulled. When the trigger is pulled it releases the bolt (that has been held to the rear under spring tension) which on its forward travel strips a cartridge from its link which is then pushed foward, chambered, and fired.

There is no provision for the weapon to chamber a live round through normal function without it being fired in the process so the temperature of the chamber has no direct effect on the round itself. Only the heat that has been transferred from the barrel/chamber to the bolt and/or the feeding mechanism could cause a live round to fire...but that would happen after the trigger had been released and the firing cycle had ceased.

Closed bolt systems could, theorhetically, have a chambered round fire due to a build up of heat from sustained firing but it is impossible in an open bolt weapon with a functioning firing pin. The live round is not in the chamber long enough before the firing pin strikes the primer to be effected by any heat that would be there.

If you have a chamber temperature high enough to instantaneously detonate a primer I think a round "cooking off" would be the least of your problems!

Rick

rick0311,

Now I am really confused. I asked this question because two members of AR, who I truly believe know their stuff stated that they have seen M60 and M1919 machine guns cook-off rounds.

DigitalDan said:

Quote:

---

AC, I saw M-60's cook off a number of times in Viet Nam. Door gunners sometimes tended to stay on the trigger and when things got hot there would be a very brief pause after they stopped firing, then "blam", a pause and another "blam". They usually would break the belt after the first or second shot. The guns did NOT continue like they were in full auto. As I recall it was 2-5 seconds to cook them off, and this is vague but I'm guessing about a 30 second sustained burst, or something like that to promote such an occurance. It is notable that we carried an extra barrel too, and ASBESTOS MITTS were SOP for a barrel change.

---

Robgunbuilder said:

Quote:

---

I had cook-offs with my M-16, twice with my M-60( as I remember) and most assuredly in a variety of air cooled Browning 1919's. When your barrel and chamber are glowing red hot ( a dull cherry as I remember) after a few hundred rounds in 30 seconds or so, in the early mornings( 1 to 2 am) in Vietnam cook- offs were a common problem. I personally never had a case blow although I heard that happened in the 1919 brownings on occasion.-Rob
All pure heat related, not due to firing pins getting stuck in the bolt. Those would be follow-thru's/slam fires a very different phenomenon.

---

Now you say it can't / doesn't happen. Well with the exception of the M16.

I am soooo confused!

ASS_CLOWN

Rick,



So M60 do cook-off. I didn't quite believe that. I figured that someone believed that cook off was the reason for runaway guns. Our MG doesn't cook off. The bolt face doesn't touch the round until it's pushed into the chamber. The bolt is normally caught by the trigger in a position far behind the tray and the ammo belt. i.e: the ammo remains cool until its fired. Now i know a little bit more about M60.



By the way. Dirt in the trigger unit, wrong lubricants (for the current temperature), high firing rate, e.t.c. causes runaway guns. Not cook off. Perhaps I expressed it a little bit unclearly earlier.



Sorry about the useless info

Ass Clown,

No need for confusion since what your friends describe follows exactly what I stated.

Any weapon (open or closed bolt) can, theoretically, have a round fire due to heat build up. The difference is that in an open bolt system (M60) it does not occure with a round in the chamber that will exit the barrel... where with a closed bolt system (M16) it could.

With a closed bolt system a round firing due to heat build up does not start an automatic firing cycle unless the trigger is pulled and the selector is on full auto when it happens. If the trigger is not held back the weapon will just fire, extract, eject and chamber another round that will sit there in the chamber until something fires it. This, of course, assumes that the rest of the weapon is functioning properly and the heat build up was the only cause for the round going off.

It has been my life experience that the vast majority of "accidental discharges" have far more to do with a connected human index finger and a disconnected human brain than they do with a malfunctioning weapon or heat build up.

Again...M60's (open bolt) DO NOT have a round in the chamber until the trigger is pulled and the bolt is released...M-16's (closed bolt) MUST have a round in the chamber or the gun will not fire when the trigger is pulled.

Machine gunners who practiced three-round taps seldom experience the problems that those who just yank the trigger back and hold it do.

Rick

You haven't yet mentioned which gun you are comparing to the M60.

The bolt on M60's isn't actually in contact with the round prior to pulling the trigger but it is within a few thousandths of an inch of touching it. Certainly close enough for radiant heat to transfer.

I would bet that "your" MG has about the same distance between the cocked bolt face and the round as the M60 does. The bolts on open bolt systems are not meant or designed to "slam" into the round when the trigger is pulled...they are designed to "push" the round forward into the chamber, forcefully...but not violently!

