Why no heavier RAF machine gun calibres?

[Admiral Beez]

What did the British think of the .50cal mgs on US fighters? Did the Air Ministry ever consider changing from .303 to .50 before their experience with US aircraft? There was the Vickers .50 machine gun used on ground and ship applications.


View: https://www.youtube.com/watch?v=cHTAelAI8UQ

I suppose the Brits figured if a heavier projectile was needed they'd install the 20mm cannon, while keeping .303 production could efficiently serve both the army and air force.

British .303 vs 50 Cal M2

Were Browning M2 50s ever considered as armament for British planes? The RAF seems to have settled on .303 rifle or 20 mm cannon for armament. Reading Korda's With Wings Like Eagles, Korda credits Dowding for insisting on eight .303 minimum for the Hurricane and Spitfire. A Hurricane armed...

ww2aircraft.net

 

[PAT303]

More BS has been written about this subject than anything else. The RAF from as far back as the early 1930's were looking at different guns for their fighters and many different types were trialed, a lot many people have ever heard about, there are lots of things to consider. For a start you have to get it to work, manufacture it, mount it in the plane and have the thing up and running before 1939 which means deciding on a weapon from about 1936-7 at the latest, then you have to consider how to get the thing off the ground, there's no 1500hp engines in 1939 so weight is an issue, bigger guns less fuel, more fuel littler guns or settle for lower overall performance, you have to pick. The RAF rightly chose the Browning .303, it was light, it was reliable, it had ammunition that was designed specifically for air fighting that did actually work and lastly there were eight of them when the opposition had either two, or one MG and one HMG or a mix of two of each, or in the case of the higher dash number Me109 the FF cannon that didn't work so they had to redesign it to the FF/M that did with limited drum feed that couldn't use mixed ammunition. The RAF looked at all the options and after realising the Browning .50 cal didn't work and neither did it's ammunition not to mention by the time the BoB started only about 6000 had been made, and most of them were not aircraft guns they were better of not wasting time with the .50 and just start with the bigger Hispano instead which is what they did.

 

[Thumpalumpacus]

Holy run-on sentence!

 

[z42]

We had a longish thread discussing this a little less than a year ago.

UK goes all-in on a HMG class gun in the mid-30'ies

So historically the UK decided in 1935 in specification F.37 (or something like that, too lazy to look up right now) that the next generation fighter would be equipped with 20mm cannons, in essence deciding to skip over the .50 cal and going straight from the rifle caliber .303 to an autocannon...

ww2aircraft.net

Tl;dr: They decided already in 1935 that the next generation aircraft gun after the 303 would be a 20mm cannon. So they never bothered with developing a HMG class gun for aircraft use.

 

[Admiral Beez]

They decided already in 1935 that the next generation aircraft gun after the 303 would be a 20mm cannon.

Too bad a belt-fed 20mm wasn't available for the Whirlwind. Those tiny drums were never going to cut it. Given the plans in the mid-1930s to rely on 20mm cannons, why was there no design for serpentine belts like those on the .303 and .50 mgs? Put the Whirlwinds ammo behind our pilot, snaking beneath and up to the guns, assuming CoG can be addressed. Also, the rear guns on the four engined bombers would have benefited.

 

[Shortround6]

Too bad a belt-fed 20mm wasn't available for the Whirlwind. Those tiny drums were never going to cut it. Given the plans in the mid-1930s to rely on 20mm cannons, why was there no design for serpentine belts like those on the .303 and .50 mgs? Put the Whirlwinds ammo behind our pilot, snaking beneath and up to the guns, assuming CoG can be addressed. Also, the rear guns on the four engined bombers would have benefited.

You are vastly over complicating things.
There was room for around 120rpg gun in the Whirlwind, no need for yards of bullets snaking around the pilot. Not to mention the weight.

Putting a four 20mm gun tail turret in even a 4 engine bomber requires an absolutely huge bomber.

Fighter with twin Vultures.
There were several proposals to mount both dorsal and ventral 4 gun turrets on large bombers. Putting a 4 gun tail turret in a bomber requires something bigger than than B-29.
Size and weigh of the turret goes up with the cube of the caliber of the guns. So roughly 8 to 9 times the size/weight of the four .303 gun turret?

