Were the 15*69B cartridge a better option for early WWII fighters

[stoxm73]

I have not found the data for this cartridge yet.

However, its project should share the same shape and weight with its two big brothers, which according to Williams' website is about 57 grams.

If this cartridge had the similar kinetic energy with the American 0.50, then it would have a muzzle velocity around 750 m/s. Besides, its weight might allow it accommodate 3 gram of burst charge in normal HE, or 10 gram in minengeschosspatrone.

The whole cartridge might be a bit shorter than American 0.50, and easily be chambered into M2 or UB. If it could reach 800 RPM, it dwarfed most of the contemporary guns.

It is very surprising why German never put it into use?

 

[Shortround6]

Without further information everything is speculation.
Unless there is a typo. Germans used the 15 X 96 cartridge without belt.
Using only a 69mm cartridge length does not give enough powder capacity unless there is a lot of bottle neck (very fat case).

If you want the kinetic energy of the US .50 cal you have generate the energy by using a similar amount of propellent.
Maybe not identical but you don't get something for nothing. Using a smaller case capacity and heavier bullet/projectile can get a bit better efficiency
but trying to drive 57 Gram projectiles at 750mps is not going to be easy.
The 12.7 X 81 ammo drove 33-35grams bullets at about 750mps. Driving bullets that are about 60% heavier at the same speed is going to call for around 60% more propellent.

A pictures/drawings of the 15 X 69B cartridge?

Edit.
Propellent weights for a few cartridges.
13 X 64 = 7.1 grams
12.7 X 81 = 9.2 grams
12.7 X 99 = 15.6 grams
15 X 96 = 24.5 grams.

 

[stoxm73]

Without further information everything is speculation.
Unless there is a typo. Germans used the 15 X 96 cartridge without belt.
Using only a 69mm cartridge length does not give enough powder capacity unless there is a lot of bottle neck (very fat case).

View attachment 770282
If you want the kinetic energy of the US .50 cal you have generate the energy by using a similar amount of propellent.
Maybe not identical but you don't get something for nothing. Using a smaller case capacity and heavier bullet/projectile can get a bit better efficiency
but trying to drive 57 Gram projectiles at 750mps is not going to be easy.
The 12.7 X 81 ammo drove 33-35grams bullets at about 750mps. Driving bullets that are about 60% heavier at the same speed is going to call for around 60% more propellent.

A pictures/drawings of the 15 X 69B cartridge?

Edit.
Propellent weights for a few cartridges.
13 X 64 = 7.1 grams
12.7 X 81 = 9.2 grams
12.7 X 99 = 15.6 grams
15 X 96 = 24.5 grams.

The 15 X 69B is the only one missing the project in the following picture. The 15 X 83B is its big brother with a 57 gram project and a MV of 870 m/s. Both figure and data are from Williams' website.

 

[tomo pauk]

It is very surprising why German never put it into use?

When the cartridge was in development?

On a constructive side:

Were the 15*69B cartridge a better option for early WWII fighters

German early ww2 (1st 20 months of ww2?) airborne guns were with several shortcomings - the LMGs were weak-ish (like all LMGs), and the MG FF was without the belt feed, limited to 60 rd drums for too long. The shortcomings affected both fighters and bombers. The two guns (MG 17 and MG FF) were also with different MVs, so the trajectories didn't match - again not a good thing if the pilot on a fighter tries for a high G shot.
MG 151/15 was better from the MV and feed standpoint, yet it was not to be had before 1941, and was not an easy fit as a bomber defensive gun. It will also not fit in the wings of the Bf 109 without some wing surgery.

Having a belt-fed heavy MG (that is perhaps 60% the size and weight of the MG 151/15) improves their overall firepower. Especially if the heavy MG can fire shells, small as they are.

 

[z42]

Larger than "traditional" HMG (~ .50 cal) but smaller than 20mm might be in some kind of uncanny valley?