What hasn't yet been discussed is the heat build up from friction on all the moving parts of a MG during sustained firing. I would assume that this could also be a contributing factor in "cook-offs" in addition to the build up of heat coming from the barrel/chamber area.

Anyone who has every fired fully automatic weapons knows that the entire weapon gets hot when firing...not just the barrel and chamber.

Rick

Go back and read what I said.

I NEVER said "cook-offs couldn't happen"...what I was trying to point out was that most of you seemed as though you didn't really understand what caused them or what was actually taking place in the weapon when they happen.

The biggest difference (which I hope I pointed out) was that a closed bolt weapon (M16 type) is far more dangerous when, and if, this happens because the round actually fires as though you had pulled the trigger because the "cooked-off" round is in the chamber at the time.

With an open bolt weapon only the people in close proximity to the receiver are in any real danger...and only from hot gas and/or pieces of links that may be blown out by the escaping gas when the round goes off. The weapon cannot start firing because the empty case and the detached bullet will no doubt still be in the loading path and feeding mechanism...and the bolt is still being held to the rear. The situation then requires a safe cool-off period followed the removal of the debris from the mechanism and the removal of the crap in the crews pants!

Rick

Rick I sent you a PM.

ASS_CLOWN

Rick,
I will not give you any details about "our MG". I chose to leave out the actual name in the first place to avoid having my nationality revealed. I fear that the discussion may become a bit too patriotic and polarized.

The clearance between the bolt and inside tray rear end is 12mm in cocked position. So it slams the round allright. I have never yet experienced a "cook off round" but on the other hand, I'm probably dealing with a somewhat colder climate than you are.

Damn...your command of the English language certainly has improved over a very short period of time!

This topic is receiving far more attention and discussion than it really warrants based on the original question.

Forgive me...I certainly wouldn't want you divulging any national security secrets of your country!

I will stick to my original premise that ANY weapon (even your mysterious, unnamed MG) is subject to having a round go off because of a build up of heat due to sustained firing. While the actual chances of this occuring are not real high...the "possibility" nonetheless still exists and should never be totally ignored if one plans on safely handling weapons and keeping the friendships of those around us when we are firing those weapons.

No weapon ever made is 100% "foolproof" in its design or its functioning...not even foreign made mystery guns!

Rick

Olimahtes,

Based upon your email address posted in your Profile I would have to guess that the machine gun you are referring to is a PK of PKM. I have never played with one, though I would very much like to (maybe someday). I tend to agree with you regarding cook-offs. While there is a possibility of one occurring in the feed tray, I tend to believe the probability is quite small.

Of course it is always better to be safe than sorry.

ASS_CLOWN

Rick,
When were you in the Corps?

Semper Fi,
Craig

I have nothing but respect for the M60 gunner who can get that P.O.S. to actually keep firing with 3 round bursts. I tried to get it down to 6 rounds, but found it became less reliable. In fact, my favorite turned out to be a range between 12 and 18 rounds.

The M240, on the other hand, appears to enjoy ANY kind of burst; whether it be 3 round, or 50 round....

Back when we still had service numbers...not social security numbers!

As for your comment to the other guy about a "cook-off" in the feed tray...just keep in mind that with an open bolt system that is the ONLY place it can happen.

All I can say is that they must occur at some rate or why else would all of the manuals for these weapons speak of it and list the precautions and procedures for dealing with it when it occures ?

I have never had a ruptured case in any rifle I have ever fired and I have never witnessed anyone else having this happen either...so am I to assume from this and tell others that there is no way a case could rupture?

Rick

Sorry Craigster,

Got you mixed up with AssClown on the comment to our Russian friend with the secret machine gun.

The service number comment was certainly not meant as a slight to you at all...I was only referring to my own advancing age!

Semper-Fi right back at ya, brother!

Please don't even get me mixed up with ASS CLOWN.

The M60 does have the potential to cook off rounds and the Army trained recruits to drop the hinged cover immediately and move away from the weapon,if you saw a live round present after firing and opening the weapon. This was a known weakness along with the hinge on the cover being a weak link and prone to breaking.

RMK,

So the M60 is perhaps an even bigger POS than the old BAR. Will the US military ever learn?

ASS_CLOWN

Uh, the M60 is ancient history, fyi. And what, precisely, was wrong with the BAR? It's no Bren, but....

