Alternative airborne guns 2.0

[Shortround6]

Ignoring propellant (because I'm too lazy to look up data and take that into account), the same shell momentum as the Mk 108 is reached with a 255g shell at 700 m/s. So maybe something in that ballpark?

Propellent to velocity doesn't work that way. If you want a certain energy (not momentum) you have to put the energy in and that is in the form of propellent.

MK-108 with 330g shell had 42,100 joules of energy. Which is less than a 20mm Hispano.
The Soviet 23 x 115 fired a 184g shell at 700m/s and had 45,000 joules.
Japanese Ho-155 30 x 115 shell fired it's 235g shell at 700m/s and had 57,600 joules. just under a 37% increase in energy.
British Aden 3M LV 30 x 86 fired a 273g shell at 604m/s and had 49,800 joules. 18.3% increase in energy.
Case length does not tell you a lot about powder capacity as you don't know how far down the shell goes into the case and how thick the rear of the case is.
Rear end of case will vary a little bit. But adding 20% to case length can really change the actual propellent space in short cartridges.

As a basic rule of thumb if you want 10% more velocity you need 20-21% more propellent. 20% more velocity needs around 44% more propellent and 40% more velocity needs somewhere in the 90% range.
Cutting bullet/shell weight only goes so far.

Now you have to get the cartridges to play well in the barrels you want to use. Pressure curves, Breech staying sealed up long enough and so on.

 

[z42]

Propellent to velocity doesn't work that way. If you want a certain energy (not momentum) you have to put the energy in and that is in the form of propellent.

I was trying to estimate the recoil impulse, not calculate the muzzle energy. But, as mentioned, I didn't take into account the momentum of the propellant gasses.

 

[bf109xxl]

The Soviet 23 x 115 fired a 184g shell at 700m/s and had 45,000 joules.

200g, 690 m/s -> 47.6kJ
175g, 740m/s -> ~48kJ

 

[peceed]

For some time now I have been convinced that explosive projectiles built like rod warheads in missiles would work very well. A 10 cm rod with a diameter of 2 mm weighs 2.5 g. Assuming an efficiency of 80%, about 100 grams of rods are needed to create a circle with a diameter of one meter and 200 grams for a diameter of two meters, which allows us to think about guillotining a fighter with a heavy 20 mm projectile. A 2 mm rod is able to cut the aluminum structure of the airframe and the skin. Thanks to the perpendicular velocity vectors, the energy of the explosion would be added to the kinetic energy of the rods in a uniform way, cutting a cone out of the target. Thanks to the progressive movement of the projectile, the cutting length would be greater than the diameter of the unrolled rods alone. The ammunition will be particularly dangerous in the case of fire from aircraft (from directions close to the aircraft axis).

 

[TM06]

I would like to see some documentation or photos of the belt feed.
In English sources I have seen mentions of the Breda modified to to fire at 600rpm. A refence for "A" 20mm Scotti experimental gun that could fire at 600rpm and Scotti experimented with guns firing 20 x 70RB, 20 x 110 Scotti and 20 X 138B.
The Scotti 20/70 mod 38, mod 39 and mod 41 is certainly a possibility but there is certainly room for confusion.
Pictures of the quad mount do not help. The guns are tilted to the right a considerable degree which means the that feed is high and the ejection port is low. A strange way to arrange a belt feed. Extra curvature of the feed way? Perhaps they were looking for gravity assist to get the empties out?
No mention is made of modifying the guns to feed both left and right handed.
The guns are arranged in line vertically, unlike the US quad .50 where the guns are staggered.
View attachment 804056
So the belts/ammo boxes do not interfere with each other.
German Quad 20mm had the guns lined up.
Not actual proof but it does make me curious.
I would note that the tilted guns would appear to offer clearance for the standard feed trays to be inserted from the left with the lower right gun having the tray inserted down between the two top guns?
Again not proof but the layout is strange for belt feed guns.
The Breda M35 is supposed to have been modified to belt feed starting in 1937 and evolved into mod 41 with a rate of fire of 600rpm and using L/70 barrels.
Or there was a lot of confusion going on?

It's not perfect and there's definitely room for error here, but War Thunder has a detailed 3D model of the Quadruplo which has the belts visible:

Spoiler: 3D model

From what I can glean, the gun only seems to feed from the left side.
The mechanism seems relatively compact given the small size of the turret, and this specific armament layout would probably be highly effective for a defensive armament on bombers. Speaking of bombers, there were a few that were planned to fit the Scotti 20/77 - the Piaggio P.133 and CANT Z.511 Idrogigante are the first that come to mind.

