MG rates of fire.

[Guest kip anderson]

Hi,

When designing a machine gun there are a number of problems that have to be overcome. One of the biggest problems is how to deal with heat, particularly heating of the barrel and the chamber the round sits in before it's fired. When a round is fired there are two sources of heat, the propellant gases and friction between the bullet and the bore. Friction accounts for a very small amount of the heat transferred to the barrel; it's the propellant gases that are the problem. For a fraction of a second after a round is fired the gases reach a temperature of 2000degrees C and some of this heat is transferred to the barrel.

Barrels can be regarded as heat "sinks", they heat up quickly but if air cooled they cool down more slowly. When a barrel reaches a temperature of arround 500degrees C three things start to happen.You start to get "cook off" , which is when a chambered round ignites before it's struck be the firing pin due to residual heat; the rifling is stripped off by the friction of the bullet and you get barrel droop. All these factors make the machine gun unusable and the critical temperature is normally taken to be 475degrees C. The big question is how long does it take an air-cooled barrel to heat up to 475degrees C at a given rate of fire? Some examples follow that attempt to anwer this question.

1)A Stoner 63A LMG firing at a rate of 50 rounds a minute will take fifteen minutes to reach 475degrees C.

2)A SA80 assault rifle firing at 60 rounds a minute will take six minutes to reach the temperature at which "cook off" starts.

3)A Bren gun LMG firing at a rate of 120rds/min. will require it's barrel changed every two and a half minutes.

In summary one can make a small table of the above examples.

Rate of fire. Time weapon can be fired.

50rds/min. 15 minutes

60rds/min. 6 minutes

120rds/min. 2 and a half minutes.

Sadly I am not really computer literarate or I could enter the equations governing the heating of barrels and you could all work out for yourselves the possible duration of fire at any given rate of fire before jamming. The important piont to emerge is that a machine guns use-able rate of fire is below the "cyclic" rate of fire that is so often quoted. The German MG42 had a "cyclic" rate of fire of 1200rds/min. the US.30 M1919A4 a cyclic rate of 450rds/min. Yet even the M1919's cyclic rate is far above that which either weapon could achieve in the real world, assuming no extra barrels for the MG42.

Of course the MG42 and most modern machine guns had a quick change barrel so it would be interesting to see what happens when a crew have more than one barrel.If I once again use the Stoner63A LMG firing at a rate of 50rds/min.but this time with one spare barrel this is the result.

2000 rounds fired in forty minutes with each barrel being changed every five minutes results in barrel one being at 395degrees C, barrel two being at 410degrees C and the trigger being at 62degrees C. Once the barrels have been changed the first time they tend to increase from 300degrees C to 400degrees C during their five minutes of firing while the cooling barrel decreases in temperture from 400degrees C to 300degrees C, and so on. However over all the temperture of the barrels increase as the barrels cool slightly less in five minutes than they heat when being fired over the same period at this rate.

At this point its important to remember the exponential nature of the rate at which barrels heat up given even a small increase in the rate of fire above 50rds/min. If you increase the rate of fire to 60rds/min. the barrel heats from 300degrees c to 400degrees C in about two minutes.This in turn would mean that the cooling barrel would only have two minutes to cool, thus falling from 400degrees to 350degrees before it was its turn to be used again. Both barrels would reach a temperture of 475degrees C in about 17 minutes, from a cold start. To maintain a rate of fire of 75rds/min. for 15 minutes you would require two spare barrels and four spare barrels to maintaina rate of fire of 100rds/min. for 15 minutes.

Given the above what are the implications for CM if any? The major implication is that in my opinion, others will differ, the firepower of the MG42 in both LMG and HMG roles is overstated.In the LMG role it will have had a use-able rate of fire no greater than that of the Bren gun, or in CM2 the Soviet 7.62mm Degtyarev DP LMG.All three guns will have been restricted in their rate of fire by the problem of over heating at rates of fire far below the cyclic rate of even the Bren, the slowest of the three.(Assuming no spare barrels for the MG42 in its LMG role.) Indeed in the fifties when Britain was about to change to the 7.62 NATO round a report concluded that although the MG42 was a better all round weapon, in the LMG role the Bren was superior. As a result Britain kept the Bren until the 1980s in 7.62mm.

If you assume two spare barrels for the MG42 in its HMG role then its firepower should only be 50% higher than the M1919A4. Two spare barrels would give a rate of fire, over fifteen minutes, of 75rds/min. for the MG42 against 50rds/min. for the non-barrel-changing M1919. However I have no idea how many spare barrels German HMG teams had in reality.