• If you shoot slugs, you make slightly bigger holes than a HMG, but, probably not worth it compared to mounting more traditional HMG's for the same weight and shooting more bullets and hopefully hit something important.
• If you shoot shells, the fuse takes takes up as much volume as for a larger shell, leaving relatively less space for the actual explosive. You end up shooting shells that are as complicated and expensive as a larger shell, but with much less oomph.

I'm sure all of the WWII combatants would have loved to have a high velocity, high rpm, reliable, and decently lightweight autocannon from the get-go. But alas, for various reasons it wasn't to be.

 

[Shortround6]

Having a belt-fed heavy MG (that is perhaps 60% the size and weight of the MG 151/15) improves their overall firepower. Especially if the heavy MG can fire shells, small as they are.

things do not scale well. If you increase caliber the general rule of thumb is to cube things.
But then come all the exceptions. Nobody scaled the US .50 cal or Soviet 12.7 up. A US 12.7mm scaled up to 20mm would use a 174 gram projectile.
Just using liner measurements the case would be 156mm long and about 26.6mm in diameter.
Most 20mm cannon are closer to a scaled up 12.7 X 81 cartridge.
Now a Japanese Ho-103 gun was about 22kg or about 3kg lighter than a 60% MG 151.
A lot depends on the cartridge. 12.7 X 81 necked up to 15mm and the gun lengthened a bit hold the shell?
Use the 15 x 69b case several years early to keep the overall cartridge length down?
Is the short case going to do what you want with the propellants of 1939/40 or do you need 1944 propellants and pressures ?

You might be able to build a Ho-103 equivalent using a short 15mm round but I think the velocity is going to be a lot closer to 600m/s than to 750M/S.

 

[tomo pauk]

Now a Japanese Ho-103 gun was about 22kg or about 3kg lighter than a 60% MG 151.
A lot depends on the cartridge. 12.7 X 81 necked up to 15mm and the gun lengthened a bit hold the shell?
Use the 15 x 69b case several years early to keep the overall cartridge length down?
Is the short case going to do what you want with the propellants of 1939/40 or do you need 1944 propellants and pressures ?

You might be able to build a Ho-103 equivalent using a short 15mm round but I think the velocity is going to be a lot closer to 600m/s than to 750M/S.

Ho 103 is too light. The ammo it uses is of the too low power, much better to use the Belgian/French 13mm round as a starting point. Even the US or Soviet 12.7mm is better bet. 13mm TuF, too.
As for the weapon base, I'd rather use something that weights about 27-28 kg:
- weight of a MG FFM with belt feed motor?
- or, sorta 3/4 of a Ho-5
- or, a B-20 cannon that fires lighter shells
- or, Browning HMG, with barrel for 15mm ammo

Granted, Germans need this in mass production by the time ww2 starts, in order to have their aircraft outfitted with these guns.

 

[tomo pauk]

I'm sure all of the WWII combatants would have loved to have a high velocity, high rpm, reliable, and decently lightweight autocannon from the get-go. But alas, for various reasons it wasn't to be.

Thing was that perfect weapons were too late, and many of belligerents started the war with weapons that were either woo weak (sometimes and somewhat countered by installing a lot of them, but also many times it was one or two pairs of LMG on a fighter), or with too slow MV, or with low RoF, or were unreliable, or a fighter might fit just one of them. Or a combination.

Back to the Germans, having a powerful enough HMG, that is belt-fed, with decent MV and RoF (the OP is realistic here with suggesting moderate MV and RoF) would've been a benefit when looking at what they fielded in the 1st 2-3 war years on their A/C - fighters, bombers and attackers.

 

[z42]

Thing was that perfect weapons were too late, and many of belligerents started the war with weapons that were either woo weak (sometimes and somewhat countered by installing a lot of them, but also many times it was one or two pairs of LMG on a fighter), or with too slow MV, or with low RoF, or were unreliable, or a fighter might fit just one of them. Or a combination.

