# Why was the Gast gun never used in aircraft during WWII?



## ShVAK (Sep 19, 2012)

It seemed like a perfect weapon for AA applications. 








Good rate of fire (Model 1917 from WWI was capable of 1600+ RPM from two barrels), mechanically reliable and had built in redundancy (if one side of the siamesed pair had a malfunction the other side would keep going). Also considering many cannons that were not spinner-mounted were paired, a set of Gast 20mm or even .50/12.7mm in each wing would make a good amount of sense. 

From Wiki: 
_
Gast demonstrated the weapon to ordnance experts in August 1917, who were so impressed that a production order for 3,000 guns was awarded to Vorwerk und Companie,[1] along with ten ammunition drums and spare parts for each gun at a unit price of 6,800 marks each. Delivery of the first 100 guns was promised for 1 June 1918, with production ramping up to 500 guns per month by September 1918.

Production of the weapon exceeded these initial projections, and the weapons were received favourably with promises of an order for a further 6,000 guns being promised in September 1918.
However, the gun was not widely used, and their existence was kept secret until three years after the Armistice; it was not until 1921 that the Allied Control Commission became aware of the Gast gun when a cache of 25 of the guns, ammunition and designs was found near Königsberg.[1] Gast himself had applied for a US Patent in 1920, which was issued in 1923.

A Gast gun was evaluated by the US Army, and found to be reliable and mechanically practical. _

Since the U.S. was aware of the Gast's existence and even tested a working version of it, this weapon had great potential on both sides of the conflict. It surprises me that no one actually deployed it after 1918 even in an anti-infantry role. Maybe too bulky? However as a mounted weapon this would have been less of a problem. 

Further adding to the "why not?" question, the Soviets were obviously impressed by the design enough to manufacture the Gryazev-Shipunov GSh-23, a belt fed Gast-based autocannon, for many of their fighters, bombers, and helicopters throughout the Cold War period in lieu of far more complex Gatling designs that NATO favored. 

Can't help but feel like someone missed the boat on this.

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## Jabberwocky (Sep 19, 2012)

Pinching a couple of direct quotes from Tony Williams:



> The Gast was actually a very big and heavy gun, with a couple of huge drum magazines. The MG81Z "twin" of WW2 was much faster-firing and much smaller and lighter, as well as being belt-fed.





> The Gast was thoroughly studied long before WW2, but no-one bothered to pick it up. I think that the problem may have been that it was too specialised. It couldn't be synchronised, and that was a major disadvantage at the time because most air forces preferred to use the same guns for fixed and flexible mounting (the British started out with the Browning and VGO, but rapidly dropped the latter)


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## ShVAK (Sep 19, 2012)

Both of those criticisms would seem to be less pertinent if mounted as a tailgun or in the wings. Soviet-designed Gast cannons were also belt fed, perhaps this required too much space in a WWII-era fighter wing? I know early H-S installations were a struggle in some fighters.


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## Shortround6 (Sep 20, 2012)

"Good rate of fire (Model 1917 from WWI was capable of 1600+ RPM from two barrels), mechanically reliable and had built in redundancy (if one side of the siamesed pair had a malfunction the other side would keep going). Also considering many cannons that were not spinner-mounted were paired, a set of Gast 20mm or even .50/12.7mm in each wing would make a good amount of sense. "

While 1600+ RPM from two barrels was very good for WW I it wasn't so good by even the 1930s. Browning could do 1100-1200rpm for a single barrel, Vickers was up to 900rpm for the old belt feed gun, German MG 15 was 1000-1100rpm. Russians managed up to 1800rpm from their MG. 

The guns were _NOT_ independent. they were interlinked, as one bolt moved back the other moved forward, the bolts were connected by a link that was pivoted in middle of the housing. If one gun jammed both barrels stop firing.


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## ShVAK (Sep 20, 2012)

Shortround6 said:


> While 1600+ RPM from two barrels was very good for WW I it wasn't so good by even the 1930s. Browning could do 1100-1200rpm for a single barrel, Vickers was up to 900rpm for the old belt feed gun, German MG 15 was 1000-1100rpm. Russians managed up to 1800rpm from their MG.
> 
> The guns were _NOT_ independent. they were interlinked, as one bolt moved back the other moved forward, the bolts were connected by a link that was pivoted in middle of the housing. If one gun jammed both barrels stop firing.



So you take the Gast design and modernize it accordingly. Lighter bolt for higher RPM, strengthened link, etc. Post-war Soviet Gast autocannons were capable of up to 3500 RPM, and that was with 23mm. I don't see why it wouldn't be possible to make a 20mm Gast with 2000+ RPM in WWII. 