It's worth remember that the three most famous machine guns developed as a result of the experience of WW2, the M60,FN MAG and Soviet 7.62mm PK, all have cyclic rates half that of the MG42. If the MG42's high cyclic rate had been a positive, rather than negative characteristic, it would have been copied post war. Non of this detracts from the fact that the MG42 was the "gold standard" machine gun to come out of WW2. Its just that the characteristic it's most famous for, its high cyclic rate, was not a positive feature.

Sources.

Small Arms, DF Allop and MA Toomey. Brassey's 1999. A textbook written by lecturers at the Royal Military College of Science, Shrivenham, UK. ISBN 1 85753 250 3.

Jane's Infantry Weapons 1993-4, and 1999-2000.

All the best,

Kip.

Stunning game, am still in shock!

------------------

[Guest Germanboy]

When I was trained on the MG3 (successor to the MG42 in the Bundeswehr), we were only shooting bursts - that was as LMG, and from the kickback I would think it is impossible to do a constant of no-matter-how-may-rounds/minute. So for an LMG this would be an academic argument, since in reality you never find yourself firing a constant amount of rounds per minute.

For HMGs? Dunno.

Anybody else here? Surely that has been addressed before?

------------------

Andreas

It is amazing what you can learn from a good book...

[Guest Big Time Software]

Hi Kip,

We disagree that the RoF is a negative when it comes to firepower. This issue has been debated several times already. One thing to keep in mind is that no MG can fire sustained for any significant length of time before heat overcomes it. Last summer I watched a lovingly cared for M60 jam up twice after expending only 250 rounds of sustained fire. After the second jam the owner gave up and let it just sit there. In practice sustained fire like this was not generally possible do to a host of factors, not the least of which was a limited ammo supply.

The main benefit of the higher RoF is more accurate bursts (tighter grouping) and therefore higher lethality for each short pull of the trigger. It is also better at suppression since it can put more lead onto a target in a shorter space of time than could something like a Bren or BAR. It was also belt fed, which both of these guns were not, which also is a huge plus in its favor. Then there was the psychological effect of the MG42, which was so real that the US Army had to make special training films and falsified technical reports to try and undermine its effect on men being shot at by it.

As for changing barrels, all LMG 42 teams had at least ONE extra barrel. They often had two. The heat issue is one that plagues all full auto weapons. The quick barrel changing of the MG42 compensates somewhat for its high rate of fire. A barrel could be swapped out in about SIX seconds but a semi-experienced crew.

The cyclical rate is, as you say, not the practical rate. Recoil was one limiting factor, while Ammo usage was one of the biggest. And this is one reason why the RoF of post war MG42 based weapons have a lower RoF (but higher than most WWII MGs!) because it was found that 1200 was overkill and often led to inexperienced crews firing off too many rounds too quickly.

As for the MG42 LMG being too powerfull, it is only about 30% greater than the BAR and 20% greater than the Bren. The belt feed and quick barrel change should give it at least this much of an advantage.

As for the HMG 42, it has the advantage of a superior platform and optics. Therefore it has advantages that have nothing to do with RoF. All the same advantages/disadvantages as the LMG apply, except that there was generally far more ammo and at least two spare barrels available for its use.

On balance I think the high rate of fire was simply unnecessary rather than it being inherently negative. The rapid expendature of ammo by increasingly less experienced crews was an indirect cause of great concern to the German Army during the last months of the war.

Steve

[Guest kip anderson]

Hi,

I should make clear that I have no experience in using machine guns. What I posted all comes from what could best be called "academic" books. Those with actual experience of MGs have the edge on me.

What got me thinking is that I saw on a screen shot from a beta build that at 500 yards the MG42 in its LMG role had twice the firepower of the Bren gun, 18 to 9 I think. This made me think of the UK report I read which concluded that in the LMG role only, the Bren was the better gun. I then read up on the subject and came up with the above. Clearly this is a matter you have considered and I am more than happy to go with Steves conclusion.

Cracking under the strain of waiting for the game to arrive.

All the best,

Kip.

------------------

[Guest Big Time Software]

Kip,

Your approach wasn't that off. The one thing you missed was the fact that no MG lasts very long if it fires sustained. And the warmer it is, the less time it takes for the gun to have a serious jam. The M60 gunner I mentioned had a bear of a time removing the first jammed casing, while the second one he couldn't get out until he let the thing cool down for a while.

So the benefits of the RoF are more related to shorter bursts. It looks like 1200 was overkill, but 400-500 was a little below optimal.

