Alternative airborne guns

[tomo pauk]

Idea is that we 'design' better guns for different airforces for 1937-1945. Guns for different purposes - fixed installations for fighters (predominantly for air-to-air combat), guns for defensive fire, anti-tank guns etc. Slight modification(s) of guns 'borrowed' from countries', whether freindly or not, also count. Alternative suggestions - 'plan B's - are also okay. Ideally, suggestions should've been based on operating principles known and feasible in the era. Ditto for improved ammo.

(we can do better than just suggesting the .50 BMG for Spitfires and Hurricanes of 1939-40)

 

[Glider]

I would like to see if the Russian 20mm ShVAK cannon fitted to the Hurricane in 1940. There is a temptation to say Spit as well but it might be difficult to fit it but the Hurricane had a good sized weapon bay and the ShVAK doesn't get the attention I believe it deserves. The same goes to the 12.7 mm version which in 1940 was well ahead of the 0.5M2 of the time.

 

[Shortround6]

It seem to take 4-6 years to get a new gun into production and sorted out.
Different countries had different standards of reliability and durability.

AT guns are a real can of worms. They rapidly get very big and almost need a plane designed around them.
Let's also remember that penetration of the armor does not by any means guarantee a dead tank. You have to damage what is behind the armor.
Small very fast projectiles can pierce armor but may need multiple hits to actual damage the tank (or crew) sufficient to take it out of action.

You also have the old problem of supply, limited factory space/workers so too many projects can screw things up.

 

[tomo pauk]

For the UK, USA and Germany:
A cannon based on the Oerlikon FF. 100 g shell fired at 700-ish m/s. Belt fed. One pair on early Hurricanes, Spitfires, Bf 109s, Fulmars, and fighter Blenheims. 2 pairs on Bf 110/Fw 187. Later 3 on Bf 109s, and 2 pairs on British fighter aircraft (incl NF Mosquito) + on early Fw 190s (outside the prop circle). 6 on Beaufighter, FB Mossies and German NFs.
Also as a turret gun.
2 pairs on P-40s, P-51s. 3 pairs on fighters with R-2800 and P-38.
By 1942-43, improve the RoF.

 

[Shortround6]

Not sure what you are gaining.
Unless you use a new type/form of shell construction you have severely compromised the payload of the shell.

When you go from 128-130 grams down to 100 grams you are just shortening the payload section. The fuse will be the same size and weight. As a point of information the British went from a brass fuse to an aluminum fuse post war and lightened the shell by 12-14 grams.
The rear of the shell cannot be modified as it needs to stand up to the firing stresses.
The shell walls cannot be made thinner for the same reason.
A 100 gram shell might only be 60% as destructive as the 130 gram shell from an explosive point of view.
German mine shell used a form of construction that the British and Americans either couldn't or wouldn't copy in over 5 years.
Short light projectiles also slow down quicker than the long heavy shell so the increase in velocity may not buy much, if anything, in effective range.

 

[tomo pauk]

Not sure what you are gaining.

Going for Oerlikon means saving a few years to get cannon armament for both UK and USA. Having cannons in service in the time of BoB is a major boon for the RAF FC.
For the USA, the reliability problems are gone since the rebated rim cartridges were headspaced at the bottom of case, rather than at the neck.

Unless you use a new type/form of shell construction you have severely compromised the payload of the shell.

When you go from 128-130 grams down to 100 grams you are just shortening the payload section. The fuse will be the same size and weight. As a point of information the British went from a brass fuse to an aluminum fuse post war and lightened the shell by 12-14 grams.
The rear of the shell cannot be modified as it needs to stand up to the firing stresses.
The shell walls cannot be made thinner for the same reason.
A 100 gram shell might only be 60% as destructive as the 130 gram shell from an explosive point of view.
German mine shell used a form of construction that the British and Americans either couldn't or wouldn't copy in over 5 years.
Short light projectiles also slow down quicker than the long heavy shell so the increase in velocity may not buy much, if anything, in effective range.