 

[Shortround6]

What did the British think of the .50cal mgs on US fighters? Did the Air Ministry ever consider changing from .303 to .50 before their experience with US aircraft? There was the Vickers .50 machine gun used on ground and ship applications.

As explained other places. The Vickers guns didn't do well in remote mounts (like wings).
The American .50 was tested, several times, but it was not the gun of 1940 in the .30s.
The gunpowder needed more development and that happened in 1939-40 and boosted the velocity by around 100m/s. Significant increase power.
The 20mm offered higher velocity, much greater shell weight and roughly an equal rate of fire compered to the existing .5 in machine guns. And all of the existing .5in guns needed work.

 

[z42]

Too bad a belt-fed 20mm wasn't available for the Whirlwind. Those tiny drums were never going to cut it.

Presumably there was plenty of room in the nose of the aircraft for bigger drums? Although bigger drums than the 60 rounds magazines they had might not have been feasible to make reliable as long as they worked by spring tension? You're on the verge here of inventing the modern linkless feed systems (which in reality were developed in the 1950'ies to deal with the rotary cannons then coming into service).

Given the plans in the mid-1930s to rely on 20mm cannons, why was there no design for serpentine belts like those on the .303 and .50 mgs? Put the Whirlwinds ammo behind our pilot, snaking beneath and up to the guns, assuming CoG can be addressed. Also, the rear guns on the four engined bombers would have benefited.

It seems in general the development of a working cannon was quite slow after the initial choice was made; perhaps it was felt that there were higher priority items to spend money on.

As for having the ammo belts behind the pilot and sneaking past him, that probably requires some kind of feed motor or such to avoid damaging the belt links. IIRC there were some bombers where the ammo for the tail gunner was stored further forwards in the aircraft, and the belts were fed to the guns with electrical feed motors (someone might have posted a picture in that previous thread I posted a link to above?).

 

[z42]

Speaking of linkless feed systems and you're wondering what the heck that is, here's a report describing one such system, along with pictures which might give you an idea how it works. Oh, and it includes Fortran source code for computing a few details, like cam profiles!

https://apps.dtic.mil/sti/pdfs/ADB004677.pdf

 

[z42]

Putting a four 20mm gun tail turret in even a 4 engine bomber requires an absolutely huge bomber.

There were several proposals to mount both dorsal and ventral 4 gun turrets on large bombers. Putting a 4 gun tail turret in a bomber requires something bigger than than B-29.
Size and weigh of the turret goes up with the cube of the caliber of the guns. So roughly 8 to 9 times the size/weight of the four .303 gun turret?

Not sure where the suggestion for a 4x20mm turret comes from here? As for not fitting into existing aircraft, isn't that mostly an effect of CG (which IIRC is what doomed plans to install a 20mm rear turret on the Lancaster)? But if the aircraft is designed from the outset to carry the weight of the 20mm turret in the back (or wherever those turrets are to be placed), then it shouldn't be an issue, at least from a CG perspective?

As for that Vulture-powered fighter, what god-forsaken abomination is that? Some kind of next-generation Boulton Paul Defiant?

 

[Shortround6]

As for that Vulture-powered fighter, what god-forsaken abomination is that? Some kind of next-generation Boulton Paul Defiant?

yep, they even built a 1/2 scale flying "model".

 

[PAT303]

Holy run-on sentence!

Haha sorry about that, I replied after being out treating a young boy with strep throat, I don't do gooda wryting at 1am in the morning.

 

[Alan Stevens]

The RAF rightly chose the Browning .303, it was light, it was reliable, it had ammunition that was designed specifically for air fighting that did actually work and lastly there were eight of them when the opposition had either two, or one MG and one HMG or a mix of two of each

So basically the torrent of .303 slugs from 8 guns could do about the same damage as two 50 cal?

 

[J.A.W.]

So basically the torrent of .303 slugs from 8 guns could do about the same damage as two 50 cal?

