Alternative airborne guns

[GrauGeist]

The MK 101 & 103 guns were almost 3 times the weight of the Hispano guns. So the question is if the 103 gun was worth 3 times what the Hispano gun was. The 103 was certainly more powerful and longer ranged. but 7 shells a second compared to about 30 rounds per second from 3 Hispanos means possible destructive potential was very close. Extra range is hard to figure since Air to Air range depends on gunsights and aircraft steadiness and other factors. Percentage of times the extra range was useful?
For air to ground or ground to air the 103 has more it it's favor.

Germans were obsessed with high velocity for armor penetration. Problem is that armor penetration is not the primary goal. Destroying what the armor is protecting is the goal.
Making very small holes in armor is not destroying things behind the armor.
The MG131 was a pretty good gun considering it's weight and size. Germans didn't use multiple installations (aside from twin cowl guns) until very late in the war. A missed opportunity?

While the 30mm was a formidable weapon, the MG151/20 seemed to be a better option.
I admit the minengeschoß rounds were devastating, but saturating your target with 20mm rounds could be just as damaging.

 

[tomo pauk]

The MK 101 & 103 guns were almost 3 times the weight of the Hispano guns. So the question is if the 103 gun was worth 3 times what the Hispano gun was. The 103 was certainly more powerful and longer ranged. but 7 shells a second compared to about 30 rounds per second from 3 Hispanos means possible destructive potential was very close. Extra range is hard to figure since Air to Air range depends on gunsights and aircraft steadiness and other factors. Percentage of times the extra range was useful?

If the 101 or 103 were suitable for the engine installation, that would've meant the one 30 mm gun + two 20 mm guns on a V12 powered fighter, for a total firepower comparable to the 5 Hispanos? Or, two 30mm guns on a Fw 190?
But I don't think these big guns were an ideal fit for the historical German fighters, sorta too much of a good thing. Something that weights about 100 kg, fires the 330g M-shell at 700 m/s and at RoF of ~500 rd/min would've been a much easier thing to install and actually use. Multiple guns on 2-engined fighter. Ballistics broadly similar to the MG 151/20, and very similar to the MG FFM, so the 2+2 mixed battery makes sense.

Germans were obsessed with high velocity for armor penetration. Problem is that armor penetration is not the primary goal. Destroying what the armor is protecting is the goal.
Making very small holes in armor is not destroying things behind the armor.

Defeating the armor will much increase the chance of killing or incapacitating the pilot.

The MG131 was a pretty good gun considering it's weight and size. Germans didn't use multiple installations (aside from twin cowl guns) until very late in the war. A missed opportunity?

I'd cancel the MG 131 already on the paper stage, and focus on 20-30mm stuff instead. Eg, the belt-fed MG FF or FFM would've been a far better asset already in 1940, ditto for an useful air-to-air gun in 23-25-30mm range.

 

[Shortround6]

Something along the lines of a P-47, F4U/F6F or Hawker Typhoon/Tempest would be needed for a plane carrying a MK 103 in each wing.
MK 103 had problems with being synchronized. Problem was not so much timing the primer initiation (firing pin or electrical impulse) but that large capacity cartridge cases do not have uniform burn times and the lock time (electric impulse to shell exiting the muzzle) varied more than small shells. Hitting your own prop with a 13mm or 20mm shell was bad enough, hitting the prop with 440g shell at 800ms was really going to ruin the pilot's day.
A smaller, lower powered gun that fired faster would have been a much better choice as you have been saying.

Defeating the armor will much increase the chance of killing or incapacitating the pilot.

Perhaps, but such rounds might very well be less effective if they hit anywhere else or at least less effective in many locations even if effective in some.

I'd cancel the MG 131 already on the paper stage, and focus on 20-30mm stuff instead. Eg, the belt-fed MG FF or FFM would've been a far better asset already in 1940, ditto for an useful air-to-air gun in 23-25-30mm range.

