Machine Gun RPM Discussion

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Tony Williams

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Scott Kenny said:
The neat trick is that the Sherman coax used the same mounting points as the ground M1919 .30cal and M2 .50cal.

If your tank crew wanted a .50cal coax, you needed to acquire a .50 from somewhere (as simple as the AA pintle if you're a US tank) and then pull out the M1919 coax. The whole swap took about as long as putting either M1919 or M2 onto a tripod.
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British Army coax guns and ammo were a mess. First you have the Vickers in .303 inch, then they chose the Besa in 7.9mm as a replacement, and finally they acquired the Browning in .30 US. Three different weapons using three non-interchangeable types of ammo. At the same time the RAF were using the Browning in .303. The RAF version is interesting because the gun design was modified so that it fired from an open bolt, thereby avoiding the the problem of cook-offs caused by overheating the breech. This would have been useful to have anyway.

With the benefit of hindsight they could have avoided all this by adopting the Browning in open-bolt form but with a much heavier barrel and a reduced rate of fire. Then when US AFVs came along, it would be a simple matter to swap out the .30 Browning for the .303 version.
 
Pardon me, missed this.

Tony Williams said:
British Army coax guns and ammo were a mess. First you have the Vickers in .303 inch, then they chose the Besa in 7.9mm as a replacement, and finally they acquired the Browning in .30 US. Three different weapons using three non-interchangeable types of ammo. At the same time the RAF were using the Browning in .303. The RAF version is interesting because the gun design was modified so that it fired from an open bolt, thereby avoiding the the problem of cook-offs caused by overheating the breech. This would have been useful to have anyway.
Click to expand...
Yes and no. The closed-bolt Brownings could be fitted with a synchronizer gear so they could fire through the prop. In the 1920s and 30s, even into the early 1940s, that was desired by a lot of requirements writers. (See the P-40 and early Mustangs with cowling guns on the US side, and both Bf109 and Fw190 on German side, not sure about British planes with cowl guns).

Open bolt guns are better for ground MGs, where you don't have 200-300mph wind chill and below-freezing temperatures to keep your guns cool.


Tony Williams said:
With the benefit of hindsight they could have avoided all this by adopting the Browning in open-bolt form but with a much heavier barrel and a reduced rate of fire. Then when US AFVs came along, it would be a simple matter to swap out the .30 Browning for the .303 version.
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No, you want/need a high rate of fire on aircraft MGs (and AAMGs), to get a large weight of shell on target in as short a time as possible. You do not need a ShKAS rate of fire on the ground, MG42 notwithstanding. There's a reason the MG1 and MG3 were slowed down to 800-900rpm instead of 1200-1500!
 
Eyeah for ground work 600 to 900 rpm is the best.

Sure 1000 plus sounds amazing.

Until you stop to think longer then 15 seconds.

Or try to carry 1000 bullets, plus 50 pounds of stuff, 10 miles by foot.

The MG42 was notorious for its hunger for bullets and was noted to be an out right PAIN to keep fed.

Which is why you dont see gatling or revolver style guns on ground vehicles outside of specialize roles that can be summed up as AA work.
 
Firefinder said:
Eyeah for ground work 600 to 900 rpm is the best.

Sure 1000 plus sounds amazing.

Until you stop to think longer then 15 seconds.

Or try to carry 1000 bullets, plus 50 pounds of stuff, 10 miles by foot.

The MG42 was notorious for its hunger for bullets and was noted to be an out right PAIN to keep fed.

Which is why you dont see gatling or revolver style guns on ground vehicles outside of specialize roles that can be summed up as AA work.
Click to expand...
I was very fond of 600rpm. M60E3 goes chopchopchop...
 
Firefinder said:
Eyeah for ground work 600 to 900 rpm is the best.

Sure 1000 plus sounds amazing.

Until you stop to think longer then 15 seconds.

Or try to carry 1000 bullets, plus 50 pounds of stuff, 10 miles by foot.

The MG42 was notorious for its hunger for bullets and was noted to be an out right PAIN to keep fed.