Also I misread, one side of the mechanism was capable of _single_ shots if the other side jammed. That would be pretty useless in aerial combat. Maybe if there was a fail safe to disconnect the interlink if one side malfunctioned would allow the remaining gun to operate independently? I don't know the details of how that would work but it doesn't seem too far fetched.


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## davebender (Sep 20, 2012)

*MG151/20.*
42 kg
750 RPM
720 m/s

*GSh-23*
50 kg
3,500 RPM
715 m/s

Hmm. Small increase in weight gives you four times the rate of fire.

Another option the Luftwaffe rejected. However it's difficult to argue against the historical MG151/20 cannon which was lightweight, compact, reliable, effective and inexpensive to produce.


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## Shortround6 (Sep 20, 2012)

"Hmm. Small increase in weight gives you four times the rate of fire."

NS-23 37KG 550rpm 1944/45

NR-23 39KG 800-850rpm 1949

AM-23 43KG 1250rpm 1953-54

GSh-23 50 kg 3,500 RPM 1962-65? 

Hmm. 20 years gives you a much higher rate of fire. 

"historical MG151/20 cannon which was lightweight, compact, reliable, effective and inexpensive to produce."

Well 4 out of 5. inexpensive requires some good accounting techniques.


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## ShVAK (Sep 20, 2012)

There's also this beast.  Mounted on the Su-25 "Frogfoot." 

*Gryazev-Shipunov GSh-30-2*

Weight 115 kilograms (250 lb)
Length 2,044 millimetres (6.706 ft)
Caliber 30x165 mm
Barrels 2
Rate of fire 3000 rpm
Muzzle velocity 880 m/s (2,890 ft/s) to 890 m/s (2,920 ft/s)

A WWII 30mm Gast probably wouldn't have that rate of fire and/or would be heavier. But such a weapon would be a very viable and powerful option as a belly-mounted gun pod for Hs 129 in place of the BK 7.5 cm, I would think.


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## Shortround6 (Sep 20, 2012)

ShVAK said:


> A WWII 30mm Gast probably wouldn't have that rate of fire and/or would be heavier. But such a weapon would be a very viable and powerful option as a belly-mounted gun pod for Hs 129 in place of the BK 7.5 cm, I would think.



Both lower rate of fire and heavier, unless you think that the science of metallurgy made no advances in 20-30 years after WW II. 

And be careful what you ask for, you just might get it. 

30x165 mm ARSENAL Rounds

The Russian gun fires about a 20-22% heavier projectile about 3% faster than the 30mm gun the Hs 129 already used. Although the German AP round was closer in weight and had a higher velocity than the Russian gun. The rate of fire isn't very useful to the Hs 129. 100 rounds weigh about 84kg without links, the Hs 129 can't lift enough ammo to keep a 3000rpm gun feed for mare than a few seconds. One or two attack runs?


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## ShVAK (Sep 22, 2012)

Shortround6 said:


> The Russian gun fires about a 20-22% heavier projectile about 3% faster than the 30mm gun the Hs 129 already used. Although the German AP round was closer in weight and had a higher velocity than the Russian gun.



Which 30mm? The Hs 129 B-1 first received the Mk 101 (960 m/[email protected] RPM) and then the Mk 103 (940 m/[email protected] RPM w/ AP rounds) in the B-2. Both had significantly lower rates of fire than any Gast design would have even if we assume a greatly reduced capability compared to the more advanced GSh-30-2. You might be thinking of the Mk 108, which never saw service on the Hs 129. That had a much higher (650 RPM) rate of fire but nowhere near sufficient velocity to do much to a tank.


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## GrauGeist (Sep 22, 2012)

Also, a weapon with a high rate of fire might seem attractive, but consider that the higher the rate of fire, the more ammunition you have to have available...this means additional weight you have to carry aloft and additional space needed if you are going to have enough ammunition to last a certain amount of time.

In a perfect world, the Mk108s in the Me262 would have had 2,500 rounds and the B-17 would have been armed to the teeth with 20mm cannon instead of .50 cals...


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## ShVAK (Sep 22, 2012)

The Hs 129 also had twin 20mm MG 151 cannon and twin MG 131 13mm machine gun. Maybe you would have to ditch a couple of those for the Gast gun pod but all the heavier cannons it used historically suffered from relatively limited ammo (about 30 rounds in a Mk 101 pod, even less for the larger Bordkanone). The ideal mission profile was to bounce three or four tanks, strafe any soft or lightly armored targets with the 20mm/machine guns and then return to base, range was only about 420 miles so I imagine it didn't have a very long loiter time and it was slow and vulnerable anyway. 

