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.