I am trying to improve hit probability due to increased MV, especially if the target requires substantial lead, as in the beam attack case. It also makes sense to fire both cannon(s) and MGs at such target.
The 'lowest' Oerlikon used 130 g shell - same as the more powerful 'L' and much more powerful 'S' types, so there is a substantial strength reserve for the low-powered FF gun. But, yes, reduction of destructive power for single shell will amount to at least 30%, even if the bottom of it is made of thinner material.
On the other side, we might look at big picture. A Spitfire with 4 such cannons will only pay the weight price worth 2 Hispano II cannons. It will do 2100-2200 rd/min, vs. 1200 rd/min for Hispanos. Or 21-22 kg of shells/min, vs. 15.5 kg/min. Or, the Bf 109F can have 3 cannons within the airframe vs. just one cannon, while not paying too hefty the weight price. Granted, the Germans will make a switch to the mine shell by mid-1940.

 

[tomo pauk]

A better M4 37mm cannon for the USA - it will be simple to improve MV, just don't use the heavy & long shell from the M1 AA gun as it was done historically (picture; 2nd from left is ammo for M4 & M10 cannons, 3nd from right is ammo for M1 and M9 cannons)

US artillery ammo manual
M4 37mm cannon manual

So instead of 1.34 lb shell, we'd be better off with a shorter (less metal content) shell of ~1lb weight, that will also allow for a bit more propellant - two things put together are bound to offer much better MV.

 

[tomo pauk]

Next-gen cannons for Luftwaffe:
- MG 151 is designed for the Madsen 23mm ammo (HE shell was with almost twice the explosive content of what was in the 20 mm M-shell) - sorta the 'German VJa-23)
- 'MK 105 - the 'mid power' 30mm cannon (330 g M-shell @ 700-750 m/s, 600-500 rpm), 90-100 kg

 

[Shortround6]

Going for Oerlikon means saving a few years to get cannon armament for both UK and USA. Having cannons in service in the time of BoB is a major boon for the RAF FC.
For the USA, the reliability problems are gone since the rebated rim cartridges were headspaced at the bottom of case, rather than at the neck.

The rebated rim cartridges were headspaced on the case mouth, bottle neck/shoulder or case taper. The rim did nothing nor could it do anything.



I am not sure the Oerlikon was as well developed in the early/mid 30s as you think, nor was it large production. Hispano got into the cannon business when Oerlikon could NOT supply guns fast enough for the French D 500/510. The Oerlikon guns at that time had firing rates of closer to 400rpm than 500rpm. The French Oerlikon (Hispano Type 7 and 9) FFS fired at 360-420rpm.

I am trying to improve hit probability due to increased MV, especially if the target requires substantial lead, as in the beam attack case. It also makes sense to fire both cannon(s) and MGs at such target.
The 'lowest' Oerlikon used 130 g shell - same as the more powerful 'L' and much more powerful 'S' types, so there is a substantial strength reserve for the low-powered FF gun. But, yes, reduction of destructive power for single shell will amount to at least 30%, even if the bottom of it is made of thinner material.

as I said before, all of the weight saving (or at least a great part of it) is going to come from shortening the body of the shell. Also note that short tracer projectiles are either going to have a short distance tracer or very little explosive.
As to the strength of the shells. A lot depends on the propellants used and the length of the barrels. It is possible that all three Oerlikon rounds used the same peak pressure.
By using a slower burning propellent they could use the same peak pressure and yet maintain higher pressures (than the short cartridge) further out the barrel and get higher velocity.
Projectile has to be built to withstand the peak pressure.

Also note in the drawing above, the 20mm X 110 RB Oerlikon headspaces on the shoulder.

Russian 20mm projectile.

You might do a bit better than that.
A 20mm Hispano projectile is about 40% longer than the Russian one in the drawing. A 100 gram projectile for the Oerlikon would be between the two.
Please note that the US and Britain used the same projectiles in the HIspano aircraft guns and the Oerlikon AA guns.
Britain had also rejected the Hispano FFS for aircraft use due to the use of greased ammunition.
I would note that the brass fuse used in WW II Hispano ammunition weighed about 27 grams.

 

[tomo pauk]

The rebated rim cartridges were headspaced on the case mouth, bottle neck/shoulder or case taper. The rim did nothing nor could it do anything.
The cartridges that headspace at the rear are the rimmed case (on the left) and belted case (on the right). Blet fits into recess at back of the chamber.