A lot depends on weight and volume that can be devoted to the gun/s. MG131 was supposed to be interchangeable with the MG15/17. It sort of failed at that but it came close.
It was the most weight efficient gun of the 12.7/13mm guns.
Since you can't synchronize an Oerlikon gun, even with a belt fed, that leaves the Germans short of cowl guns. Oerlikon guns don't really work well as flexible guns for bomber defense (Germans tried) and they don't work in turrets unless you can get the belt feed to work. Germans never tried that. Belt feed was fixed mount only.
MGFF/Type 99-1 fired much heavier shells than the MG 131 but at about 8 shells per second vs 15rps and with their heavier weight the 20mm advantage, while there, is not so clear cut.
Germans made a complete botch of manned power turrets trying to mount larger guns. Tried to run before they could totter let alone walk.

Germans could have/should have decided on a lot fewer projects of less than "super" performance and gotten a decent weapon into service.
In 1942 the Germans wanted a "million point gun" 1000rpm at 1000m/s but that time they had just gotten a 1/2 million point gun into service (MG 151/20 without mineshells).
They should have picked one or the other. The 1000rpm at 700m/s or 700rpm at 1000/s or perhaps 800rpm at 800m/s.
British ended the war with a 600,000 point gun. MK V Hispano with 720rpm and 830m/s with 130 gram shells.
Germans settled for the MK108. Great destructive power, lousy ballistics for air-air combat. Perhaps try for a 50% increase in effective range rather than trying to double it?

I would note that the US had lots and lots of experimental cartridges and guns during WW II. Most went nowhere.

 

[tomo pauk]

Perhaps, but such rounds might very well be less effective if they hit anywhere else or at least less effective in many locations even if effective in some.

It will be definitely less effective hitting the other locations - the 'no free lunch rule' applies everywhere.

Since you can't synchronize an Oerlikon gun, even with a belt fed, that leaves the Germans short of cowl guns.

Excellent - the earlier the cowl MGs are dispensed with, the better is for the German fighters.

Oerlikon guns don't really work well as flexible guns for bomber defense (Germans tried) and they don't work in turrets unless you can get the belt feed to work.

I'm not sure that I've ever read that the Oerlikon-type guns don't work as flexible guns, be that in German or IJN aircraft.
Yes, make them belt-fed ASAP - both fighters and bombers need them.

MGFF/Type 99-1 fired much heavier shells than the MG 131 but at about 8 shells per second vs 15rps and with their heavier weight the 20mm advantage, while there, is not so clear cut.

Two hits by M-shells, or even the 'classic' 115-140G shells should suffice to bring down a fighter that is not a Beaufighter or a P-47.

Germans could have/should have decided on a lot fewer projects of less than "super" performance and gotten a decent weapon into service.

For my money, after the good/very good MG FF, FFM and MG 151 cannons, their next air-combat cannons were each with gaping holes (one with very low MV, other two with serious problems wrt. the installation on the mass-produced fighters of the day). A more ballanced weapon or two would've served them much better in air combat.

In 1942 the Germans wanted a "million point gun" 1000rpm at 1000m/s but that time they had just gotten a 1/2 million point gun into service (MG 151/20 without mineshells).
They should have picked one or the other. The 1000rpm at 700m/s or 700rpm at 1000/s or perhaps 800rpm at 800m/s.
British ended the war with a 600,000 point gun. MK V Hispano with 720rpm and 830m/s with 130 gram shells.

The 1000*1000 request means it must be a 20mm gun or smaller - anything bigger for a 'million' will be too heavy and too big, even worse than the MK 101/103. For fighting the heavies, a much heavier shell is needed than the 90-110g shell from a 20 mm gun*
So indeed, they needed something more down to earth, but in a heavier calibre, that is still a good fit for the fighter of a day.