The Bren was a good gun, but I am not sure why the Brits found it to be superior to the MG42 in the LMG role. It certainly had its good points, and was a darn fine weapon, yet I am left wondering what made it a "better" LMG. What did the report give for reasons?

Steve

[Guest Germanboy]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Big Time Software:

The Bren was a good gun, but I am not sure why the Brits found it to be superior to the MG42 in the LMG role.

Steve<HR></BLOCKQUOTE>

The English also think they are good at Cricket...

Being cruel tonight...

------------------

Andreas

It is amazing what you can learn from a good book...

[Guest kip anderson]

Steve,

The report on the Bren I read some twenty years ago before I became a fully paid up military history/technology nerd.The one reason I do clearly remember is not related to heat but to the recoil on the MG42 in the bipod mode. The report claimed that the recoil was difficult to control and that using the bipod the weapon was not as accurate as the Bren. The stuff on heat came from a recent military textbook.

And being a New Zealander living in the UK I can confirm that the Brits are not too hot at cricket!

All the best,

Kip.

PS. I should add that I have no special passion for the Bren I just want everything in CM to be as close to reality as possible, minus the blood, which it seems to me it is thanks to Steve and Charles and all the others that helped them.

PPS. It crossed my mind, what is the firepower of the water-cooled Vickers in CM?

Thanks.

------------------

[Hunter]

Kip, BTS,

What's all this about recoil? My experience with the M60 (OK, different gun) would suggest that recoil isn't a problem at all, and certainly nothing like firing a FN FAL or similar.

Is it true that the 42 had particular recoil problems?

Bruce

ps: And where are the animations of the MG42 team putting on gloves and changing the barrel after a JAM; dammit

[Mark IV]

Compared to MG34, and probably the Bren, the much higher rate of fire of MG42 caused lower overall accuracy in the bipod mode.

At more than twice the ROF (1200 v. 500rpm), increased vibration and recoil are unavoidable. The effect is offset by its cause: the higher ROF creates a tighter string of lead.

I like the Bren, but the 30 round box magazine is a real limitation in some situations. The crew was required to change mags far more often than barrels, so more down time overall for care and feeding.

[tss]

Hunter asked:

Is it true that the 42 had particular recoil problems?

Yes. In soc.history.war.world-war-ii one German veteran once stated that he was physically too light to be a MG-42 gunner; when he had to shoot one in training he was actually pushed back by the recoil.

- Tommi

[Guest Username:]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Mark IV:

At more than twice the ROF (1200 v. 500rpm), increased vibration and recoil are unavoidable. The effect is offset by its cause: the higher ROF creates a tighter string of lead.

B]<HR></BLOCKQUOTE>

This is only correct if you are comparing weapons of similiar weight. The weight of a weapon has one benefit, it reduces vibration. The increased mass will "stall" the effect of the individual impulse load till the bolt returns forward. This smooths out the system just like a balanced car engine runs better at higher RPMs.

The use of the tripod (on the MG42) adds weight to the overall weapon, this stabilizes the system as much as the extra leg. It adds a damping effect. If you have seen a mg42 firing with a tripod, you will notice that when the weapon stops a burst, there is a backwards jump (recoil). Even this can be reduced by sandbagging the legs further. The "recoils" are damped out by the reciprocating mechanism of the bolt in the weapon while firing also.

In the bipod role, germans would have the teen loader hug the gunner to add his weight to the gunner (Fionn no need to quote any percentages on anything please!).

I am not sure what this tighter string of lead means to you. Is it distance between bullets?

I have said it before. If the germans had a 3-5 shot interrupter option for the MG42, then its ROF would have been a non issue in the bipod role. I still think it would be a good option for present LMGs.

Lewis

[Mark IV]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Username::

I am not sure what this tighter string of lead means to you. Is it distance between bullets?

Yeah man. With a round headed downrange every .05 secs you get a tight group. Even if the muzzle is jumping, the gunner is putting more lead in the target area with less chance of individual rounds deviating.

I have said it before. If the germans had a 3-5 shot interrupter option for the MG42, then its ROF would have been a non issue in the bipod role. I still think it would be a good option for present LMGs.<HR></BLOCKQUOTE>

Lots of modern assault rifles and subs have this feature (M16A2, FN/FAL, MP5, etc.). I don't know when it was invented, but I can't think of any WWII-era weapons that used it, offhand.

[Guest Michael emrys]

Although I can't quote a source offhand, I believe Username is correct in stating that the MG 42 had a three shot burst option. In fact, what I recall is it had an odd kind of trigger that looked like two triggers joined together and pivoting in the middle. If the gunner pulled the upper part, he got a three shot burst. If he pulled on the lower part, he could get a sustained burst. Er...unless I've got that backwards.