 

[Shortround6]

It's not perfect and there's definitely room for error here, but War Thunder has a detailed 3D model of the Quadruplo which has the belts visible:

It is a video game.
In the link you posted earlier
Source.
There is a picture of the 4 gun mount on a display mount. Without feeds which does not help a lot, but some.

However video game vs the photo does bring up a few more questions.
Guns pivot in elevation in front of the feeds, sources vary from -5 degrees +90 degrees to -10 degrees +85 degrees.
Even a 90 degree pivot (change in elevation) means a major change in the feed system. US quad 50 had the belt boxes pivot with the guns. Granted other power mounts did not but they used flexible articulated feed chutes. Not as artistically pleasing as the naked belts in the video game?
If they had used feed chutes at least the right hand feeds would have been shielded from empty casings and links being showered on them from the ejection ports of the left hand guns.
Given the placement of the trunnions the lower belts either have a heck of an S bend and/or they a feeding a breech that is well forward of the trunnion and ammo feed boxes.

Perhaps the lower guns use feed chutes and the upper guns do not? Or you have the upper belt running over/rubbing against the lower belt at low elevations?

Given the photos I don't even know how they aimed this thing.
The quad gun on the display appears to use a typical AA sight (or space for one) on a large bracket coming back from a center point on the frame attached to the trunnions.
Pictures of the vehicle and the Video game do not show this bracket and do not show any visible sight or bracket.
There is no room at the rear of the turret for the gunner. He could be on one side or the other but there is still is no sight.
can't link photo.
Kind of shows the problem with belt feeds. The range of motion that the feeds need.
It has been done but it needs a lot more than putting some belt boxes in the bottom of the turret and modifying the gun feed system/s.
What they planned to wind up with may have been rather different from the two prototype vehicles they built. A lot more work from the "proof of concept" vehicles.

 

[Shortround6]

Soviet 23 X 115 ammo can turn into a rat's nest due to post war production.
2003-2004 Jane's Ammunition Handbook shows 10 different countries manufacturing it with 34(?) loadings (some duplicates).

They can range from 173 grams (Pakistan) to 200 grams (Soviet AP-I BZ) and velocities can range from 690m/s to 740m/s
Soviets loaded the AP-I to 740?
Some countries only loaded the 175g shells to 690m/s. But this is almost 60 years after the end of WW II.
And there were 6 soviet guns and 3 Chinese ones using the ammo so some countries might not have been pushing things to limit?
The NS guns used the 175g shells at 690m/s (?) and some of the later guns got up loaded ammo?

 

[bf109xxl]

They can range from 173 grams (Pakistan) to 200 grams (Soviet AP-I BZ) and velocities can range from 690m/s to 740m/s

The Soviets had only two sets of ammo - the initial (since 1944 to 1953) and the improved (since 1953) ones. Weights of the AP-I and HE-I shells were the same in both cases - ~200 and ~175 g correspondingly.
The major difference between the sets was the design of the fuze.

Soviets loaded the AP-I to 740?

And HE-I as well - since 1953. And only for NR-/NS-23, whereas a value of 705 was indicated for the AM-23.

Some countries only loaded the 175g shells to 690m/s. But this is almost 60 years after the end of WW II.

Undoubtedly, there was some variation in values due to different gun designs.

And there were 6 soviet guns and 3 Chinese ones using the ammo so some countries might not have been pushing things to limit?

I suppose, only NS-23 ammo are relevant within the scope of discussion.

The NS guns used the 175g shells at 690m/s (?) and some of the later guns got up loaded ammo?

The NS-/NR-23 used both ammo sets (OZT/BZ ~200g, 690m/s, since 1953 - OFZ/BZ-A 175g, 740m/s), the AM-23 used only the later ammo set (OFZ/BZ-A 175g, 705m/s).
BZ, BZ-A == AP-I
OZT == Fragmentation-I + Tracer
OFZ == HE-I

 

[TM06]

It is a video game.
In the link you posted earlier
Source.
There is a picture of the 4 gun mount on a display mount. Without feeds which does not help a lot, but some.