The M240 appears to work okay, and the SAW works good, too, from my experience. Actually, in the hands of a skilled operator, the M60 was okay, provided you sacrificed the chicken correctly, etc..

120mm,

Well all I have ever heard about BARs is that the forearms catch fire, the recoil springs anneal and then the rifle doesn't work anymore (well I suppose it makes a good heavy weight club), the magazines would rock around in the weapon and cause jam after jam, etc, etc, etc. For WWI it was great, but not for long afterward, at least from what I have been told and read. You are right about one thing though, the BAR was most definitely NO BREN, thank God.

It is my understanding that the M60 was nothing more than a MG42 basic receiver with a Bren barrel assembly grafted to it.

ASS_CLOWN

Isn't it amazing how the US military has managed to kick the crap out of every single enemy they have faced on the battlefield in the last 100 years (Germany twice!) when we have such poorly designed weapons that fall apart and malfunction so often????

I joined the Marine Corps in 1963 and had the pleasure to personally know and to learn from some senior NCO's who had fought in both WWII and Korea and to a man I never heard anything but good things about the BAR from them.

The only weapon problems that I recall experiencing or even hearing about in Vietnam were ones involving M16's when they were first issued...and those problems were soon worked out. I never did like the puny caliber but that had nothing to do with the functioning or reliability of the weapon once they issued cleaning gear (duh!), chromed the chamber, and used the correct powder in the ammunition.

Rick

Some comments about the BAR I found :

The initial M1918A1 version of the Browning Automatic Rifle (BAR) was first used in combat by American soldiers during World War I, and many saw service in World War II. The BAR received high praise for its reliability under adverse conditions.

In 1940, the model M1918A2 was adopted. Unlike earlier models, it could only be fired in two automatic modes--slow (300 to 450 rpm) or fast (500 to 650 rpm)--but not in semiautomatic mode. Both versions were widely used in the second world war. The USMC preferred the semiautomatic mode in some tactical situations, and modified most of the M1918A2 guns to include that capability. A buffer spring in the butt greatly reduced recoil, to the advantage both of firing accuracy and shooter endurance.

The M1918A2 also mounted its folding bipod (2.38 pounds!) on a special flash hider near the end of the barrel. Since the bipod could easily be detached in this model, it very frequently was! but not often in defensive positions, where it was very effective. The flash hider, which was the point of attachment for the bipod, was not usually removed. Hiding the flash from enemy troops when firing on them isn't the purpose of the hider, all automatic weapons are easily visible when fired at night. It blocks the muzzle flash from the vision of the shooter, maintaining his night vision. That's important!

The Army infantry squad of nine men was tactically organized around a single BAR. The Marine squad of thirteen men was organized around three fire-teams, each organized around a BAR. The much greater fire power of a Marine platoon with its nine BARs over the Army platoon with its four BARs was a great combat advantage.

The BAR was a popular weapon in WWII and Korea, because it was very reliable and offered an excellent combination of rapid fire and penetrating power. The BAR's only serious drawbacks were its lack of a quick-change barrel (to reduce the chance of overheating), and its weight (BAR, with bipod and a loaded bandoleer, came to about 40 pounds).

In Korea, the much greater range and penetrating power of the BAR and the .30 caliber air cooled machine gun, firing rifle ammunition, usually more than offset the light weight and rapid fire capability of the variety of submachine guns the North Koreans and Chinese used, including their burp guns modeled on Soviet weapons such as the Shpagin PPSh41 , which fired pistol ammunition.

The BAR suffered from being designed for one purpose but primarily used for another. It was designed during WW1 for 'walking fire', a concept which had the troops walking towards the enemy, firing from the hip as they went. Not terribly sensible in most circumstances.

So it was pressed into use as an LMG instead, in which role it had some significant disadvantages compared with the Czech ZB series (which includes the Bren). Primarily these were the fixed barrel, and the small-capacity bottom-mounted magazine (a good Bren crew could change mags so fast there was hardly a pause in the firing).

However, the BAR (like the Bren) did have the essential merit of reliability, plus good target effectiveness when it hit. So it was greatly liked by most users, which is what counts.

Having said all of that, I don't know of any major battle in which the quality of the small arms affected the outcome, at least not since the Franco-Prussian War of around 1870 when the 'needle gun' proved a decisive advantage. There may also have been some serious smaller-scale consequences with the early M16 problems.

Generally speaking, all that matters is that the guns work.

Tony Williams: Military gun and ammunition website and discussion
forum

Geetings from across the pond!