Also worth mentioning that the empty space behind the Henschel's cockpit could be used to carry 3.7 or 7.5 cm rounds in an autoloading system, maybe that space could be utilized somehow for more 30mm ammo.


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## ShVAK (Sep 22, 2012)

Or setting aside the Hs 129, what about putting a 20 or 30mm Gast setup into a Schrage Muzik installation for night fighters?


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## Shortround6 (Sep 22, 2012)

ShVAK said:


> Which 30mm? The Hs 129 B-1 first received the Mk 101 (960 m/[email protected] RPM) and then the Mk 103 (940 m/[email protected] RPM w/ AP rounds) in the B-2. Both had significantly lower rates of fire than any Gast design would have even if we assume a greatly reduced capability compared to the more advanced GSh-30-2. You might be thinking of the Mk 108, which never saw service on the Hs 129. That had a much higher (650 RPM) rate of fire but nowhere near sufficient velocity to do much to a tank.



The 3% faster was in reverence to the muzzle velocity. The MK 103 used the same ammo (change of primer) as the MK 101 but the powder charged had to be lowered because the MK 103 could not take the strain, The AP round/s were left at the original ( MK 101) velocity. The Germans already had a more powerful cartridge than the one fired by the Russian gun. 

Firing more shells per second doesn't help as much for ground targets. They aren't moving like an airplane. A truck or tank doing 30mph can cover 88ft in 2 seconds, a 300mph airplane covers 880ft in 2 seconds.

High rates of fire help with the targeting problem. 

The later Hs 129s carried the MK 103 with a 100 round belt, about a 15 second supply. Even if your WW II Gast fires at a _mere_ 1200rpm you need about 400rounds for 15 seconds. The extra 300 rounds is a bit over 240kg. 

You have to be a bit careful when comparing gun weights. The British and Americans designed some of their guns to last over 10,000 rounds (barrels not included) the Russians often designed guns to last 2500rounds. This allowed for much lighter guns using the same quality steel and alloys. Both the Germans and Japanese had shortages of steel alloys that forced lower rates of fire to keep the strain down or lower powered cartridges than first used or both. Comparing a gun made in 1943 to one made in 1963 also ignores the knowledge in metal alloys and heat treatment gained in those 20 years that allow for lighter parts.

The original Gast weighed 60lbs. A 1919 Browning ground gun goes about 31lbs with a heavy barrel. The aircraft versions use a lighter barrel and by the early 30s can fire 1200rpm. even if you get the original Gast up to 2400rpm from 1600rpm what do you gain? 

"The ideal mission profile was to bounce three or four tanks" at 2-3 seconds per bounce? With the MK 101 gun (drum feed) that is 10 to 7.5 rounds per tank. With the MK 103 gun it is 33 to 25 rounds per tank. 

The MK 103 gun allowed for about 90% more firing time while firing over 50% more ammo per second. 


As far as the Schrage Muzik installation, what do you gain? If you want/need more firepower than a pair of MG/FF-MG 151-MK 108s then put in 3 guns or four. No new gun factory needed, no new parts system, no new training manuals and training schools for a new gun. 

We don't know what a German Gast, firing German ammunition and made of German materials would weigh. The Russians guns, both during WW II and after were much lighter than anybody else's guns of simialr ballistic performance and rate of fire.


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## ShVAK (Sep 22, 2012)

Shortround6 said:


> The original Gast weighed 60lbs. A 1919 Browning ground gun goes about 31lbs with a heavy barrel. The aircraft versions use a lighter barrel and by the early 30s can fire 1200rpm. even if you get the original Gast up to 2400rpm from 1600rpm what do you gain?



I see the Gast's advantages as applying more to heavy machine gun and cannons 20-30mm, as you said rifle-caliber machine guns weren't ever lacking for ROF even by the 1930's but during and after BoB they were largely useless against bombers and not even very good against fighters. Heavier arms were, but at higher rates of fire they suffered significant penalties in muzzle velocity like the Mk 108. This is where the Gast finds its niche--two slower-firing guns linked together gives you a similar or better rate of fire and coverage than one fast-firing cannon, but with theoretically better muzzle velocity, which equals better range and penetration. Perfect for interception, also perfect for defensive installations on bombers. 

You make good points with the Hs 129 and the S.M. that I concede. I'm freely making a lot of conjecture and speculation here, this is why I like to bring my ideas to places where there's a healthy bullsh-t filter.