Which is why you dont see gatling or revolver style guns on ground vehicles outside of specialize roles that can be summed up as AA work.
Click to expand...
Firefinder said:
Eyeah for ground work 600 to 900 rpm is the best.

Sure 1000 plus sounds amazing.

Until you stop to think longer then 15 seconds.

Or try to carry 1000 bullets, plus 50 pounds of stuff, 10 miles by foot.

The MG42 was notorious for its hunger for bullets and was noted to be an out right PAIN to keep fed.

Which is why you dont see gatling or revolver style guns on ground vehicles outside of specialize roles that can be summed up as AA work.
Click to expand...
Then why did the US Army install 7.62mm Gatling guns on some of the Humvees driven by Green Berets in Afghanistan and Iraq?
 
riggerrob said:
Then why did the US Army install 7.62mm Gatling guns on some of the Humvees driven by Green Berets in Afghanistan and Iraq?
Click to expand...
Cause they are special forces doing SPECIALIZE raiding as such can do what ever the fuck they want and not some poor line guys who are doing 4 day foot patrols which is the actual meat and potatoes of military work.


Also needs to be mention that they used them for all of 6 weeks before pulling them for 240s cause they kept running out of freaking ammo.
 
Hi,

Firefinder said:
The MG42 was notorious for its hunger for bullets and was noted to be an out right PAIN to keep fed.
Click to expand...

I didn't check the WW2 manuals, but a 1960 Bundeswehr pocket manual describes the tactically realistic maximum effective rate of fire of the MG42 as 120 to 160 rounds per minute. The British expected 120 rounds per minute from the Bren gun:


You might have seen this ... German soldier operating machine gun as he's been trained to:

View: https://www.youtube.com/watch?v=B-VJERTwTJc&t=25s


Regards,

Henning (HoHun)
 
Comes down to logistics ?
Do you hump yet-another box of belt, or the spare barrel you'll need to fire it through ??
 
I believe the concept behind the German focus on very high rates of fire for their infantry MGs was that in normal circumstances enemy infantry would only be exposed for brief periods of time. So, when you catch them in the open you want to send as much fire as possible downrange before they can move into cover. There is some logic to this, but penalties that come with that high rate of fire. In intense combat green troops must be likely to fire excessive amounts of ammunition and ruin barrels.
 
Hi again,

HoHun said:
I didn't check the WW2 manuals, but a 1960 Bundeswehr pocket manual describes the tactically realistic maximum effective rate of fire of the MG42 as 120 to 160 rounds per minute. The British expected 120 rounds per minute from the Bren gun
Click to expand...

I just found this BAR manual that specifies that tactically, 3 to 5 round bursts are to be used (p. 186) and a total rate of fire of 120 to 150 rounds per minute (p. 161), about the same as the MG42:


RATE OF FIRE.-The automatic rifleman fires at the rate of fire most effective under existing conditions and generally at a rate of from 120 to 150 shots per minute automatic fire.
Click to expand...

By comparison, the air-cooled, heavy-barrel M1919A4 machine gun is expected to fire 60 rounds per minute for up to 30 minutes:


2. COOLING SYSTEM. The machine gun, caliber .30 M1919A4, is provided with a heavy barrel which is exposed to the air. This factor serves to keep the gun at operating temperatures under normal conditions, i.e., at the rate of about 60 rounds per minute for about 30 minutes.
Click to expand...

Regards,

Henning (HoHun)
 
Hi Scott,

Scott Kenny said:
You'll note that the MG3 has a much lower rate of fire than the MG42.
Click to expand...

It's worth noting that with the MG 3, the Bundeswehr did not acquire on of the rate-of-fire reduced variants that were available under the MG 42/59 name. Rate of fire on the MG 3 was indeed slightly reduced compared to the original MG 42, but I am not sure that was a deliberate design choice as the bolt carrier group had some improvements that apparently increased mass a little.

As the Bundeswehr certainly had institutional knowledge of the German WW2 experience, I believe that would indicate they didn't consider the high rate of fire an issue.

Regards,

Henning (HoHun)
 
Hi,

Colonial-Marine said:
I believe the concept behind the German focus on very high rates of fire for their infantry MGs was that in normal circumstances enemy infantry would only be exposed for brief periods of time. So, when you catch them in the open you want to send as much fire as possible downrange before they can move into cover.
Click to expand...