I totally agree with you...and forgive me for leaving out our British allies who helped us to kick the crap out of Germany...TWICE!

Rick

Rick,

If the BAR and the M60 were/are so great, then why the constant statements on the net about how bad they were/are? My comments about these two weapons are based off of what I have learned in forums such as this one. Are these guys making this stuff up?

RMK and 120mm have both spoken out to the significant deficiencies of the M60. I am sure I can find comments here at AR about the BAR annealing it's recoil spring (thus rendering the rifle worseless), about is forearm catching fire, etc, etc.

ASS_CLOWN

First of all, Ass Clown...if you haven't noticed it yet many people in this world (especially on the interent) are quite fond of trashing things that they really have very little practical knowledge of. Pin them down and the vast majority of the time they are relating stories from others...who are relating stories from others...who are relating stories from others!

As I told you in an email, I have heard numerous supposed combat veterans relate stories about seeing people "blown-off their feet and thrown backwards" when being hit by small arms fire. A physical impossibility...but still a very commonly made claim by people who will swear on their childrens lives that they witnessed it.

I don't know the backgrounds of the people you consider to be experts on this topic but I do know, from personal experience that ANY weapon (I don't care what type or who made it) that is used in a combat environment is far more apt to experience certain problems than it would under other circumstances. People firing and using weapons at the range seldom do so with massive amounts of adrenaline pumping through their bodies.

Combat does not always allow for proper and timely cleaning and maintenance and people getting shot at seldom have 100% accurate recollections of the small details of the incident when retelling the story.

The BAR and the M60 and its variations, have probably fired more rounds in combat than any of the other weapons you have touted as being so much better. Have they had malfunctions?...of course they have.

Based solely on some of the questions and comments on this thread I am quite convinced that more than a few of the people participating in the debate have very little practical experience with heavy, medium or light machine guns...nor do they present a basic understanding of the principals, functioning and dynamics involved in an open bolt machine gun design.

I am not claiming now...nor have I ever claimed that either the BAR or the M60 is better or more superior to other weapons of their class. What I am saying is that both of these weapons have a very good and very long proven track record in actual combat all over this planet.

The BAR was designed by the same man that designed the M2 .50 caliber, the M1919 .30 caliber and the 1911 pistol...which are all still serving our military and many other armies quite well after almost 100 years. All of these weapons were used in WWI, WWII, Korea, Vietnam, Desert Storm, Afghanistan, OIF...and more small conflicts around the world than you could even begin to list. They have been used in combat in humid jungles, dry mountains, buring deserts and freezing snow.


Rick

Rick,

So you are saying these individual are either relating BS or not comprehending what actually happened to them in combat situations due to the stress of the situation. That seems perfectly logical to me. Do you think that may be the case with those that state how great some weapons are, the Kalashnikov and the Bren come immediately to mind?

ASS_CLOWN

Look,

This "my dad is tougher than your dad" argument can go on forever and no one will ever change their opinions or views on the subject.

As I have repeatedly stated...malfunctions, stoppages, parts breakage, and any number of other problems can ALL "theoretically" occur in ANY weapon at ANY time no matter how well it was designed, manufactured or maintained. Shit happens...and stuff breaks and it always seems to occur at the worst possible time in combat.

My issue was with people claiming that M60's were (as you continually stated) pieces of shit...and that BAR's weren't much better. Those statements are just patently untrue.

One car always wins the race...but that does not mean that ALL the other cars are pieces of shit that have design and/or manufacturing problems.

I have no reason to doubt that your friends may have experienced a malfunction of some sort if they spent much time behind a weapon in a combat zone. If we had a forum with nothing but ex-Soviet soldiers speaking up I can guarantee you that you would be hearing horror stories about their weapons jaming and malfunctioning while hords of Afghans charged them.

Despite what some may feel, weapons that are true "pieces of shit" do not stay in service for very long in the military. They either get modified to fix the problems, or they get replaced. The early problems with the M16's in Vietnam did not last for very long until the weapon was modified to address the complaints from the troops in the field.

I have had military people tell me that the M9 Beretta pistol is by far the best pistol ever manufactured...and I have had other military people tell me that it isn't worth the powder to blow it up. The "truth" more likely fits somewhere in the middle of these two ridiculous statements.

Rick

The m9 may be ok but the units with any likelihood of using a pistol are occasionally issued .45s of some manufacture. btw I'll attest to the effectiveness and reliability of the m60.