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## Shortround6 (Sep 22, 2012)

"This is where the Gast finds its niche--two slower-firing guns linked together gives you a similar or better rate of fire and coverage than one fast-firing cannon, but with theoretically better muzzle velocity, which equals better range and penetration. Perfect for interception, also perfect for defensive installations on bombers."

The Gast is essentially two single guns linked together. Quite true, but it also means that it weighs as almost as much as two similar single guns. There is nothing in it's design that will significantly change the muzzle velocity ( beyond about 1% or less) of a given round fired from it. It may be simpler to build as the barrels do not move as in recoil operated guns and there is no gas system. It is essentially two blowback guns linked together. Weight of the two breech blocks and link resist the shell blowing back out the breech. Much like an Oerlikon resists bolt opening by weight of breech block assembly, spring and overcoming the forward inertia of the bolt. While the individual bolts of the Gast can be lighter than the bolts of two individual guns that is one of the major weight savings. 
You also have the problem that if one barrel has a misfire both barrels stop firing until the gun can be "charged". If one barrel suffers a feed malfunction both barrels stop firing. Assuming the feed malfunction doesn't foul the bolt your "single shot" capability comes from using a hand charger, electric solenoid, pneumatic cylinder or hydraulic cylinder to move the bolt after every shot. Useless for air to air combat and near useless for ground attack. 
The Russians may like them because they offer a good rate of fire from an easily manufactured gun. Given the Russian preference for almost "throw away" guns that give good performance for weight it may be understandable.


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## ShVAK (Sep 22, 2012)

Shortround6 said:


> The Gast is essentially two single guns linked together. Quite true, but it also means that it weighs as almost as much as two similar single guns. There is nothing in it's design that will significantly change the muzzle velocity ( beyond about 1% or less) of a given round fired from it.



Nothing inherent in the Gast design itself, but what about longer barrels? The Mk 108 was deficient in muzzle velocity because its high ROF mandated a short barrel to prevent misfires. Since a Gast is basically two guns just linked together, wouldn't two longer barrel guns at 400 RPM each be able to obtain a higher rate of fire than one Mk 108?


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## ShVAK (Sep 22, 2012)

Shortround6 said:


> You also have the problem that if one barrel has a misfire both barrels stop firing until the gun can be "charged". If one barrel suffers a feed malfunction both barrels stop firing. Assuming the feed malfunction doesn't foul the bolt your "single shot" capability comes from using a hand charger, electric solenoid, pneumatic cylinder or hydraulic cylinder to move the bolt after every shot. Useless for air to air combat and near useless for ground attack.
> The Russians may like them because they offer a good rate of fire from an easily manufactured gun. Given the Russian preference for almost "throw away" guns that give good performance for weight it may be understandable.



What if there was a way to unlock the link in the instance of a malfunction allowing each gun to operate independently?


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## stona (Sep 22, 2012)

ShVAK said:


> machine guns weren't ever lacking for ROF even by the 1930's but during and after BoB they were largely useless against bombers and not even very good against fighters.



The crews of the 424 bombers (excluding Ju 87s) lost between July and September 1940 as a result of enemy action,most being shot down by the RAF's fighters would probably disagree.

The crews of the 398 single engined and 214 twin engined Luftwaffe fighters lost to enemy action in the same period would also probably disagree.

The updating in 1935 of the fighter specification 37/34 requiring only four machine guns (in the wings) to specification 10/35 requiring six or eight was specifically to enable the fighters,eventually the Spitfire and Hurricane,to shoot down bombers. It was estimated that a fighter would only bring its guns to bear for about two seconds,hence the need for more guns to give any chance of scoring enough hits on the adversary.

More armour was added to almost all aircraft,fighters and bombers,as the war progressed and eventually rifle calibre machine guns did become much less effective.

Steve


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## ShVAK (Sep 22, 2012)

stona said:


> The crews of the 424 bombers (excluding Ju 87s) lost between July and September 1940 as a result of enemy action,most being shot down by the RAF's fighters would probably disagree.
> 
> The crews of the 398 single engined and 214 twin engined Luftwaffe fighters lost to enemy action in the same period would also probably disagree.



How many rounds did it take per target? Rifle-caliber machine guns were effective during BoB but only just, and it was still early in the war before everyone started up armoring their planes. And even then, many pilots on both sides of the BoB often cited the .303's as inadequate as a number of German planes were still able to return home even after being heavily shot up. Maybe not in LARGE numbers, but enough for the RAF to acknowledge cannon was needed.