I'd say it can be confirmed from the regulation "HDv 240 Schießvorschrift für Gewehr (Karabiner), leichtes Maschinengewehr, Pistole usw.", though this still applies to the lMG and predates the universal MG concept of the MG34/MG42.

Paragraph 256 states that the most rapid fire which still allows careful aim is to be used with all weapons, not only to hit the enemy when he's briefly out in the open, but also for the shooters not to pose a target for too long themselves.

Paragraph 260 (the first paragraph dealing with the actual firefight) states that machine gunners and riflemen can not engage in long firefights. The ideal is to strike surprisingly in a "fire raid", rapidly firing a high number of well-aimed shots in a brief period until the intended goal of the fire raid is achieved, and to go into full cover immediately afterwards (and potentially re-locate to prepared alternate firing positions).

Paragraphs 261 to 264 deal with target selection and expenditure of ammunition. It's clearly the top priority topic of marksmanship training. Paragraphs 268 and 269 are titled "fire discipline" and also address this topic.

Colonial-Marine said:
There is some logic to this, but penalties that come with that high rate of fire. In intense combat green troops must be likely to fire excessive amounts of ammunition and ruin barrels.
Click to expand...

I would guess that having a crew-served weapon operating under the supervision of an NCO who can be expected to explicitely order a specific target to be engaged with a definite number of rounds, this would not be terribly likely to be a widespread problem. Consider that all riflemen are trained as machine gunners, so if any gunner starts wasting ammunition, he'll probably find himself swapping roles with the assistant gunner, some other rifleman or the NCO himself within a very short time. The German infantry always drilled fire discipline into their soldiers, going back at least the Prussians with their Dreyse breech loaders, and while I'm really not an expert for infantry combat in any way, I really doubt their grunts would screw up badly enough to turn the MG42 from an asset into a liability on a regular basis. Sounds a bit like "Its bark is worse than its bite" ... ;-)

View: https://youtu.be/LcpR77N2Jn4?t=499


Regards,

Henning (HoHun)
 
HoHun said:
I'm really not an expert for infantry combat in any way, I really doubt their grunts would screw up badly enough to turn the MG42 from an asset into a liability on a regular basis
Click to expand...
Expect that we DO have German WW2 AARs from all the branches of that military that list complaints of the MG42 rate of fire causing logestical issues from as early as 1942 when the thing was tested.

They couldn't keep the things fed even fire discipline before the German militry everything turn to shit.

Theres a reason why 550 to 900 rpm is consider the current sweet spot for ground weapons.

fast enough to fill an area of a target with lead but still slow enough to conserve ammo.
 
Hi,

Firefinder said:
Expect that we DO have German WW2 AARs from all the branches of that military that list complaints of the MG42 rate of fire causing logestical issues from as early as 1942 when the thing was tested.
Click to expand...

As I admit that I'm quite clueless about infantry combat, I'd certainly love to learn more about these.

The effective rate of fire isn't directly tied to the cyclic rate of fire, which on the MG42 was indeed unusually high. However, just like the Allied light machine guns, the MG42 was to be fired in short bursts (different from what is shown in the American WW2 clip I linked above).

Here's a summary of the rates of fire of the MG42 compared to the Allied machine guns I found data for (and to the older German lMG):

- MG42: 120 to 160 rounds per minute
- lMG: 120 to 160 rounds per minute (in bursts of 3 to 8 rounds) - both lMG 08/15 and MG13 are illustrated in the source
- Bren gun: 120 rounds per minute
- BAR: 120 to 150 rounds per minute
- M1919A4: 60 rounds per minute (for up to 30 minutes ... slightly different role)

If there were logistical issues with the MG42, there would have been the same logistical issues with the other machine gun types, as the effective rates of fire were all very similar when they were used as intended.

So, I'm curious what the concerns of the German AARs were ... :)

Regards,

Henning (HoHun)
 
Hi,

mirco1961 said:
bar 120 rounds per minute, changing 6 magazines?
Click to expand...