However video game vs the photo does bring up a few more questions.
Guns pivot in elevation in front of the feeds, sources vary from -5 degrees +90 degrees to -10 degrees +85 degrees.
Even a 90 degree pivot (change in elevation) means a major change in the feed system. US quad 50 had the belt boxes pivot with the guns. Granted other power mounts did not but they used flexible articulated feed chutes. Not as artistically pleasing as the naked belts in the video game?
If they had used feed chutes at least the right hand feeds would have been shielded from empty casings and links being showered on them from the ejection ports of the left hand guns.
Given the placement of the trunnions the lower belts either have a heck of an S bend and/or they a feeding a breech that is well forward of the trunnion and ammo feed boxes.

Perhaps the lower guns use feed chutes and the upper guns do not? Or you have the upper belt running over/rubbing against the lower belt at low elevations?

Given the photos I don't even know how they aimed this thing.
The quad gun on the display appears to use a typical AA sight (or space for one) on a large bracket coming back from a center point on the frame attached to the trunnions.
Pictures of the vehicle and the Video game do not show this bracket and do not show any visible sight or bracket.
There is no room at the rear of the turret for the gunner. He could be on one side or the other but there is still is no sight.
can't link photo.
Kind of shows the problem with belt feeds. The range of motion that the feeds need.
It has been done but it needs a lot more than putting some belt boxes in the bottom of the turret and modifying the gun feed system/s.
What they planned to wind up with may have been rather different from the two prototype vehicles they built. A lot more work from the "proof of concept" vehicles.

Your apprehension towards the model is understandable, but I think War Thunder gets a pass here - their vehicle models (especially the WW2 ones) are extremely detailed and based almost exclusively on reliable sources for the vehicles, sometimes down to the blueprints. There's also the War Thunder forums which are a goldmine for good sources.
But I digress.
I brought up the Quadruplo because it shows that a belt-fed Scotti 20/77 or Breda 20/65 with a fire rate of ~600 rpm is possible, which would make them fairly attractive offensive/defensive armaments for the Regia Aeronautica. Like I said before, the guns were fitted (or planned to be fitted) on certain aircraft - the CANT Z.511 and Piaggio P.133 for the Scotti and the Piaggio P.119 for the Breda.

 

[tomo pauk]

Oerlikon FF for everyone?
- USA - Can have the cannon in service much earlier than it was the case (holds true for most/all countries mentioned here). Avoids the Hispano debacle, since the API working principle is not susceptible for the chamber length being off by a razor-thin difference. Light weight means that there is no need for more than 4 weapons on a fighter. The MV is/was low, so a lighter shell (~100 g?) combined with a bit hotter loading can help (also for the other countries). Three on a P-39, 2-4 on a P-40, P-51 and Wildcat, 4 on the P-38, P-47 and the big Navy fighters. Belt-fed and big-drum versions should be no brainer early on, as well as the slight RoF upgrade by mid-war (again, also for the others).
- UK - 2-4 on the Mk.1 Hurricanes, Spitfires and Fulmars, later 4 on the fighters, even 6 on the Mossie FB and Beaufighter. Can do an even warmer welcome to the LW for the BoB. Also applicable for Canada and Australia.
- Germany, Japan - earlier introduction of a big drum/box and/or belt feed.
- Italy - they can have a much better firepower early on. Both Japan and Italy (but not just them) can give the M-shell idea a try.

 

[z42]

Oerlikon FF for everyone?
- USA - Can have the cannon in service much earlier than it was the case (holds true for most/all countries mentioned here). Avoids the Hispano debacle, since the API working principle is not susceptible for the chamber length being off by a razor-thin difference. Light weight means that there is no need for more than 4 weapons on a fighter. The MV is/was low, so a lighter shell (~100 g?) combined with a bit hotter loading can help (also for the other countries). Three on a P-39, 2-4 on a P-40, P-51 and Wildcat, 4 on the P-38, P-47 and the big Navy fighters. Belt-fed and big-drum versions should be no brainer early on, as well as the slight RoF upgrade by mid-war (again, also for the others).
- UK - 2-4 on the Mk.1 Hurricanes, Spitfires and Fulmars, later 4 on the fighters, even 6 on the Mossie FB and Beaufighter. Can do an even warmer welcome to the LW for the BoB. Also applicable for Canada and Australia.
- Germany, Japan - earlier introduction of a big drum/box and/or belt feed.
- Italy - they can have a much better firepower early on. Both Japan and Italy (but not just them) can give the M-shell idea a try.