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## Shortround6 (Sep 22, 2012)

ShVAK said:


> Nothing inherent in the Gast design itself, but what about longer barrels? The Mk 108 was deficient in muzzle velocity because its high ROF mandated a short barrel to prevent misfires. Since a Gast is basically two guns just linked together, wouldn't two guns at 400 RPM each be able to obtain a higher rate of fire than one Mk 108?



It wasn't misfires they were trying to stop, it was the cartridge case rupturing and letting high pressure gas back into the action of the gun. The short barrel allowed the shell to clear the muzzle sooner and drop the internal pressure as the bolt and case moved to the rear. A longer barrel would still have had the shell inside as the rear cartridge came out of the chamber and the higher pressure could have blown out the side of the case. Yes you could use a stronger spring, heavier breechblock(bolt) to slow down the bolt movement (rate of fire) to get better velocity. 
But again, the Gast is almost two complete guns, A Gast firing 30 X 82RB ammunition is going to weigh almost double what a single MK 108 did ( if built of the same materials and to the same standards) 




ShVAK said:


> What if there was a way to unlock the link in the instance of a malfunction allowing each gun to operate independently



For that to happen you need a main spring to drive the bolt forward. I don't believe the Gast used mainsprings. You also just cut the weight/mass of the bolt assembly in half meaning the bolt will accelerate much more quickly leading to early opening and the case ruptures mentioned above. 

Gas operated and recoil (moving barrel guns) used the gas/recoil system to operate a lock that delayed the opening of the bolt. Because they were not _depending_ on the weight of the bolt and the strength of the main spring for this delay their bolts could be lighter and move faster _once they had unlocked_.


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## stona (Sep 22, 2012)

An accurate two second burst from a Spitfire or Hurricane could deliver about 250 rounds on target.

There are always instances of heavily damaged aircraft returning home,just as one lucky shot could bring one down. 

The RAF had considered other armament at the same time as the eight .303 option. The then new 20mm Hispano-Suiza cannon was considered "supersensitive" to rigidity of mounting and difficult to mount in aeroplane wings. The RAF would only consider the cannon if 60 rounds per gun,in drums,could be fitted.

In 1938 Dowding wrote to Sholto-Douglas,clearly unimpressed with the cannon.

"There has been a lot of talk about the efficiency of the 20mm cannon and I have seen no proof that this gun will give decisive results.We ought to have carried out the most careful experiments to prove its value before we adopt it.If this was not done I shall wake up in a year's time and be told I am committed to having 15 squadrons of something with a 20mm cannon whereas I can tell you now I do not want any and so perhaps save a large sum of money."

It was not until early 1940 that Dowding was convinced by the 20mm cannon. No.19 Squadron was informed on 1st July 1940 that it was to be equipped with cannon armed Spitfires. They were a disaster,the cannon jamming for a variety of reasons. On 15th July Dowding wrote undiplomatically to the Air Ministry "Two cannon Spitfire unreliable."

The stop gap solution was the 2 cannon and 4 MG armed Spitfire. 

There were other problems too,maybe for another thread. As an example the first Spitfire IB to see action with 19 Squadron in October 1940 had to be flown at full power just to keep up with its machine gun armed counterparts.

It's another example of things not being as simple as they appear. "Just" mounting cannon in the wings of the Spitfire eventually led to a modification of the wing spar. 

Fighters armed with eight .303 machine guns shot down hundreds of aircraft in the summer of 1940 and that armament cannot therefore be described as "inneffective"

Cheers

Steve


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## 106rr (Mar 5, 2016)

Resurrecting an old thread here but the Gast Gun was used in WW2 aircraft. It was redesigned to fire .63 caliber cartridges. The ammo was loaded at Twin Cities Arsenal. They used a necked up 50 BMG cartridge case. The gun and ammo were designed for naval strafing and were supposed to penetrate the decks of enemy ships. 
The only application I could find was that they were put into B17s but only in the one South Pacific Squadron. The gun pod was fitted to the right side just aft of the cockpit. Images of the B17s from that squadron show only a blank cupola on the right side. The pictures may have been taken right before or right after the removal of the Gast Guns.
The only combat usage I could find was in the battle of the Coral Sea. As most of you know this battle was a mess. The Japanese fleet fired on one of its own ships when the convoy was steaming in a half circle. American aircraft then strafed their own American ships causing some casualties. 
The guns were removed and scrapped after one battle. The only official reason was that there were no personnel trained to maintain the system. All examples were scrapped. I hope that someone here has a sample cartridge. It will near the twin cities code on the base with a stab crimp primer pocket exactly like the base of the 50 BMG.

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