120 to 150 rounds per minute, even. That's how the BAR was to be used in combat, according to paragraph 178 in this manual:


A soldier was expected to take a loaded magazine out of a belt pouch and inserted it into the gun in 2 to 4 seconds, according to the manual.

One of the firing exercises in the manual gives the shooter 65 seconds to go through 6 magazines loaded with 5 rounds each, fired off in a single burst each. That's indeed 6 magazines in just over a minute, albeit with only 30 rounds fired.

Regards,

Henning (HoHun)
 
HoHun said:
.... Consider that all riflemen are trained as machine gunners, so if any gunner starts wasting ammunition, he'll probably find himself swapping roles with ....

Regards,

Henning (HoHun)
Click to expand...
In a perfectly-trained peace-time army yes.
But late in the war when you are reduced to a few wet-behind-the-ears conscripts, all bets are off. Who knows if they can fire their own weapon accurately, much less their buddy's weapon.
 
Hi Rob,

riggerrob said:
In a perfectly-trained peace-time army yes.
But late in the war when you are reduced to a few wet-behind-the-ears conscripts, all bets are off. Who knows if they can fire their own weapon accurately, much less their buddy's weapon.
Click to expand...

Being reduced to a few wet-behind-the-ears conscripts late in the war, the war is actually lost regardless of what machine gun these conscripts fail to employ properly ;-)

Naturally, to get the optimum from any weapon, good training is required. However, the necessity to restrict fire to short bursts and to observe firing discipline is emphasized in the BAR manual I linked just as it's in the German training manual, so I really see no reason to assume that poorly trained gunners would be any worse off with the MG42 than they would be with the BAR.

I'm actually hoping Firefinder is going to shed some light on this with some details from the German documents he mentioned, as it seems difficult to get to the bottom of this issue with fictional scenarios alone.

Regards,

Henning (HoHun)
 
An issue in considering the sustained rate of fire is whether or not the gun comes with a quick change barrel. The Bren and MG42 did, the BAR didn't (though the Belgian FN Mle D did). That was most important for the MG42 because it also covered the HMG role, it wasn't simply a squad MG, it had to compete with the Vickers and the M1919 in the sustained fire role. But it was also important for the Bren because the barrel needed changing after every 10 magazines, which is only 2 minutes 30 seconds at the sustained rate of 120rpm. IOW the BAR might have a sustained rate of 120 rpm, but for how long?
 
HoHun said:
Hi Rob,



Being reduced to a few wet-behind-the-ears conscripts late in the war, the war is actually lost regardless of what machine gun these conscripts fail to employ properly ;-) ......

Regards,

Henning (HoHun)
Click to expand...
Are you referring to the Black Watch Regiment of Canada during the spring of 1945?
They suffered 350 percent casualties between D-Day and VE Day. The supply of recruits from Canada had pretty much dried up. They were scraping the bottom of the barrel for cooks and clerks and drivers.
 
Hi Rob,

riggerrob said:
Are you referring to the Black Watch Regiment of Canada during the spring of 1945?
They suffered 350 percent casualties between D-Day and VE Day. The supply of recruits from Canada had pretty much dried up. They were scraping the bottom of the barrel for cooks and clerks and drivers.
Click to expand...

Actually, I didn't know that Canada was short on manpower, too - I was thinking of the late-war Wehrmacht, which ended up sending barely-trained, underage recruits into combat. Thanks for pointing that out, it connects to a statement by a British tank commander I recently read ... they were always short on supporting infantry. I didn't recognize the depth of the problem before!

Regards,

Henning (HoHun)
 
Hi DWG,

DWG said:
An issue in considering the sustained rate of fire is whether or not the gun comes with a quick change barrel. The Bren and MG42 did, the BAR didn't (though the Belgian FN Mle D did). That was most important for the MG42 because it also covered the HMG role, it wasn't simply a squad MG, it had to compete with the Vickers and the M1919 in the sustained fire role. But it was also important for the Bren because the barrel needed changing after every 10 magazines, which is only 2 minutes 30 seconds at the sustained rate of 120rpm. IOW the BAR might have a sustained rate of 120 rpm, but for how long?
Click to expand...

Good point!

