Alternative airborne guns 2.0

[Shortround6]

But there is a catch. You always need some magazine even for the belt, that also has its weight, and drums were extremely convenient as self contained structural elements. The belt also has its non-zero mass. Therefore, the additional cost of the magazine mass in relation to the belt was much smaller.

You basically need a box. How strong the box is made may be a question. The Belt feed does not have spring forcing the rounds to the gun. The drum has to guide the rounds to the gun and keep them properly aligned. The belt needs just enough container to keep things pointed the same way while maneuvering, but pulling the belt helps (does not eliminate) small problems with alinement.
Try pushing a few dozen tapered pens along a table and see how well that goes
Granted the belt feeder/de-linker was about 8kg for the Hispano but the weight didn't change much, if any for long belts. Weight of links was certainly there.
Most magazine fed guns had covers/doors over the magazines so there may not be much savings in weight there.

Large magazines/drums soon got unwieldly.

 

[TM06]

I do wonder how the Breda 20/65 or Scotti 20/77 would've fared as a motorcannon - those Long Solothurn rounds hit very hard. They fitted a variant of the Breda on the Piaggio P.119, but information on that is scarce. Maybe fit it with a belt feed system, shorten the barrels (L/45~L/55?) and crank up the fire rate to a more reasonable level (600 RPM?). Italy having access to a powerful 20 mm cannon as early as ~1936 might radically change their later aircraft designs.

 

[Shortround6]

I do wonder how the Breda 20/65 or Scotti 20/77 would've fared as a motorcannon - those Long Solothurn rounds hit very hard. They fitted a variant of the Breda on the Piaggio P.119, but information on that is scarce. Maybe fit it with a belt feed system, shorten the barrels (L/45~L/55?) and crank up the fire rate to a more reasonable level (600 RPM?). Italy having access to a powerful 20 mm cannon as early as ~1936 might radically change their later aircraft designs.

Probably not well.
Trying to nearly triple the rate of fire is more than "cranking up" the rate of fire. It probably means a whole new mechanism.
The long Solothurn rounds are a bit deceptive. They aren't much more powerful than the Hispano. It depends on which particular type of ammo for either cartridge.
Feed system might be the easiest thing. Germans managed to hang a 100 round drum under the Flak 30 and have it feed into side where the box feed had been (a little more to it than that). That was the gun used in the He 112 that went to Spain.
Note that the Germans changed mechanisms when they went to the Flak 38 to get to 480rpm.

 

[peceed]

Modify the big Browning (scale it down) to fit the British .5 (12.7x81) cartridge like the Japanese did for the Ho-103. Yes it is going to need development work (time). It is not designing a new gun from scratch. You get a smaller (shorter), lighter (23kg?) gun that can fire faster (bolt has to travel a shorter distance).

The only justification for larger calibers in the early and mid-1930s was explosive ammunition. So why not create a BMG-sized cartridge with the largest possible explosive shells? The Americans had created an experimental 16mm cartridge during World War II, so it was feasible.
Adaptation of Browning should be done by changing the barrel and few minor details, and the new cartridge is a minor modification of the already used one.
In principle, doing both of these things is easier than adapting weapon to a new cartridge of changed length, and the benefits are much greater.
.6"-16 mm bullets would be an excellent alternative to .50 for anti-bomber use.
In a sense, this is transferring the conclusions regarding the ideal aircraft gun to the world of heavy machine guns.

 

[Shortround6]

The only justification for larger calibers in the early and mid-1930s was explosive ammunition. So why not create a BMG-sized cartridge with the largest possible explosive shells? The Americans had created an experimental 16mm cartridge during World War II, so it was feasible.
Adaptation of Browning should be done by changing the barrel and few minor details, and the new cartridge is a minor modification of the already used one.
In principle, doing both of these things is easier than adapting weapon to a new cartridge of changed length, and the benefits are much greater.
.6"-16 mm bullets would be an excellent alternative to .50 for anti-bomber use.
In a sense, this is transferring the conclusions regarding the ideal aircraft gun to the world of heavy machine guns.

It is possible. But not the best use of resources.

12.7 x 81 ammo.
The cost of the fuse is just about the same as the cost of a 20mm fuse (more material, nearly equal labor/machine time).
Now it is possible to take out the tracer element and expand the HE compartment to the rear, nearly doubling the HE content.
All the way from miniscule up to pathetic.
A 20mm tracer is going to hold around 3-5 times the amount of HE.
A 20mm HE round is going to hold around 5 times the amount of HE as a pure HE 12.7 round will.

Necking up to 15-16mm gets you a bit closer. The German 15mm HE/T held 2.8 grams of HE
Japanese Type 99-1 HE/T shell held 5 grams of HE. Plain HE shell held 10 grams.

If 20mm shells are not doing the job trying to use 12.7-16mm shells but a lot more of them is going to be very difficult.
Also note the AP round. trying to make twin or triple threat projectiles in small sizes pretty much means you don't do any job well.
There was a 12.7x81 AP round without the tracer, the core extended back into the tracer area and a heavier core of the same diameter traveling at the same speed is going to punch through more metal. Whatever filler (incendiary?) they had in the nose is pretty much a 'strikes on target' indicator.