Yes, that was what I was hinting at with my previous comment. Reasons varied, but the bottom line being that nobody really entered WWII with a good autocannon, even though many had recognized the advantages of it. E.g. the British had come to the conclusion that they wanted to jump straight from the .303 to 20mm already several years before the war started (1934 or 1935 IIRC?), but for various reasons their autocannon of choice wasn't ready by the time hostilities broke out.

Back to the Germans, having a powerful enough HMG, that is belt-fed, with decent MV and RoF (the OP is realistic here with suggesting moderate MV and RoF) would've been a benefit when looking at what they fielded in the 1st 2-3 war years on their A/C - fighters, bombers and attackers.

Probably yes. Did the Germans have some similar thinking as the British, in that they were planning to jump straight from their LMG to autocannons? Seems their Mg 131 only came later as a way to boost the punch of the cowling guns already after the LW had adopted autocannons?

So what if the Mg 131 would have been available earlier? Would we have seen Bf 109E's armed with 4 Mg 131 (two in the cowling plus two in the wings) instead of the historical 2 LMG's + 2 MG-FF's in the wings? And would the 131 have become their 'standard' defensive gun for bombers, similar to the M2 used by the Americans bombers?

One can quibble that the round used by the Mg 131 was too weak compared to other HMG class rounds, but I'm not so sure. It compensated by being a lightweight gun, high rpm and as a result of the modest muzzle velocity, good barrel life. Perhaps the 12.7x81SR round used by the Italian Breda-SAFAT HMG would have been a better choice, with a bit more MV, without going all the way to a really high power cartridge like the .50 BMG?

 

[tomo pauk]

es, that was what I was hinting at with my previous comment. Reasons varied, but the bottom line being that nobody really entered WWII with a good autocannon, even though many had recognized the advantages of it.

Perhaps the best was the Shvak. It didn't tick the 'has a very powerful shell' box, but that was probably the only shortcoming it had.

Probably yes. Did the Germans have some similar thinking as the British, in that they were planning to jump straight from their LMG to autocannons? Seems their Mg 131 only came later as a way to boost the punch of the cowling guns already after the LW had adopted autocannons?

Germans were even the earlier converts to the cannon armament.

So what if the Mg 131 would have been available earlier? Would we have seen Bf 109E's armed with 4 Mg 131 (two in the cowling plus two in the wings) instead of the historical 2 LMG's + 2 MG-FF's in the wings? And would the 131 have become their 'standard' defensive gun for bombers, similar to the M2 used by the Americans bombers?

A far better weapons' layout than what the Emils carried. Would've also been a better weapon than what the bombers carried.

One can quibble that the round used by the Mg 131 was too weak compared to other HMG class rounds, but I'm not so sure. It compensated by being a lightweight gun, high rpm and as a result of the modest muzzle velocity, good barrel life. Perhaps the 12.7x81SR round used by the Italian Breda-SAFAT HMG would have been a better choice, with a bit more MV, without going all the way to a really high power cartridge like the .50 BMG?

I've suggested the Germans adopting the Breda 12.7mm in many what-if scenarios, and will obviously agree with your suggestion above.

 

[marathag]

or, sorta 3/4 of a Ho-5

Or how about full sized Ho-5, with being necked down to 15mm, for being 15x94?

It does make for a heavy 85lbs gun, 104 with charging and feed accessories, but reliable gun with an overall 64" length, if keeping with the 750-850rpm.
For the cartridge case, likely to be higher MV close to the 15mm MG 151 of around 900
That's better than the .55 Boys ATR in performance, at 20 lbs more weight than a regular M3 50 aircraft mount.

 

[tomo pauk]

Or how about full sized Ho-5, with being necked down to 15mm, for being 15x94?

It does make for a heavy 85lbs gun, 104 with charging and feed accessories, but reliable gun with an overall 64" length, if keeping with the 750-850rpm.
For the cartridge case, likely to be higher MV close to the 15mm MG 151 of around 900
That's better than the .55 Boys ATR in performance, at 20 lbs more weight than a regular M3 50 aircraft mount.

Limits of the platform still apply - ie. can you fit it easy within the wings of the Bf 109E, as well as a defence gun positions on the bombers?