For perspective, the German rates of fire are actually stated in the style of "a shooter should be able to fire X to Y rounds in 30 seconds", and with the tactical background envisioned as short "fire raids" before retreating into full cover and immediately re-deploying into a (prepared) alternate position, I think they probably weren't expected to keep firing until the barrel needed changing. I guess the idea might have been to change the barrel so when they started firing from that alternate position, they could do so with a cool barrel.

(The German term "Feuerüberfall" is sort of difficult to translate, maybe "assault by fire" would be better, but as in a military sense, an assault is associated with taking ground, I decided to call it a "fire raid". If there's a better term I'm not aware of, please let me know!)

Looking at ammunition expenditure in way, I think it's implied that a "fire raid" takes 60 to 80 rounds, regardless of the gun used, as this figure is also given by the 1937 manual written with the lMG 08/15 and MG13 in mind, which had a much lower rate of fire.

Regards,

Henning (HoHun)
 
Hi again,

While not directly relevant to the RPM question, I'm confident the chapter on the MG42 in Col. Chinn's "The Machine Gun" provides some useful general technical information on the weapon:

archive.org

The Machine Gun Volume 1 By George M Chinn : Free Download, Borrow, and Streaming : Internet Archive

712 pg of the master of Machine Guns detailed design and technical specs on dozens of designs. must have reference
archive.org

Other volumes of his work are also available for download here:

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org archive.org

Regards,

Henning (HoHun)
 
HoHun said:
For perspective, the German rates of fire are actually stated in the style of "a shooter should be able to fire X to Y rounds in 30 seconds", and with the tactical background envisioned as short "fire raids" before retreating into full cover and immediately re-deploying into a (prepared) alternate position, I think they probably weren't expected to keep firing until the barrel needed changing. I guess the idea might have been to change the barrel so when they started firing from that alternate position, they could do so with a cool barrel.
Click to expand...
I'd expect so. Especially with MG42s, where you can dump and change the barrel in 10-15seconds.
 
Hi again,

HoHun said:
The British expected 120 rounds per minute from the Bren gun:

Click to expand...

I just stumbled upon this "British Muzzle Loaders" video, showing the source for the "4 magazines per minute" rate of fire for the Bren gun (link timestamped to 2065 seconds):

View: https://youtu.be/LHY7jKU-WIk?t=2065


(As in practice, Bren gun magazines were only loaded to 28 rounds, that came down to 112 rounds per minute, but that's a very minor difference.)

Differing from what's stated in the Wikipedia, British Muzzle Loaders quotes the burst length to be used with rapid fire as 5 - 7 rounds. Not quite sure what's going on there, but as Wikipedia references a 1939 edition of "Pamphlet No. 4, Light Machine Gun, Small Arms Training, Vol 1, War Office" and British Muzzle Loaders in another version shows the title page of the 1942 edition of the same pamphlet, it might be a change stemming from combat experience:

View: https://youtu.be/ATYlngqA0oU?t=2511


(Of course, it also could be a simple or a mix-up of low and rapid fire burst lengths by the Wikipedia authors, but the 1942 cover actually mentions including amendmends to the 1939 edition, so the new edition wasn't just a reprint of the old, but must have had some actual changes.)

Regards,

Henning (HoHun)
 
German WW2 army machineguns had a high rate of fire requirement mostly for air defence.The near-uselessness of MGs for that purpose was not understood till about the introduction of the MG42, which coincides with many Il-2 definitive version aircraft showing up at the front.

The reasoning about lethality and psychology of high rof in infantry combat was made up ex post.

Today a lightened bold (increased rof) MG3 may have a comeback in remotrly controlled weapon stations on AFVs for C-UAS (shooting down drones) within 300+ m range.
 
Hi,

lastdingo said:
German WW2 army machineguns had a high rate of fire requirement mostly for air defence.The near-uselessness of MGs for that purpose was not understood till about the introduction of the MG42, which coincides with many Il-2 definitive version aircraft showing up at the front.

The reasoning about lethality and psychology of high rof in infantry combat was made up ex post.
Click to expand...