 

[TM06]

Probably not well.
Trying to nearly triple the rate of fire is more than "cranking up" the rate of fire. It probably means a whole new mechanism.
The long Solothurn rounds are a bit deceptive. They aren't much more powerful than the Hispano. It depends on which particular type of ammo for either cartridge.
Feed system might be the easiest thing. Germans managed to hang a 100 round drum under the Flak 30 and have it feed into side where the box feed had been (a little more to it than that). That was the gun used in the He 112 that went to Spain.
Note that the Germans changed mechanisms when they went to the Flak 38 to get to 480rpm.

Au contraire my friend, a modified version of the Scotti 20/77 was fitted to the Semovente da 20/70 quadruplo, featuring a disintegrating belt link and reportedly had a rate of fire of 600 RPM per gun.
Source.
Although the quadruplo was completed in early 1943, it's entirely feasible that those modifications could be introduced much earlier.

 

[peceed]

Also note the AP round. trying to make twin or triple threat projectiles in small sizes pretty much means you don't do any job well.

It is a standard. Space for tracer is essentially free, required anyway to get a stable flight. The magnesium cap with incendiary is considered a payload but is also a free ballistic cap.

It is possible. But not the best use of resources. (...)

However, it was being done.
The alternative there is not a 12.7 mm vs. 20 mm, but 12.7 mm vs. 16 mm - essentially the strongest ammo for Browning M2 possible..

The cost of the fuse is just about the same as the cost of a 20mm fuse (more material, nearly equal labor/machine time).

However, it is not a dominant factor in the total cost.
Furthermore, a shell with 6 gram HE(I) has a ratio of filler to fuse cost similar to 20mm ammo commonly used during the war!
HEI/T is obsolete, the belt should be composed of API/T and HE(I) cartridges.

 

[peceed]

There was a 12.7x81 AP round without the tracer, the core extended back into the tracer area and a heavier core of the same diameter traveling at the same speed is going to punch through more metal.

Different shell types should have the same speed, but it implies that the round should be shorter to get the same mass.

 

[Shortround6]

Au contraire my friend, a modified version of the Scotti 20/77 was fitted to the Semovente da 20/70 quadruplo, featuring a disintegrating belt link and reportedly had a rate of fire of 600 RPM per gun.
Source.
Although the quadruplo was completed in early 1943, it's entirely feasible that those modifications could be introduced much earlier.

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.

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?

 

[z42]

Very close - in the case of ammunition, the design space is from 23x115 to 30x111. Mine shells are preferred because they can have better ballistics at practical distances while maintaining or even higher effectiveness against air targets.

With the same weight, shorter and wider shells are preferred because they provide more volume in the barrel, and thus better use of powder and a larger volume of the case.

There is one rule that everyone should know: there is no point in lengthening the cartridges (proportionally enlarging the case and the shell, maintaining ballistics), because the rate of fire of enlarged is inversely proportional to the length of the cartridges, so the mass of the second salvo does not increase, but the mass of the weapon so enlarged increases proportionally.

These rules have their common sense limitations - longer cartridges can be narrower and provide a greater number of shots,, it is worth using the entire length available in a typical wing to mount the weapon and the ammunition container. A larger caliber shell has a heavier front part and more wasted space by the ogive.
That's why the 20x138, 23x115 and 30x111/30x90 RB cartridges have almost the same total length!
It's worth reaching thresholds of destroying a target with a single projectile - for heavy bombers it was a mineshell with a 400 gram filling, for fighters it can be assumed that it is about 50g PETN with minor corrections for the size of the targets and hitting the wingtips.

I think the 30x113 used in the post war ADEN would have been a pretty good solution for WWII. 220g shell at 800 m/s, cartridge is fairly compact.

 

[z42]

You basically need a box. How strong the box is made may be a question. The Belt feed does not have spring forcing the rounds to the gun. The drum has to guide the rounds to the gun and keep them properly aligned. The belt needs just enough container to keep things pointed the same way while maneuvering, but pulling the belt helps (does not eliminate) small problems with alinement.
Try pushing a few dozen tapered pens along a table and see how well that goes
Granted the belt feeder/de-linker was about 8kg for the Hispano but the weight didn't change much, if any for long belts. Weight of links was certainly there.
Most magazine fed guns had covers/doors over the magazines so there may not be much savings in weight there.

Large magazines/drums soon got unwieldly.

Belts might be better than drums, but aren't an 'infinitely scalable' solution either. The longer the belt, the heavier it is, and has more friction pulling it. At some point the gun rips the links apart, alternatively isn't powerful enough to pull the belt. You can to an extent compensate with sturdier links, but then at some point the delinker will start to dent the cartridges instead.

All this becoming worse the faster you want to go through your belt.

The modern solution being various linkless feed systems, but those are somewhat heavy and complicated, and AFAIU a solidly post-WWII solution. Or maybe something like that would have been feasible already back then?