I'm not a huge fan of blowback based guns as a principle of operation, but if you want a reliable auto-cannon at the start of WWII, the Oerlikon FF family is one of the very few contenders. I'd pick the FFL for a bit more MV.

 

[tomo pauk]

I'd pick the FFL for a bit more MV.

The main advantage of the FF(F) - it's small size - was probably of no interest for the USA, UK, Italy and japan since their fighters were all of more generous proportions than the Bf 109. So yes, I agree that the FFL is a very strong contender; it is also Tony Williams' favorite

I'm not a huge fan of blowback based guns as a principle of operation,

The 'short Solothurn' round might just be the ticket here - not overpowered (140g projectile at 740 m/s), so the gun designed around it will still be of modest proportions, unlike the gun designed around it's big brother that was comparable with the big Oerlikon, the 'S' family.

 

[Shortround6]

The Oerlikon needed a bit of sorting out. So did the Hispano but that is hindsight.
Turned out the Hispano needed greased or at least waxed ammunition. Improvements in grease/wax helped late war guns. As did heating to keep them functioning at higher altitudes (like over 15,000ft).
The Allied Oerlikon guns (naval service) required grease also, this was well known even the 1930s and was one reason that some air forces didn't like it. Problems with cold air at altitude.
Now look at where it was used, like Japan and the Pacific.
Allies had a lot trouble with Oerlikons on artic convoys, despite needing less maintenance than the Hispano gun in general.
France liked the idea that the Hispano could fire at 700rpm. Turns out the Hispano didn't like to fire at 700rpm (it broke).

There was a lot of who knew what, when going on. And you needed 2-3 years to go from decision to even small scale production.

Germans spent a lot of time working with the Oerlikon gun. It does not seem to be quite as ready to go out of the box as it seems.

 

[tomo pauk]

The Oerlikon needed a bit of sorting out. So did the Hispano but that is hindsight.
Turned out the Hispano needed greased or at least waxed ammunition. Improvements in grease/wax helped late war guns. As did heating to keep them functioning at higher altitudes (like over 15,000ft).
The Allied Oerlikon guns (naval service) required grease also, this was well known even the 1930s and was one reason that some air forces didn't like it. Problems with cold air at altitude.
Now look at where it was used, like Japan and the Pacific.
Allies had a lot trouble with Oerlikons on artic convoys, despite needing less maintenance than the Hispano gun in general.

There was no ideal weapons back then. All of them needed heating in the wing installations, and that includes the machine-guns.
Having the weapons very close to the engine and it's kilowatts and kilowatts of heating was of the great help, and probably one of reasons why the cowl guns were very popular, even in 1945.

There was a lot of who knew what, when going on. And you needed 2-3 years to go from decision to even small scale production.

Germans spent a lot of time working with the Oerlikon gun. It does not seem to be quite as ready to go out of the box as it seems.

If there was a problem of this or that nature with a weapon, having the actual examples years in advance helps with debugging them. A far better situation than with trying to debug the weapons during a shoting war, while also trying to improve them, and make them in many, many thousands.

French were sending the Oerlikon-armed fighters in Zurich aero meeting in 1937 (bad as these fighters were).

 

[MikeMeech]

In order not to clutter the 'P-39 mondial' thread, here is a thread about the alternative guns of 1935-45. To spice it up - let's say that the historical heavier guns are exception, while the new norm should be the alternative guns at your liking. So - the Hispano cannon is merely a footnote, Germans don't buy the MG FF, Soviets make a faster move away from the Shvak, Italians make something else besides the Breda LMG and HMG etc.
Anything between 7mm and 60mm is in the play, to deal with the suitable targets in the air and on surface, with extra points for coming out with the gun(s) that can actually fit on the existing aircraft, especially on the 1-engined fighters of the day.
Extra points also for keeping the guns simple, on the tech level of that decade.

Hi
RAF publication AIR 41-82 SD737 'Armament Volume II, Guns, Gunsights, Turrets, Ammunition and Pyrotechnics' published in 1954 (Freely available online on the RAF Air Historical Branch website), has mention of the various calibres discussed for use on aeroplanes during 1919-1930, from .28 inch to 37 mm, what actually happened before a 'what if?' can be useful:

Chapter 4 covers the 20-mm Hispano Gun, Chapter 6 Feed Mechanisms for 20-mm Guns and Chapter 19 Ammunition. Other chapters are on different guns, gunsights, turrets etc. So well worth the download.

Mike