(*for comparison sake, Germans looked at a twin 37mm as a minimum for land-based air defences come 1944; preferably a triple 37mm or a twin 50-55mm !!!).

Germans settled for the MK108. Great destructive power, lousy ballistics for air-air combat. Perhaps try for a 50% increase in effective range rather than trying to double it?

Agreed all the way.
As a back-up for the places the 'MK 105' will not fit (like the wings of the fighters), a MK 108 with a ~250g shell and close to 700 m/s might've been interesting.

 

[z42]

A lot of HE rounds had trouble penetrating inside the aircraft and exploded on the skin. This could be solved with time (better fuses) and cost.
What works on a fighter often does not work on a bomber.

I seem to recall that Germany explicitly designed the fuses on their mine shells to explode just after penetrating the skin. The logic may have been that 1) If you hit the wing, particularly when deflection shooting, you want the shell to explode inside the wing and not pass out the other side before exploding 2) For aircraft of stressed skin construction (semi-monocoque) blowing out skin panels can have a serious effect on structural integrity. As well as aerodynamic efficiency?

 

[z42]

If the 101 or 103 were suitable for the engine installation, that would've meant the one 30 mm gun + two 20 mm guns on a V12 powered fighter, for a total firepower comparable to the 5 Hispanos? Or, two 30mm guns on a Fw 190?
But I don't think these big guns were an ideal fit for the historical German fighters, sorta too much of a good thing. Something that weights about 100 kg, fires the 330g M-shell at 700 m/s and at RoF of ~500 rd/min would've been a much easier thing to install and actually use. Multiple guns on 2-engined fighter. Ballistics broadly similar to the MG 151/20, and very similar to the MG FFM, so the 2+2 mixed battery makes sense.

IMHO the "sweet spot" for a German WWII aircraft cannon would have been something around 200-250g M-shell at 700-750 m/s. Also, even at the cost of worse external ballistics, maybe a short and stubby shell and a straight-walled cartridge would have enabled a shorter cycle and thus faster RoF, and more compact packing of ammo belts. At the usually short ranges WWII air combat happened at, the worse ballistics of a short and stubby shell might not matter that much.

 

[SaparotRob]

Phasers.

 

[MIflyer]

The later version of the B-25's 75MM gun was used on the Chafee light tank.

And the 75MM gun was removed on some CBI B-25H and replaced with rocket tubes.

 

[Shortround6]

Excellent - the earlier the cowl MGs are dispensed with, the better is for the German fighters.

This sort of depends on timing. By late 1943/early 1944 the Cowl MG 131s were not paying their own way (fire power for weight) against allied bombers and most western fighters.
If they had gotten them into production in large numbers in 1941 the increase in firepower, especially for the Bf 109F, would have been a lot more significant.

I'm not sure that I've ever read that the Oerlikon-type guns don't work as flexible guns, be that in German or IJN aircraft.

The gun/s worked, as guns. They did shoot down some attackers. But using 15-30-60 magazines/drums means a lot of time reloading and not shooting. Most of the Japanese and early German turrets/mounts were not powered and trying to aim even small 20mm guns was not easy. Were they really that effective vs the weight of the gun/installation?

Yes the Type 99 with a 60 round drum

was much more effective than one or two Lewis guns but by 1940-41 one would hope they had some thing more effective than a 1915-16 Lewis gun.
yes I used one of the worst (highest drag) 20mm installations

Two hits by M-shells, or even the 'classic' 115-140G shells should suffice to bring down a fighter that is not a Beaufighter or a P-47.

Well, bringing down and ending the fight are not quite the same thing. A number of smaller Allied fighters made it home after getting hit by two or more 20mm shells, but they were usually trying to get away rather than shooting back. German 115-117G shells held about 1/2 ( 3.7G?) the HE of a Hispano Shell. For some reason the Germans didn't make many (any?) 115-117G HE shells. They were mostly HE/tracer and the tracer compartment took up a fair amount of space.