 

[Shortround6]

Belts might be better than drums, but aren't an 'infinitely scalable' solution either. The longer the belt, the heavier it is, and has more friction pulling it. At some point the gun rips the links apart, alternatively isn't powerful enough to pull the belt. You can to an extent compensate with sturdier links, but then at some point the delinker will start to dent the cartridges instead.

All this becoming worse the faster you want to go through your belt.

The modern solution being various linkless feed systems, but those are somewhat heavy and complicated, and AFAIU a solidly post-WWII solution. Or maybe something like that would have been feasible already back then?

It was done, at least in B-26s and P-51Ds. In the bombers moving heavy ammo from under the gunners feet up to the guns was a problem.
On the early US .50 cal (1940 and before) there were significant problems. At the same time they increased the rate of fire they changed the contour of the cam track that operated the feed pawls and doubled the weight of pull. (doubled the distance the gun could lift the same weight of belt).
In fighters very few (No?) aircraft moved the entire belt at one time.
Picture of model.

Only the top row is going to move. The 2nd row is going to be peeled back as the top row moves.
Wen the 2nd row is used up the 3rd row is going to start being lifted up and as it moves across the outside end of the 4th will be peel up.
The lower rows don't move until it is their turn.
In a snail drum all the rounds are moving and the spring/s have to be able to move the rounds through the friction.
In some bombers they used gravity to help feed the lower guns or tail guns. (sloped ammo tracks)

Edit, computer crashed about 5 times writing this post. Some stuff got lost.
The B-26 and P-51Ds (and other bombers?) used electric servo motors and sprockets to move the linked ammo through the feed ways.

 

[Shortround6]

I found this website with photos of a large variety of Italian and Hungarian 12.7 x 81 bullets.

12,7x81 Breda cutaways bullets

Do you happen to know the weight of the AP and API-T steel cores? 🙂

forum.cartridgecollectors.org

The long AP penetrators were 20.8 grams and the short one was 11.2grams.
US .50 cal used a 26.2 gram penetrator.

 

[peceed]

I think the 30x113 used in the post war ADEN would have been a pretty good solution for WWII. 220g shell at 800 m/s, cartridge is fairly compact.

This idea is quoted in the first post of the thread
But energy and momentum can be a little too big for wing installations - so 23 mm mineshell 50 kJ is probably better as an all-arounder.

 

[bf109xxl]

But energy and momentum can be a little too big for wing installations - so 23 mm mineshell 50 kJ is probably better as an all-arounder.

Hmmm, I think I've seen something like this already... No names/designations, just numbers: 0.2 kg x (700 m/s)^2/2 = ...

 

[peceed]

Hmmm, I think I've seen something like this already... No names/designations, just numbers: 0.2 kg x (700 m/s)^2/2 = ...

... = 0.175 kg * (750 m/s) ^ 2/2 (higher capacity shell)
= 0.135 kg * (850 m/s) ^ 2/2 (mineshell)

 

[Shortround6]

I am puzzled by people who think that something that was made to work in the early-mid 50s could have been made to work in the early-mid 40s if only they had had the idea.
We all KNOW there were no advances in metallurgy, metal working technology or advances in propellent technology in those 6-10 years, right.

The real shiny cases are the Japanese 30 x 92RB, 30 x 115 and the 30 x 122. Followed by the German 30 X 91RB and the 30 x 184B.
Please note that the 30 X 115 used a 235g shell at 700m/s.
Maybe the Americans/British/Germans could have done a bit better in WW II but you don't get 1950s ballistics in the 1940s.
Japanese 30 x 92RB shell went 264 grams and because it was NOT a 'mine' shell it held 29 grams of HE, Or about the same as the German 433 grams shell in the 30 x 184B round (later got the mine shell).

 

[bf109xxl]

... = 0.175 kg * (750 m/s) ^ 2/2 (higher capacity shell)
= 0.135 kg * (850 m/s) ^ 2/2 (mineshell)

By the way, it seemed to me that using a cartridge case from a 14.5 or 15mm cartridge for 23mm ammo just saves metal and space, but there is no point in mastering a new cartridge case if there is no production of 14.5/15mm ammo (only two countries had it, AFAIK), it is easier to take 20mm. Madsen rules.

 

[tomo pauk]

Maybe the Americans/British/Germans could have done a bit better in WW II but you don't get 1950s ballistics in the 1940s.

What should've been the ballistics of the 1950s, and for what calibre?

 

[tomo pauk]

In the book Geheimwaffen - 1939-1945 - Flugzeugbewaffnungen, it can be read that, by installing a bolt 3.7kg lighter than the standard on the MK 108, the rate of fire goes from 650 to 950 rd/min. If also the recoil buffer is installed, the RoF was supposed to go beyond 1200 rd/min(!!).
The same book notes that, with standard bolt (63 kg), the MK 112 was making 300 rd/min, while with ever lighter bolts, the RoF was going to 450 rd/min with the lightest, 42 kg bolt, and the weak point are now becoming the ammo links/belts.

(BTW - that book is now some 20-25% more expensive than a year ago)