Also note in the drawing above, the 20mm X 110 RB Oerlikon headspaces on the shoulder.

There is no neck worth speaking about when it is about the FF or FF/M shells - see picture.
The driving band was of diameter or 20.9mm, the outside diameter of case mouth was 20mm, so the case mouth headspacing is also no-go. At any rate, the API mechanism that was applied in Oerlikon guns and their offsprings (MK 108, different Japanese cannon) was firing the shells before they breeech was fully closed.
The x110 shell have had a meaningful shoulder, unlike the shells used on the FF.

I am not sure the Oerlikon was as well developed in the early/mid 30s as you think, nor was it large production. Hispano got into the cannon business when Oerlikon could NOT supply guns fast enough for the French D 500/510. The Oerlikon guns at that time had firing rates of closer to 400rpm than 500rpm. The French Oerlikon (Hispano Type 7 and 9) FFS fired at 360-420rpm.

The big FFS fired at lower RoF than the smaller FFL, let alone the small FFF. Oerlikon cannons were in production in early 1930s, so there is enough of time for setting up the factory in UK, USA, or make a licencing deal like the Germans did for the FFF, or the French for the FFS.

as I said before, all of the weight saving (or at least a great part of it) is going to come from shortening the body of the shell. Also note that short tracer projectiles are either going to have a short distance tracer or very little explosive.
As to the strength of the shells. A lot depends on the propellants used and the length of the barrels. It is possible that all three Oerlikon rounds used the same peak pressure.
By using a slower burning propellent they could use the same peak pressure and yet maintain higher pressures (than the short cartridge) further out the barrel and get higher velocity.
Projectile has to be built to withstand the peak pressure.

Russian 20mm projectile.
View attachment 598608
You might do a bit better than that.
A 20mm Hispano projectile is about 40% longer than the Russian one in the drawing. A 100 gram projectile for the Oerlikon would be between the two.
Please note that the US and Britain used the same projectiles in the HIspano aircraft guns and the Oerlikon AA guns.
Britain had also rejected the Hispano FFS for aircraft use due to the use of greased ammunition.
I would note that the brass fuse used in WW II Hispano ammunition weighed about 27 grams.

Thank you.
My idea was, and still is, is that a) making a deal with Oerlikon about airborne guns both UK and USA can shave several years for their cannon-armed fighters to see wide service, and b) that installing two times of the FF derivatives vs. one FFS or Hispano can make up a lot of what one-to-one comparison might find lacking for the FF.

 

[tomo pauk]

For the Soviets (granted, their airborne guns were very good, it was their in-service aero engines that needed improvement)
- 'VJa 25' - shell taken from the 25mm AA piece, that uses necked-out 23mm case. Perhaps we can get the 275g shell to ~750 m/s, at 600 rd/min. One shell should ruin the day for anything 1-engined.
- 'Baby' 37mm cannon - not unlike the post-war N-37. A 735g shell at close to 700 m/s, ~250 rd/min, a ~120 kg weapon (the N-37 weighted even less, while making 400-450 rd/min). Should make less recoil-related problems than the powerful NS-37, and 1-shot the Ju 88 and the like.

Obviously, the 'baby 37' is for M-105 powered fighters and IL-2, plus perhaps for Pe-2. The 'VJa-25' for anything mass-produced from 1942 on.

 

[ThomasP]

Although it is in that in-between slot like the 15mm MG151, I always thought an aircraft variant of the 15mm Besa/Czech ZB-53 might have been worth pursuing (with or without an explosive round). It had a good MV (2700 ft/sec) and excellent ballistics (I think the standard AP round weighed ~1200 grains). The only problem was the low 450 rpm ROF (at least in the tank mounted variant) but that could have been increased if the 7.92mm variant is any indication (selectable at 450/800 rpm).

Also, a 20mm based on the .30/.50 cal M2 Browning might be nice. I have not been able to find any real reason why this could not have been done by the US if wanted. I believe the Japanese developed and fielded a 20mm aircraft cannon variant using the Browning action. Also, if I am not mistaken, the Browning action was used for the US 37mm AA gun, so use in a 20mm should not be a problem?