The other thing about maximum cyclic rates of fire... Most infantry MGs had a cyclic ROF of around 500-600 rpm. As Steve said, this had more to do with ammo usage than barrel wear, since gunners could be trained to fire in short bursts that would limit barrel heating, but the higher rates would still eat up a lot of ammo. That's why a German squad consisted of an LMG gunner and nine guys to carry ammo for him. But the ripping sound of the MG 42 was such a powerful psychological force, daunting to enemy morale, that it was thought worth keeping.

It is of some interest that the versions of the Browning machine guns carried on aircraft (at least the ones on fighters; I have not confirmed this for bombers yet) had a cyclic ROF of 1,000 rpm. Overheating does not seem to have been much of a problem for them, though they too were encouraged to fire short bursts.

As for the Vickers water-cooled mediums, the sparse information I have for them suggests that they were indeed capable of longer sustained bursts without overheating. The big problem with them was that they weren't very portable and were thus of only limited usefulness. I think they were pretty much phased out of first-line units after about 1942.

Michael

[This message has been edited by Michael emrys (edited 05-23-2000).]

[Guest Username:]

1. I said "IF". The MG42 was full auto. The early MG34s had the center rocker fire selection trigger. That was single shot or full auto. I dont believe ANY WWII MG had this option but it WOULD have been great.

2. I know GIs modified brownings for ground use to fire at a higher cyclic rate. The extra weight of the weapon helped. I believe they just removed metal from the bolt somehow.

Lewis

[Lee]

That is why we have water cooled guns. Nothing beats a water

cooled for sustained fire. You can put out masses of fire with

those. Great for stopping assaults or keeping the enemies' heads

down. =) Heavy to tote, but when you want real firepower, there

is no alternative.

The MG-42 does have an incredibly high rate of fire, but that can

be a real asset at times, like when conducting an ambush. You

can plaster the enemy before he knows what hit him. 8) Steve has

a good sound in for the MG-42 in CM, but you have to hear one in

person to truly know. The sound is just amazing. I can understand

G.I.'s being afraid of them.

I don't like burst limits on guns unless there is also an option

to fire full auto. I like to be the burst controller, not some

mechanical device deciding for me. When you need the firepower of

full auto you tend to *need* it. And such devices can get you killed.

[Mark IV]

That is why we have water cooled guns. Nothing beats a water

cooled for sustained fire.

'Cept maybe a multi-barreled chain drive...

I like to be the burst controller, not some

mechanical device deciding for me.

Those little burst mechanisms add a lot of moving parts, and the potential for failure is believed to be higher. Some of them use really scary-looking little ratchet mechanisms that I wouldn't want between me and Salvation.

And on normal rate MGs they seem to be a sort of mechanically-enforced fire discipline. I never had a problem firing 2-4 round bursts with M16A1, M3A1 (no challenge there, even to fire single rounds), and the M73 and the cupola .50 on the M60 tanks.

On MG42 they might have served a useful purpose.

[Guest Big Time Software]

When firing an MG2 (post war modified MG42) I found no problem sending bursts of 5 rounds or so down range at roughly 1000 rnds/min. But then again I wasn't being shot at I think that a burst mechanism for the MG42 would have been an asset as the training and soldier qualities declined. Of course, a heavier bolt to reduce the RoF might have also been a solution.

Steve

[Guest Big Time Software]

Kip,

Thanks for the follow up. I think I personally would have taken the MG42 over a Bren, but then again I am fortunate enough to not have had to handle either one under fire so who really knows

Steve

[KiloIndiaAlpha]

We had a similar thread some time ago.

There is a great deal of difference between the spec of a weapon- what the arms dealer will tell you and the gritty reality of how it really performs. The SA-80, for example, is in principle, a 'good' weapon, however if you hit someone with it-I mean physically hold the barrel with two hands and whack them with the stock you will probably break it.

Belt fed weapons sound great- high rof, accurate etc etc. Try carrying belted ammo through even light undergrowth- your guaranteed a jam within 5 seconds of use. (Due to belt damage, lost cartridges, bits of tree in the belt...) Use a mag fed weapon with 1 less cartridge than the mag is designed for, with a good no 2 your rof will be high with much less risk of a jam at the wrong moment...

[Guest Username:]

Supposedly the MG42 was tolerant of alot of real world abuse. German soldiers certainly swathed themselves in belted ammo and it was common practice to go into battle like this. I cant believe what KIA is describing is true for WWII german '42s.