For my money, after the good/very good MG FF, FFM and MG 151 cannons, their next air-combat cannons were each with gaping holes (one with very low MV, other two with serious problems wrt. the installation on the mass-produced fighters of the day). A more ballanced weapon or two would've served them much better in air combat.

I agree 100%

 

[Shortround6]

IMHO the "sweet spot" for a German WWII aircraft cannon would have been something around 200-250g M-shell at 700-750 m/s. Also, even at the cost of worse external ballistics, maybe a short and stubby shell and a straight-walled cartridge would have enabled a shorter cycle and thus faster RoF, and more compact packing of ammo belts. At the usually short ranges WWII air combat happened at, the worse ballistics of a short and stubby shell might not matter that much.

200 to 250 G may not sound like big change but is about a 25% change in energy which requires a roughly 25% change in propellent charge, assuming other things stay the same.

I have gathered up some 20mm shells and few more to show propellent charges.
gun..,,,,,,,,,,,.............propellent charge/G....................... shell weight/G.........................MV/MS.................length of round/mm
Oer F/typr 99-1...............13.5....................................................128........................................605................................140-145
MG/FF.................................13.5....................................................134........................................600.................................145
MG/FFM.............................15.5.....................................................92..........................................700.................................145
MG 151...............................19........................................................92...........................................800................................147
MG 151...............................19......................................................115...........................................710................................147
Ho-5.....................................20.......................................................79.........................................730-750..........................145?
ShVAK..................................18....................................................91-96......................................750-810..........................145
Type 99-2...........................21.4...................................................128...........................................750................................173
Oer FFS...............................28.5....................................................128...........................................830................................181
Hispano..............................32.5....................................................128.......................................850-880...........................184
Ho-1/3.................................37........................................................136.........................................820..................................195
20 x 138............................36.5-44...........................................101-147.................................800-975............................203
23x106 Madsen..............34.5......................................................174........................................720...................................186
23x115 Russian............33-37..................................................175-200...............................690-710.............................200(?)
25mm Hotchkiss AA...160........................................................250........................................900.....................................233
MK 108..............................30..........................................................330.......................................505...................................----
Aden LV............................---..........................................................273........................................604..................................----

Propellent charges for the newer cannon seem to be harder to get.
One French loading for the 30 x 113 Aden (?) gun uses 50 grams to get a 275g shell up to 775ms a second.
Overall length is about the same but this is thick walled projectile and they traded shell length for propellent space and used more modern propellent.
Late war Japanese 30mm guns may have had problems with steel quality as they don't seem to use very high pressures.

 

[MIflyer]

Well, bringing down and ending the fight are not quite the same thing.

 

[tomo pauk]

This sort of depends on timing. By late 1943/early 1944 the Cowl MG 131s were not paying their own way (fire power for weight) against allied bombers and most western fighters.
If they had gotten them into production in large numbers in 1941 the increase in firepower, especially for the Bf 109F, would have been a lot more significant.

Timing is a key property of a weapon
Keeping the wing MG FFMs on the 109Fs from 109E4s/E7s doubles the firepower vs. what they carried in 1941-42, a bar the two MG 131s cannot hope to match, not even the two Berezin's HMGs. Delete the cowl guns.
Money, time and resources used to sped-up the MG FFM, as well as to provide it with belt feed mechanism (by 1940, or by 1941 at latest) would've been much better spent than spending them on the development of the MG 131.

If Germans really must have a HMG - they need to start out earlier, and with a more powerful cartridge. Even piggy-back on the Belgian Brownings would've been a faster way to acquire a world-class gun in a timely manner.

The gun/s worked, as guns. They did shoot down some attackers. But using 15-30-60 magazines/drums means a lot of time reloading and not shooting. Most of the Japanese and early German turrets/mounts were not powered and trying to aim even small 20mm guns was not easy. Were they really that effective vs the weight of the gun/installation?