Or how about the UK finish development of the Vickers .5-inch 'D', lightened for aircraft use? Excellent MV (~3000 ft/sec) with excellent ballistics (boat-tailed 700 grain bullet) and a good range of ammo (Ball, AP, AP-T, and some type of Incendiary) by the mid-1930s, giving plenty of time for further development of both gun and ammo.

PS I have been told (anecdotally) that the Browning M2 action did not lend itself to use in a 20mm, but this makes no sense to me. Is anyone aware of an actual reason why this might be true?

 

[Shortround6]

Although it is in that in-between slot like the 15mm MG151, I always thought an aircraft variant of the 15mm Besa/Czech ZB-53 might have been worth pursuing (with or without an explosive round). It had a good MV (2700 ft/sec) and excellent ballistics (I think the standard AP round weighed ~1200 grains). The only problem was the low 450 rpm ROF (at leas in the tank mounted variant) but that could have been increased if the 7.92mm is any indication (selectable at 450/800 rpm).

Been over this one a few times. MV was actually higher, about 2900fps, but not much faster than the 20mm Hispano. Unfortunately the gun was actually about the same weight as a Hispano. Specs say 5kg heavier but specs for the Hispano often do not include either the drum or the belt deed mechanism. So we can spend a lot of time and effort trying to get the gun up to the same rate of fire as the Hispano, for no practical difference in MV, a much lighter shell weight and not much difference in installed weight.
If you have that kind of extra engineering capacity get the MK V Hispano into production sooner.

Also, a 20mm based on the .30/.50 cal M2 Browning might be nice. I have not been able to find any real reason why this could not have been done by the US if wanted. I believe the Japanese developed and fielded a 20mm aircraft cannon variant using the Browning action.

Possible, the US certainly spent plenty of money and effort on a raft of experimental guns and cartridges during WW II that went nowhere.
The Japanese Ho-5 cannon was sort of a scaled up Browning. But the overall length of the cartridge was not a lot longer., The HEI projectile used by this gun was the lightest 20mm HE projectile (79 grams) used by anybody in a 20mm gun. The 20mm Hispano cartridge was longer and about 60% more powerful in terms of ME. You could scale the Browning up and it would probable work but don't think you are going to get a lightweight, high rate of fire gun with a powerful cartridge without an awful lot of work, if ever.

Or how about the UK finish development of the Vickers .5-inch 'D', lightened for aircraft use?. Excellent MV (~3000 ft/sec) with excellent ballistics (boat-tailed 700 grain bullet) and a good range of ammo (Ball, AP, AP-T, and some type of Incendiary) by the mid-1930s, giving plenty of time for further development.

The Vickers ,5 inch "D" used a cartridge case 120mm long or 21% longer than the US .50 cal. granted the over length difference wasn't quite so great.

See: Untitled Document

The gun was slow firing (and you had quite distance for the bolt to travel on each shot) and these high velocity guns shot out their barrels fairly quickly.

Quote from the website above
"The gun barrel was water-cooled as usual and rate of fire was 350-450 rpm. Gun weight was 101 lbs (46 kg), or 122 lbs with water (55.3 kg) and it was noticeably longer than the compact Class B, with a barrel length of 45 inches (114 cm) and an overall length of nearly six feet (179 cm). "

Makes the Hispano look really, really good

 

[ThomasP]

Hey Shortround6,

Thanks for the info.

re the Vickers, I did say ". . . finish development of the Vickers .5-inch 'D', lightened for aircraft use?".

In all seriousness, I think the US should have pursued a 20mm version of the Browning. There is no reason a developed version could not have had ballistics at least as good as the Oerlikon variants. Plus that might have (hopefully) avoided the problems the US had with the Hispano.

 

[Shortround6]

in reverse.

Plus that might have (hopefully) avoided the problems the US had with the Hispano.

US had two problems with the Hispano.
1. because of it's caliber it was classified as a cannon and not a machine gun or small arm and looser tolerances were permitted on all parts. Until that is changed any 20mm full auto cannon firing at anywhere near 600rpm is going to have problems.
2. The US was woking from French drawings (the US did License the Hispano, not copy the British version) and did not incorporate the changes the British made until way late in the program. Like the shorter chamber. There was a lot of finger pointing going on between the ammo makers and gun makers as to where the fault was, Would a different design of gun have stopped that? I believe the US was fooling around with greased ammo to make the gun work while the British had rejected the Oerlikon for aircraft use because of greased ammo.