Most modern armies insist on keeping belted ammo in ammo boxes with weather sealing. If for nothing else but NBC washdown. I dont know what modern army experience KIA has (the type that breeds online stalkers I guess) but the US Army had a policy of keeping ammo in the cans unless you were the assistant gunner.

Lewis

[Guest Germanboy]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Big Time Software:

When firing an MG2 (post war modified MG42) I found no problem sending bursts of 5 rounds or so down range at roughly 1000 rnds/min. <HR></BLOCKQUOTE>

3-5 round bursts were what they tried to get into us on the range with MG3, IIRC. Long time, brain mushy. Of course that was a forlorn hope with me.

Re: jams Our comrades from first platoon in basic training had a very stupid Corporal who once decided to demonstrate his manlyhood by extracting a training round that had jammed without waiting while the gun was hot. Needless to say, it went off while he was at it, and he lost half his hand. That's evolution for you... I sure was glad not to be in that platoon. Our platoon was trained on the 20mm twin AA gun and no real ammo, so no trouble.

------------------

Andreas

It is amazing what you can learn from a good book...

[Guest JonS]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Michael emrys:

As for the Vickers water-cooled mediums, the sparse information I have for them suggests that they were indeed capable of longer sustained bursts without overheating. The big problem with them was that they weren't very portable and were thus of only limited usefulness. I think they were pretty much phased out of first-line units after about 1942.

<HR></BLOCKQUOTE>

Michael

Commonwealth divisions continued to use the Vickers in MG Bns till near the end of the war. For eg, the 2(NZ) Div MG Bn was only disbanded in early '45 (Feb?), and then mainly to provide replacements for depleted rifle bns rather than because it had ceased to be useful.

The support bns provided long range - including indirect - suppresive fire for, well for whatever really, but often as part of an integrated fireplan. The shoots would generally be quite long (in time, as well as range) so the water cooling would be an especial advantage in this situation - and the weight not such a disadvantage.

Regards

Jon

------------------

Ubique

[Lee]

That is why we have water cooled guns. Nothing beats a water

cooled for sustained fire.

---------------------------------------

Mark IV

'Cept maybe a multi-barreled chain drive...

---------------------------------------

Note, I said "sustained fire". A gatling will put out a horrendous

volume of fire, but it can't do it for long or you'll melt the barrels.

[This message has been edited by Lee (edited 05-23-2000).]

[Guest Username:]

I think the germans would have been better off producing a heavy barrel version of the MP44 with a bipod as the squad automatic and moving the MG42 up to a platoon weapon. Perhaps one squad in the platoon would have a mix of tripod and bipod 42s and the other two squads would be based around the above fictional weapon as well as regular MP44, SMG and rifles.

I read that the german infantry were responsible for belting up all that ammo for all those MGs. Seems like alot of work. It would have helped to have all the weapons and tools together.

lewis

[Pacestick]

My two cents worth on MGs

Cyclic rate of fire is only used in emergencies. Most MGs are fired according to laid down rates of fire that are determined by the amount of ammo that can be carried and the problem of heat dissipitation and barrel wear. For example the GPMG M60 we carried in our rifle sections had three rates of fire:

Normal-bursts of 5 to 10 rounds as required(see a target, fire until destroyed)

Sustained-bursts of 5 to 10 rounds at 100 per minute.(used to cover movement or suppress a position)

Rapid-bursts of 5 to 10 rounds at 200 per minute.

A rifle section in the advance carries 800 rounds( 8 x 100 round belts at 7lbs per belt) of MG ammo as a first line which gives 8 minutes of sustained fire or 4 minutes of rapid fire, obviously fire control orders and fire discipline are of paramount importance.

It takes 15 seconds to change a barrel and it is supposed to be carried out every 200 round fired. A gunner is concerned about heat because of cookoffs and he cares little about barrel wear,consequently, changes are usually carried out when the barrel is white and hot enough to light a smoke from

Belt fed MGs are far superior to mag fed guns because of the ammo that can be carried, a 100 round belt comes in a cloth bag which can be draped over a shoulder. A 100 rounds for a Bren has to be placed in 3 x 32 round magazines which are far more difficult to carry.

The Bren has two trigger pressures, the first fires a single shot , the second fires bursts.

The jammed M60 mentioned was more likely caused by the user not greasing the feed mechanism rather than from heat.

My experience is obviously post WW2 but I am sure the infantry soldiers in that era had similar problems in combat. There is only so much a grunt can carry and be effective, you give him an extra belt of ammo and a grenade has to be left behind and so on.

Peter