That's an interesting consideration, and I'd love to learn more about this. However, I believe it's not entirely consistent with the choice of a very high rate of fire by the Bundeswehr, who were aware of the WW2 experience and could have picked MG3 variants with a lower rate of fire, but didn't.

I share your doubts about the psychological effect being much of a factor, but with regard to lethality, it's worth noting that the tactics which benefit from a high rate of fire predate the MG34/MG42, as pointed out here:

HoHun said:
I'd say it can be confirmed from the regulation "HDv 240 Schießvorschrift für Gewehr (Karabiner), leichtes Maschinengewehr, Pistole usw.", though this still applies to the lMG and predates the universal MG concept of the MG34/MG42.

Paragraph 256 states that the most rapid fire which still allows careful aim is to be used with all weapons, not only to hit the enemy when he's briefly out in the open, but also for the shooters not to pose a target for too long themselves.

Paragraph 260 (the first paragraph dealing with the actual firefight) states that machine gunners and riflemen can not engage in long firefights. The ideal is to strike surprisingly in a "fire raid", rapidly firing a high number of well-aimed shots in a brief period until the intended goal of the fire raid is achieved, and to go into full cover immediately afterwards (and potentially re-locate to prepared alternate firing positions).
Click to expand...

Since these tactics were cast into Wehrmacht regulations long before the MG42 was developed, I don't believe they can be seen as post-fact rationalization of the MG42's high rate of fire.

Regards,

Henning (HoHun)
 
Well, the MG3 has a lower rate of fire than the MG42 and the Austrian post-WW2 machinegun on MG42 basis has only 850 to 900 rpm.

The MG45 (even higher rof than MG45, but not produced) is more of a counterargument, but its higher rof was probably a product of the weight reduction.
 
Hi,

lastdingo said:
Well, the MG3 has a lower rate of fire than the MG42 and the Austrian post-WW2 machinegun on MG42 basis has only 850 to 900 rpm.
Click to expand...

Actually, the 1960 edition of the "Taschenbuch für Wehrausbildung" reproducing Bundeswehr regulations lists the NATO-calibre MG 42 variant used back then with 1200 rpm, and the 1986 edition lists the MG 3 with the same 1200 rpm. (The current Bundeswehr website lists 1300 rpm, but that's what you'd expect from Public Relations! ;-)

I don't have contemporary German regulations on the MG 42, as my pre-WW2 marksmanship booklet predates the MG 42, but the Wikipedia value is "900 - 1500 rpm", with 1200 rpm considered average.

As the post-war MG 42 variants seem to have had improvements to the bolt which as a side effect increased mass, I suspect the possible drop from 1500 to 1200 rpm hadn't actually been a military requirement.

That was a drop by merely 20% though, which I don't think could be seen as a doctrinal change even if it had been a primary design goal.

The overall context would be roughly (arbitrarily rounded to 100s of rpm):

- Bren Gun: 500 rpm
- BAR: 600 rpm
- MG 75: 900 rpm
- Bundeswehr MG 3: 1200 rpm
- Bundeswehr MG 42 (7.62 mm): 1200 rpm
- Wehrmacht MG 42 (7.92 mm): 1500 rpm

Regards,

Henning (HoHun)
 
lastdingo said:
The MG45 (even higher rof than MG45, but not produced) is more of a counterargument, but its higher rof was probably a product of the weight reduction.
Click to expand...
Agreed. Many of the M2 .50cals on the civilian market are actually aircraft guns with ground barrels installed, which gives them a much higher ROF than a true M2HB ground gun (about 600rpm versus 450). The A/N M2 aircraft bolt is something like half the weight of the ground gun's bolt, partially for weight in general and partially because of the higher ROF.
 
Hi Scott,

Scott Kenny said:
Agreed. Many of the M2 .50cals on the civilian market are actually aircraft guns with ground barrels installed, which gives them a much higher ROF than a true M2HB ground gun (about 600rpm versus 450). The A/N M2 aircraft bolt is something like half the weight of the ground gun's bolt, partially for weight in general and partially because of the higher ROF.
Click to expand...