There is no reason a developed version could not have had ballistics at least as good as the Oerlikon variants.

Rather depends on the cartridge used. But a Browning scaled up to take the 20mm Hispano cartridge (and shell) is going to be a bigger, heavier gun than the Ho-5. You don't get 50% more kinetic energy out of a gun for free.

re the Vickers,I did say ". . . finish development of the Vickers .5-inch 'D', lightened for aircraft use

Well, you have to lighten it by almost 40lbs to get it to the weight of the US. 50 cal. then you have to increase the rate of fire to even reach the rate of fire of a 1930s Browning, and if you cut the barrel you loose velocity.

In all fairness on the last the Vickers "D" was getting 3000fps velocity when the US. 50 cal was getting 2500fps. Better propellent in the late 30s allowed for the increase in velocity of the US .50 and the Vickers "D" never got the new propellent. Without new propellent the Vickers "D" is going to burn barrels at an incredible rate in an air cooled version.

 

[ThomasP]

Hey Shortround6,

re:"US had two problems with the Hispano. . . ."

I can say from experience reworking blueprints (by hand) from metric to English and/or from 1st angle to 3rd angle projection, that although doing so would/should have incurred a delay in production (I would have to have a set of blueprints to give you any estimate of how long), it should in no way have reduced the reliability of the first weapons off the production line. (I have never read that there was any particular reliability issue with the French guns?) Pre-production testing should have caught the problems. If this had anything to do with the poor reliability, it was due to incompetence on the part of the engineers and/or supervisory personnel.

As to the difference in spec between machine gun and cannon, this is again an example of incompetence on the part of the engineers and /or supervisory personnel - a competent engineer would have looked at the specs the French used and realized that they should be used until it was proven that looser tolerances (or whatever other changes were made) did/would not effect the weapon's performance. And again, that is what pre-production testing is for.

I believe that the US had production examples of both the French and the British made guns long before production began - so that needs to be factored in as well.

Competent people do not order a complex system into production without being sure it works to an acceptable degree. And with a complete set of functional blueprints and physical examples of the working system . . . there is really no reasonable excuse. (Unless there were no competent people available to do the job? Not being snarky here, it is a very real possibility though I do not think it was the case.)

 

[Shortround6]

The first reason is often given, I don't know if it was true.

I will note that over 30,000 early production guns that had been placed in storage were later reworked into the M3 20mm cannon (sort of an American Hispano MK V) so they couldn't have been too bad or were easily modified.

at any rate see; Modifications and Attempts at Standardization

 

[ThomasP]

Hey Shortround6,

Thanks for the link. Interesting read.

So, if I am reading it right, the main problem was the chamber length (a problem which should have been caught in pre-production testing) and the fact that it would have taken too much work to fix it (since it would have needed a new barrel or serious rework of some parts of the receiver or some such) and therefore 40,000+ unreliable weapons were produced, or were suspect enough that they were not issued. Eeeek!

FWIW, I might buy the war-time pressure for why they were not reworked immediately, but I still have to conclude that the initial gearing up was done incompetently.

Does anyone have specific information on the reliability of the guns in the early vs the later installations. The reason I ask is that I do not remember reading anything about reliability issues for the early guns themselves, as fitted to the P-38 or P-400/P-39D-1. I do remember reading about the belt pull in the P-38s being inadequate at first, but I do not think what I read included any reasons why.

 

[Admiral Beez]

Or how about the UK finish development of the Vickers .5-inch 'D', lightened for aircraft use? Excellent MV (~3000 ft/sec) with excellent ballistics (boat-tailed 700 grain bullet) and a good range of ammo (Ball, AP, AP-T, and some type of Incendiary) by the mid-1930s, giving plenty of time for further development of both gun and ammo.

I have a vision of a Fairey Swordfish with a single Vickers .5 inch on the centreline torpedo mount, angled downward below the spinner. Once available we'll swap this out for single 40mm like on the Hurricane. Take that U-Boats.

 

[fastmongrel]

A .50 cal machine gun might just about scratch the paint on a submarine. A 40mm S Gun is going to leave some nasty scratches maybe even some dents.