I've suggested, many times, the belt feed to be developed for the Oerlikons by late 1930s/early 1940s (instead of waiting until late 1942/1943 for the Japanese and Germans in the historical timeline). Weight of the MG FF and it's derivatives will not be that bigger than what the powerful HMG weights.

Well, bringing down and ending the fight are not quite the same thing. A number of smaller Allied fighters made it home after getting hit by two or more 20mm shells, but they were usually trying to get away rather than shooting back. German 115-117G shells held about 1/2 ( 3.7G?) the HE of a Hispano Shell. For some reason the Germans didn't make many (any?) 115-117G HE shells. They were mostly HE/tracer and the tracer compartment took up a fair amount of space.

The Mine shell was far more destructive, have had the higher MV and was probably much cheaper to make than the 'normal' ~115G shell.

200 to 250 G may not sound like big change but is about a 25% change in energy which requires a roughly 25% change in propellent charge, assuming other things stay the same.

A bigger & heavier 20mm cannon (like Hispano or the Ho-1/-3) should be a better base for the 23-25mm development than the lighter 20mm cannon.
The VJa-23 already offers 200g shell at very high MV and useful RoF; as a 25mm necked-up version should've been also very interesting, and a much more relistic air-fighting gun that the powerful 37mm the Soviets made in ww2). A gun worthy of copying by the Germans, IMO.
Another way towards the (German) 25mm would've been the development of the MK 108 - trading the shell weight for a hefty increse of MV. But already a 30mm ~250g shell would've much improved the short-range ballistics of the 108.

 

[Shortround6]

If Germans really must have a HMG - they need to start out earlier, and with a more powerful cartridge. Even piggy-back on the Belgian Brownings would've been a faster way to acquire a world-class gun in a timely manner.

Germans started with the MG 131 in 1938. Guns (all nations) seem to have taken longer to develop/get into production than anticipated.
1 1/2 to two years earlier than trying to piggy-back the FN Browning?
Whole idea behind the MG 131 was to be able to replace MG 15s and MG 17s on a pretty much one for one basis. An extra 5kg per gun?
Using the FN Browning meant a gun 12kg heavier than the MG 131, well into the small 20mm gun range instead of being 7-11kg less in weight than the small 20mm guns.
Here is where timing comes into play again. The MG 131 fired bullets about 3 times heavier than the German 7.9mm gun and fired about 75% as fast, result was just over twice the power. Belgian FN was supposed to fire even faster, unknown is the rate of jams or the barrel life. Actual power of the FN was just a bit under the American .50. heavier bullets going slower. Americans boosted their MV by over 90ms in 1940/41.
The MG 131 was a more powerful gun than the Italian 12.7mm guns and pretty much equal to the Japanese Ho-103 while being about 75% as heavy as the Japanese gun.
Soviet 12.7mm was in class of it's own.

I've suggested, many times, the belt feed to be developed for the Oerlikons by late 1930s/early 1940s (instead of waiting until late 1942/1943 for the Japanese and Germans in the historical timeline). Weight of the MG FF and it's derivatives will not be that bigger than what the powerful HMG weights.

So basically develop a belt feed, increase the rate of fire and lighten up the 20mm gun all at the same time?
A lot is made of the light weight of the MG FF gun (and Japanese type 99) while overlooking the poor rate of fire and the often overlooked roughly 10kg weight of the 60 round drum.
Hispano is also often not counting the weight of the drum. Converting to belt feed does not get rid of all the drum weight. Most of it is converted to a belt feed system. Perhaps a bit lighter. 6-8kg? but that means the MG FF is now a 35kg gun?
The Oerlikon is still more powerful, but the weight advantage has gotten smaller.
The MG 151/20s weight of 42kg actually includes the belt feed. A stripped MG 151 is closer to 37kg.
The Oerlikons throw a shell just as powerful as the Hispano even without the mineshell. But they fire slow, and the shells are slow in the MG FF. Firing 8 shells per second instead of 15 of the MG 131 or 13 for the US .50 means fewer hits. The lower velocity means they are harder to hit with. The MG 131 is the least powerful HMG but it's time of flight is no worse than the MG Ff and in some cases, a bit better.
Tasking a blowback gun with powering a belt feed system is certainly not impossible, but it may affect cycle rate a bit and may not like operating at high G loadings.