That's interesting, I hadn't been aware of that. In WW2, the US military was actually sort of unhappy with the aircraft version of the M2 because longer bursts (or more frequent bursts) would heat up the barrels to the point where the lining was destroyed and the gun became grossly inaccurate. That was more of a problem when strafing than in air combat, but it was serious enough for the US Navy to declare at the 1944 Joint Fighter Conference that they preferred 20 mm cannon for this very reason.

I really wonder why, if the problem was acknowledged, they didn't switch to the heavy barrel. It seems the weight difference was only ca. 10 kg per gun - not trivial, but considering that the US fighters carried a lot of ammunition, reducing the ammunition supply by 75 rounds per gun would have kept the weight constant and, by allowing rapid fire with no negative impact on accuracy or barrel life, might have been the overall better choice.

At least, that's what I'd speculate. This doesn't seem to be a very well-documented topic, unfortunately.

Regards,

Henning (HoHun)
 
Even if you use chromium/borium compounds you will always run into the heat problems associated with higher rates of fire which will always become unsustainable.
 
Hi,

Foo Fighter said:
Even if you use chromium/borium compounds you will always run into the heat problems associated with higher rates of fire which will always become unsustainable.
Click to expand...

Agreed, but I don't think that the capability for sustained fire would actually be necessary.

Here's a video on USAAF machine gun burst lengths and practical rate of fires, showing that with the aircraft version of the M2, a burst of 50 rounds would damage the barrel and reduce both muzzle velocity and accuracy (from the channel "WW II US Bombers", timestamped to 116 seconds):

View: https://youtu.be/VtiB7z94Uro?t=116


Later in the video, it's also pointed out that the sustained rate of fire in the case of the B-29 was limited to 30 rounds per minute, with 40 rounds per minute being permissible in emergency cases.

The video also shows a table with continuous firing limits which considers "cook-offs" (rounds being inadvertently fired due to the primer self-ignition caused by heat transfer from the overheated barrel), and for most burst lengths, the limit is 30 rpm or lower.

What I'd speculate is that the heavy barrel would at least allow a longer initial burst (or a greater number of short initial bursts) due to its higher mass absorbing more heat before reaching a dangerous temperature. I think you're probably right that it wouldn't make much of a difference once the heavy barrel has reached the critical temperature, if that's what you'd consider the "sustainable" case.

There might be a good reason the heavy barrel didn't make it into aircraft, but I've never found this mentioned anywhere.

From the "USN Report of Joint Fighter Conference NAS Patuxent River", quoted via Tony Williams:

"In addition to that you have one more great advantage - that is you can have longer and more frequent bursts without damage to the gun with the 20 than you can have from the .50 cal. That is important for the strafing airplane, because they are burning up their barrels and ruining their guns on one flight. Sometimes it is long before that one flight is over. They will come down with screaming barrels and get trigger happy, and then all the barrels are gone in one flight. It should not happen in a 20mm. Of course, you have disadvantages. You have a heavier installation, one-half as much ammunition for the same weight. Our standard ammunition in the Navy is 400 rounds in one gun. The Fleet has set up 30 seconds of fire as a minimum requirement for the .50 cal gun. We can't do that with the 20, so we give them 200 rounds. The 20 is lethal enough to get far more results out of that 200 rounds than the .50 ever will out of 400 rounds."
Click to expand...

That sounds as if the Navy was ready to change something about their fighter armament. I find it somewhat surprising that they didn't try the heavy barrel on the M2 .50 cal, but again, maybe they had a good reason I am simply unaware of! :)

Regards,

Henning (HoHun)
 
The heaviest barrel I came into contact with was on the renaging gun on Chieftain prior to the trial and use of the laser designator which, doubled as a weather detector.

In rain the range report could be as little as 2m prior to correcting the prism orientation and a second logic button.

Our Browning RG had a receiver at 42Lbs and a barrel at 30 Lbs weight and due to being limited to three round bursts, never saw a single burn out. I did see some talk about ribbed barrels being better for heat dissipation a la "Nambu" and some european LMG's.

We asked about more ammo to task the weapon against soft skin vehicles, three rounds into engine or drivetrain is sufficient to ruin anyone's day but we were ticked off for even suggesting it.

Great fun back in the day.
 

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