Depends on the target,

I recall reading the memoir of an RAF Hurricane pilot operating during the retreat through the (then) Dutch East Indies under the onslaught
of the forces of Imperial Nippon. He had the 12 x .303" variant, & related the effect of unleashing that storm of lead on a barge packed with enemy soldiers, who of course were hacked down haplessly/ruthlessly.

 

[PAT303]

So basically the torrent of .303 slugs from 8 guns could do about the same damage as two 50 cal?

No, for a start each .303 was good for around 1150-1200 RPM where's the .50 cal was if we are being honest good for about 450 RPM so we are talking 150-160 .303's per second to 15 .50 cals, also remember they were lower velocity rounds not M2's. You also have to take into account both the .50's would most likely jam in combat and didn't have specialised ammunition, the first incendiary rounds for the .50 we upscaled de wilde .303 rounds. In 1940 the .50 cal wasn't even close to being a developed aerial weapon and in my opinion 300 de wilde AP and ball rounds from eight .303's, 2 second bursts are the quoted figure for an effective hit on the target would be far more effective than what two .30's or two .50's or four 8mm's could do.

 

[ThomasP]

For the Air Exercises in the mid- to late-1930s the RAF/Air Ministry figured 1x 20mm equaled 2x .5"/.50 cal equaled 4x .303 cal. As was mentioned upthread, however, the intent was already to adopt 20mm weapons and bypass the .5"/.50 cal weapons. Air Ministry tests in the 1930s had shown that the 20mm was clearly superior against most targets. Note, that for the most part this was before the advent of the 4-engine heavies, and before most aircraft had any significant armour or SSFT protection (most actually had none).

 

[yulzari]

You are vastly over complicating things.
There was room for around 120rpg gun in the Whirlwind, no need for yards of bullets snaking around the pilot. Not to mention the weight.

Putting a four 20mm gun tail turret in even a 4 engine bomber requires an absolutely huge bomber.

View attachment 759762
Fighter with twin Vultures.
There were several proposals to mount both dorsal and ventral 4 gun turrets on large bombers. Putting a 4 gun tail turret in a bomber requires something bigger than than B-29.
Size and weigh of the turret goes up with the cube of the caliber of the guns. So roughly 8 to 9 times the size/weight of the four .303 gun turret?

A trials Wellington carried a 40mm in a powered turret.
Martin Baker I believe made both a 4x20mm belted installation for the Whirlwind and a 12x.303" alternative. The latter did not so much pierce armour as remove the airframe from around it.

 

[Thumpalumpacus]

We had a longish thread discussing this a little less than a year ago.

Please tell me that one had punctuation!

 

[z42]

Please tell me that one had punctuation!

Please go and see for yourself and see what you think however before you jump there and start reading you might want to prepare yourself by reading say episode 18 of the literature classic James Joyce Ulysses see here for a link Ulysses by James Joyce: Episode 18 - Penelope that shows that punctuation is overrated anyway and is only a crutch used by lightweights good luck and have fun although one can of course debate the literary quality of a 9 page long internet forum thread about aircraft guns versus what is ostensibly a shining example of modernist literature but that's up to the reader to decide it's all relative anyway as James Joyce himself might have very well been aware as Einstein had published the general theory of relativity in 1915 a few years before Ulysses was published so relativity was on everybody's mind back then as it was a big change in how people thought about mankind's place in the universe and everything.

 

[Thumpalumpacus]

Please go and see for yourself and see what you think however before you jump there and start reading you might want to prepare yourself by reading say episode 18 of the literature classic James Joyce Ulysses see here for a link Ulysses by James Joyce: Episode 18 - Penelope that shows that punctuation is overrated anyway and is only a crutch used by lightweights good luck and have fun although one can of course debate the literary quality of a 9 page long internet forum thread about aircraft guns versus what is ostensibly a shining example of modernist literature but that's up to the reader to decide it's all relative anyway as James Joyce himself might have very well been aware as Einstein had published the general theory of relativity in 1915 a few years before Ulysses was published so relativity was on everybody's mind back then as it was a big change in how people thought about mankind's place in the universe and everything.

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