 

[marathag]

Limits of the platform still apply - ie. can you fit it easy within the wings of the Bf 109E, as well as a defence gun positions on the bombers?

Well, the Japanese used the 72 pound Ho-1 20mm with a 15 round magazine as a flexible gun in bombers

Since the Ho-5 was belt fed, less trouble in getting drum clearance.

It's slightly shorter overall length to the MG151/20 is also a bonus. If those could fit in the Italian FIAT G55,

could in the -109, provided the Germans were willing to use blast tubes, where they were not in OTL moving from the FF, going to the 151/20 underwing, from the ammo setup

rejigger the wing, have the Ho-5 close to where the FF was, and have a tray for the belt.

 

[Shortround6]

The ammo it uses is of the too low power, much better to use the Belgian/French 13mm round as a starting point. Even the US or Soviet 12.7mm is better bet. 13mm TuF, too.

or, Browning HMG, with barrel for 15mm ammo

Same things, for better or worse.
Same rim area and back of cartridge, with adjustments to the neck to suit the 13 (13.2)mm bullets. But that means just about the same overall length of cartridge and length of bolt travel.
Probably slightly longer if you want a 15mm projectile unless you use a short stubby 15mm shell.
Now in 1938-40 there may be a propellent problem. French, Belgians and Japanese got around 790-800ms using slightly heavier bullets than the US .50 used, but actually a big faster than the older .50 cal ammo.
It does mean that you are stuck with the weight of the .50 cal Browning and please be sure to include all the bits and pieces which the 29kg weight of the .50 sometimes listed does not do.
The German 15 X 96mm round used 57% propellent than the US .50 cal did. You can neck the .50 cal up to 15mm fairly easily. US tried at least a 16mm version if not others.
The question is what kind of velocity can you get out of it. General rule of thumb is you need about 20-21% more powder to get 10% increase in velocity (the increase it kinetic energy has to come from somewhere)

It seems to have taken around 6 years for most countries to get a gun from start up to service use. The MG 131 was mentioned in some 1939 specifications. It was used in 1941 in some bombers, it did not get into fighters until 1942. Not sure if there was an ammo problem. There may have been both mechanical priming (firing pin) and electric priming.
British Hispano was actually pretty speedy development. See demonstration, negotiate contract/license, buy land, build factory, equip and staff factory, start making guns. Expand manufacture to other locations. Simple right

Mounting some of these guns was a little complicated too.
US .50 cal M2 used more propellent per round than the 20mm MGFF/M did. and fired about 50% faster. Granted it used lighter projectiles but you can't use the same mounts/brackets you use for 7.7-7.9mm machine guns.

 

[tomo pauk]

If those could fit in the Italian FIAT G55,
could in the -109, provided the Germans were willing to use blast tubes, where they were not in OTL moving from the FF, going to the 151/20 underwing, from the ammo setup
rejigger the wing, have the Ho-5 close to where the FF was, and have a tray for the belt.

G.55 was with the bigger and thicker wing, so there is no wonder that MG 151 was a reasonably easy fit.
Spanish have introduced the additional spar on the 1-seater Buchon so the wing is strong enough even when the big holes are made through the both of the main spars, necessitated by the big HS 404 cannon to be installed. Obviously, this was not a quick and easy job as the MG FF installation.
Belt fed MG FF (or FFM) might've been easier to pull for the Germans, and to install it on existing aircraft on short notice?

Same things, for better or worse.
Same rim area and back of cartridge, with adjustments to the neck to suit the 13 (13.2)mm bullets. But that means just about the same overall length of cartridge and length of bolt travel.
Probably slightly longer if you want a 15mm projectile unless you use a short stubby 15mm shell.
Now in 1938-40 there may be a propellent problem. French, Belgians and Japanese got around 790-800ms using slightly heavier bullets than the US .50 used, but actually a big faster than the older .50 cal ammo.
It does mean that you are stuck with the weight of the .50 cal Browning and please be sure to include all the bits and pieces which the 29kg weight of the .50 sometimes listed does not do.