By the time you get a belt feed on the MG Ff gun and give it enough shells to make it worthwhile the weight difference may be close to a 2 to 1 ratio. The 20mm MG FF is still a more powerful weapon for its weight but it is not the runaway it looks at first glance.

 

[z42]

200 to 250 G may not sound like big change but is about a 25% change in energy which requires a roughly 25% change in propellent charge, assuming other things stay the same.

My intention was to paint in broad strokes, not pin down some specific values to five decimal places. Indeed my range 200-250g at 700-750m/s covers a KE range between 49 and 70kJ. My broad idea would be to have more punch than the Mg 151/20, but higher MV than the Mk 108 while still keeping the weight of the gun within reasonable bounds (unlike Mk 103, say). Thus compromise a bit on the 330g shell weight of the Mk 103&108.

 

[MIflyer]

Keeping the wing MG FFMs on the 109Fs from 109E4s/E7s doubles the firepower vs. what they carried in 1941-42,

I've read that firing the wing guns on the BF-109E led to vibration of the ailerons, resulting in the RAF calling the airplane the "Flutterschmidt."

 

[Shortround6]

My intention was to paint in broad strokes, not pin down some specific values to five decimal places. Indeed my range 200-250g at 700-750m/s covers a KE range between 49 and 70kJ. My broad idea would be to have more punch than the Mg 151/20, but higher MV than the Mk 108 while still keeping the weight of the gun within reasonable bounds (unlike Mk 103, say). Thus compromise a bit on the 330g shell weight of the Mk 103&108.

There were about 3 different ways of causing 'damage' with air to air guns.
1. Kinetic energy. Basically solid shot at high velocity just crashing its way through the target aircraft. Assumes that there is something vital in the path of the bullet/projectile.
2. German Mine shells. A lot of HE, using pressure/blast to damage things out to the sides of impact point/path. Not much in the way of heavy fragments.
3. Normal HE shells. A lot less HE but more steel for more/heavier fragments that travel further from the explosion point.
Keeping out incendiary at the moment.
During WW II only the Germans used mine shells. British and French used them in the late 40s/early 50s (and later).
The mine shell gave several advantages to the Germans in that it not only doubled the weight of HE in a 20mm shell, the lighter weight increased velocity from about 600m/s to 700m/s for shorter time of flight. But it meant the Mine shell didn't have much penetration and while the blast was impressive it didn't work as well in large spaces. Depending on type of aircraft and location of hits it could be better than a conventional shell or worse.

A gun with a KE of 70kJ is going to be bigger and heavier than a gun with 50KJ. How much heavier is the question. This assumes the same/similar rate of fire.
The MG 151/20 was quite similar in "power" to the larger, heavier Hispano gun. In part because of it's higher cycle rated. Firing about 20% more shells per second helps. The Mine shells helped but mine shells were only around 40-60% of the ammo load. Hispano shells were rather destructive even if the fuse failed. Assuming there was anything large in the plane for the Hispano to hit and not just pass through a couple of layers of skin the Hispano had the potential to do about up to 50% more damage than a MG 151/20 shell (dud).

A lighter 30mm shell would help velocity but at the cost of less HE. External ballistics is something of problem. The lighter shell will slow down faster than the heavy shell. Yes it starts out faster, at what point do the shells pass each other or more importantly, when does the light shell have a longer time of flight than the heavier shell? Given the sighting systems of time should they even be trying to fire at such ranges?