Weight of two .50 cal Brownings + 2 LMGs, or even of 4 of the BMGs should still be manageable for the Emil.

The German 15 X 96mm round used 57% propellent than the US .50 cal did. You can neck the .50 cal up to 15mm fairly easily. US tried at least a 16mm version if not others.
The question is what kind of velocity can you get out of it. General rule of thumb is you need about 20-21% more powder to get 10% increase in velocity (the increase it kinetic energy has to come from somewhere)

750 m/s should be enough for the 1st war years. Keeps the weight and size of both guns and ammo within modest limits.

It seems to have taken around 6 years for most countries to get a gun from start up to service use. The MG 131 was mentioned in some 1939 specifications. It was used in 1941 in some bombers, it did not get into fighters until 1942. Not sure if there was an ammo problem. There may have been both mechanical priming (firing pin) and electric priming.

This is why I like the suggestion that Germans buy the licence abroad for the HMG, and ASAP.
Alternatively, neck-down the MG FF and adopt the belt feed.

Mounting some of these guns was a little complicated too.
US .50 cal M2 used more propellent per round than the 20mm MGFF/M did. and fired about 50% faster. Granted it used lighter projectiles but you can't use the same mounts/brackets you use for 7.7-7.9mm machine guns.

Agreed.

 

[marathag]

G.55 was with the bigger and thicker wing, so there is no wonder that MG 151 was a reasonably easy fit.

Seems it didn't need all that thickness for the receiver and belt tray, a little bump on the top wouldn't be the end of the world, and would be smaller than with what the Spitfire ended up with

 

[tomo pauk]

Seems it didn't need all that thickness for the receiver and belt tray, a little bump on the top wouldn't be the end of the world, and would be smaller than with what the Spitfire ended up with

Germans themselves were not shy to add bumps when the weapon installation required so, already staring with the 109E-3*. Bumps don't solve the structural issiues, however, that was the reason why the Spanish added another spar so the wing does not break due to the weakened main spar. See here, for example.
G.55 still has an intact rear main spar, thanks to the wing being of big enough size to mount MG 151s and their ammo.

*photo of the model; bumps under the wing were due to the drum size.

 

[marathag]

Bumps don't solve the structural issiues, however, that was the reason why the Spanish added another spar so the wing does not break due to the weakened main spar. See here, for example.

Seems like the Germans didn't do enough with the Wing in going from the E to the F and G models.

 

[z42]

750 m/s should be enough for the 1st war years. Keeps the weight and size of both guns and ammo within modest limits.

I agree, and further I think one can argue it would be close to the sweet spot also later in the war, as cannons relied more on the effects of the shell exploding rather than kinetic energy.

 

[Shortround6]

There are two advantages to high velocity.
1. More kinetic energy/more destructive power
2. Easier to hit with, especially deflection shooting.

And several disadvantages.
1. As stated earlier 10% increase in velocity needs about 20% more propellent which means
A. more cost in raw materials per round of ammo. Both powder and brass (or steel) to hold it.
B. more weight of ammo per round
C. often a larger and heavier gun, and a lower cycle rate.
D. faster barrel wear.

When looking at small explosive bullets when does 1-3 grams of HE beat several thousand joules of kinetic energy of impact force?
What is cost of the small explosive bullet vs the cost of a non-explosive bullet in materials, machine time, labor? Times several million or tens of million.

I agree, and further I think one can argue it would be close to the sweet spot also later in the war, as cannons relied more on the effects of the shell exploding rather than kinetic energy.

And we are back to the conflicting basic requirements. With faster aircraft as targets (and faster shooting platforms) you have less time to aim and less time that the target is within the firing area/impact zone. Do you worry about getting hits or the effect of the hits first?
Or with 2000hp engines (and jets are way above 2000hp) do you just stick in number of large, high velocity, fast firing 20mm guns (four 20mm guns at 750rpm each) and go back to research? Nations were still arguing during the 1950s.