What else did the MK 108 have going for it?
What would you willing to lose in order to get the benefit/s you want?
Using WW II technology and not 1949-1953 technology.
British 30mm Aden M3 used a 273g shell at 600-605ms for 49,800KJ compared to the German MK 108 42,100KJ. Also used a 108cm barrel instead of 44cm barrel.
Japanese had 4 (?) different 30mm cartridges and guns. Two fired at 400rpm and two fired at 500rpm instead of the German 600rpm.
Most (all) were lighter than the MK 108 but if they only fire 2/3rds as fast and fire shells that weigh 235-273g what are you paying for the higher velocity?
maybe it is worth it, maybe not.
The MK 108 was flawed, fixing it's flaws was going to cost something, weight or rate of fire or destructive effect per shell.

 

[tomo pauk]

Germans started with the MG 131 in 1938. Guns (all nations) seem to have taken longer to develop/get into production than anticipated.
1 1/2 to two years earlier than trying to piggy-back the FN Browning?
Whole idea behind the MG 131 was to be able to replace MG 15s and MG 17s on a pretty much one for one basis. An extra 5kg per gun?

Replacing the LMGs with a weak-ish HMG on the fighters, for a country that is already introducing 20mm cannons of interwar 1st gen and moving to the 15mm cannon and the 2nd gen 20mm is a money badly spent.
The Belgian Brownings were functional weapons in mid 1940 when the Germans occupied Belgium, while the Germn 13mm was a functioning & actually available weapon in 1943? Even if Germans draw their feet, they can save themselves at least a year with Belgian guns and have their engineers that are working on the MG 131 design something more substantial from 1940. Forget the cowl guns by the time 109F is in play, and use the HMGs as the defensive weapons.

So basically develop a belt feed, increase the rate of fire and lighten up the 20mm gun all at the same time?

Hopefully you can quote me saying that MG FF(M) needs to be lightened, and that all improvements need to happen in the same time.

Swiss sped up their guns at least once in the 1930s, while IJN further sped up their Oerlikons twice between 1943 and 1945. Germans experimented with increasing of RoF of the MK 108 from 600 to 850 (going to 1200 rd/min was judged as needing the fancy materials they were short come 1944/45). Swiss, Japanese and Germans each made separate belt-feed mechanisms for the Oerlikons (perhaps the japanese have had some support by the Swiss?). Speeding up the API guns was easily achieved by the lighter recoiling mass, stronger springs and introduction of buffers (mostly in the form of spring buffer).
Adding belt feed before 1940, or at least before 1941 should've been doable by a competent companies of the time, and increase in the RoF can happen by 1941-42.

Tasking a blowback gun with powering a belt feed system is certainly not impossible, but it may affect cycle rate a bit and may not like operating at high G loadings.

Seems like the Japanese Oerlikons worked just fine.
Germans used the electric motors to feed the belt into the MG FFM on the Do-217 night fighters.

I've read that firing the wing guns on the BF-109E led to vibration of the ailerons, resulting in the RAF calling the airplane the "Flutterschmidt."

Too many Allied crewmen died to the Emil's cannons to take this into a serious consideration.

 

[muskeg13]

Smothered with 30mm hits, hit multiple times with an aerial 105mm howitzer (larger than anything employed in WW2, the Piaggio P.108 with a 102mm/4 inch) , and the USS Mobile Bay (CG‑53) had to be sunk with a real ship killing weapon, a torpedo. Aerial cannon are not effective in destroying large ships.


View: https://www.youtube.com/watch?v=-25qudVrUnU&t=315s

 

[MIflyer]

Too many Allied crewmen died to the Emil's cannons to take this into a serious consideration.

Except for the ones who did not die because the gunnery was not accurate.

 

[Shortround6]

The Belgian Brownings were functional weapons in mid 1940 when the Germans occupied Belgium, while the Germn 13mm was a functioning & actually available weapon in 1943?

MG 131 started, on paper, in 1933, It didn't get much further until 1938. It was a functioning weapon in 1940 and was being fitted to the Me 210 and the Do 217. Why is took until 1942/43 to get into single seat fighters I don't know.
FN had the sales rights for the Browning machine guns in Europe. How many were made there is subject to question. FNs work on developing the big Browning is also a bit of a mystery. Many of the large Brownings sold by FN were actually manufactured by Colt in the US and stamped/restamped/proofed in Belgium before being shipped to customers.
FN was certainly doing a lot of work on the BAR that Colt was not doing. Who was doing what to the small Browning belt feed gun is a question at the moment.
FN was certainly selling 13.2mm machine guns but I don't know if Colt or FN was making the barrels for these guns and fitting them to Colt receivers. Might depend on batch of guns in question. The Germans did not capture a factory capable of making hundreds of heavy machine guns per month. They captured a factory capable of making a lot of rifles, pistols, shotguns and light machineguns (BAR) with the drawings and some small scale tooling for the belt feed guns.

Even if Germans draw their feet, they can save themselves at least a year with Belgian guns and have their engineers that are working on the MG 131 design something more substantial from 1940. Forget the cowl guns by the time 109F is in play, and use the HMGs as the defensive weapons.

I have been trying to point out that the MG 131 and the FN/Colt are very different guns. The MG 131 was the smallest, lightest HMG made in WW II. The FN/Colt was the largest and heaviest (not including the the 15mm weapons). Soviet 12.7 was more powerful but it was lighter and a bit skinnier. Chances of squeezing in a pair of FN/Colts into the cowl of a 109 is slight. Want to try putting a pair of the FN/Colts into the that FDL 131 contraption in the Me 210?
More production in 1940/41 might have helped the Germans, continued production in 1944 probably didn't (one source they stopped in 1944 ?)
Germans could not know in 1938/39 they would capture the FN factory or what condition it would be in. The MG 131 was produced in at least 4 factories, perhaps not all at the same time or in similar quantities?
MG 131 was the most weight efficient HMG except for the Soviet 12.7mm UB. Sometimes by a lot (Breda 12.7mm) and sometimes by only a little (Ho-103). The MG 131 was very similar in cartridge power to the Italian guns and the Ho-103. It fired faster than the Italian guns and it was lighter than the Italian guns and the Japanese gun.

Hopefully you can quote me saying that MG FF(M) needs to be lightened, and that all improvements need to happen in the same time.

Well, if you are saying it could have been used in place of heavy machine gun/s you either need to lighten it or accept the weight penalty.
What time frame do you want to use? Adopt the Oerlikon guns in 1939 so you can have fast firing, light guns in 1944?

What we don't know is what some countries may have given up to get the higher rates of fire or what the increased costs were.
Took the US from around 1942 to early 1945 to get the .50 cal Browning up to 1200rpm.
In part due to stupid requirements. Like being able to use a parts kit in existing guns (failed) and trying to keep the parts breakage/jams at the same level as slower firing guns.
US could have had a 1200rpm .50 cal in 1943 if they accepted a new receiver not interchangeable with the existing guns and would put up with more broken parts/malfunctions but the US forces were not happy with the slow firing .50s in 1942/43 as it was.
MG 131 was supposed to have very good barrel life (too good?) American .50 cal burned out barrels at 800rpm. Used chrome lined bores to help. Then they went to Stellite bore inserts. Same stuff they used on exhaust valves and valve seats and some parts of turbo chargers. Not sure that anybody but the US could afford to do that. Maybe other people just bult more plain steel barrels.
British accepted more malfunctions from the 720-750rpm Hispano Vs than the 600rpm HIspano IIs. They wanted the firepower. I have no idea what the Japanese were willing to put up with or maybe they got the higher rate of fire with no problems?

Germans used the electric motors to feed the belt into the MG FFM on the Do-217 night fighters.

And what did that contraption weigh?