# Spitfire Armaments



## wuzak (Apr 3, 2014)

Suppose the production of the Hispano 20mm cannon ran into problems and/or its operational performance was way below what the RAF could accept, what would be done with the Spitfire's gun arrangements?

I assume that the universal wing, which could take 4 x 20mm cannon, 2 x 20mm + 4 x 0.303" or 8 x 0.303", could be adopted to take the Browning 0.50" HMG in the cannon bays.

But would they?

What other cannon options were available to the British around 1941/42?

If they did adopt the 0.50" HMG for the Spitfire, in what combinations would it be used?

4 x 0.50"
4 x 0.50" + 2 or 4 x 0.303"
2 X 0.50" + 4 x 0.303"

The elimination of the long barrels would have boosted performance by a small amount.


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## tomo pauk (Apr 3, 2014)

Until a two stage Merlin or any Griffon is available, use 4 .50s. After that, six should be used? 

Other options, available in different years:
Copy the ShVAK (offer some money to the Finns for captured examples, or demand the blueprints and samples from the Soviets once the Germans attack them). 
Copy the MG FF and/or MG-151. 
Necked-up the .50 to produce a 15-18 mm cannon. 
Copy the Breda SAFAT; having the guns in the wing solves the low synchronized RoF; neck it up to have a cannon. 
Start talking with Oerlikon early enough. 
Try fitting the ground-based Oerlikon in the wings, as maybe the worse of those options.


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## Jabberwocky (Apr 3, 2014)

If the RAF had foreknowledge of irresolvable problems with the 20 mm Hispano, then the best option would have been licenced production of the FN 13.2x99 HMG.

This was a lightened version of the M2 Browinging (about 5 kg lighter) adopted for the fractionally larger and heavier 13.2x99 Hotchkiss round (otherwise identical to the 12.7x99) firing at 1000 rpm, at slightly reduced velocity (810-820 m/sec compared to 850-880 m/sec).

4 x 13.2 HMGs would have offered more power than eight .303s, at roughly the same weight.


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## wuzak (Apr 3, 2014)

tomo pauk said:


> Until a two stage Merlin or any Griffon is available, use 4 .50s. After that, six should be used?
> 
> Other options, available in different years:
> Copy the ShVAK (offer some money to the Finns for captured examples, or demand the blueprints and samples from the Soviets once the Germans attack them).
> ...



Would 6 x 0.50" HMGs require a redesign of the Spitfire wing, or could the 0.50" fit in one of the outer 0.303" bays?

I seem to recall that early cannon fighter proposals suggested the Oerlikon. I was under the impression that the Oerlikon was passed over in favour of the Hispano, rather than it being late.


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## HBPencil (Apr 3, 2014)

wuzak said:


> Would 6 x 0.50" HMGs require a redesign of the Spitfire wing, or could the 0.50" fit in one of the outer 0.303" bays?



I suspect they wouldn't fit in the 0.303 bays... but it's interesting because it raises the question, for me at least, if they would have even designed the universal C wing as they did if the RAF didn't have Hispanos to put in 'em.


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## Shortround6 (Apr 3, 2014)

tomo pauk said:


> Other options, available in different years:
> Copy the ShVAK (offer some money to the Finns for captured examples, or demand the blueprints and samples from the Soviets once the Germans attack them).



Like many things, could take 1 to 2 years to get into production, especially if you have to reverse engineer it. 



> Copy the MG FF and/or MG-151.



Two different situations as the MG FF (or it's equivalent) had been on the open market since the early 30s. British looked at the MG-151 and thought it took too much machining. 



> Necked-up the .50 to produce a 15-18 mm cannon.



Perhaps but you get into diminishing returns very quickly as you go down in caliber for HE shells. Weight of projectile for similar shape varies with the cube of the diameter (roughly). An 18mm shell might only be 65% of the weight of 20mm (83 grams?) German 15mm HET weighed 57 grams compared to more 'normal' 120-130 grams for 20mm shells. Change type of projectile or shape and things can very considerably. 
American .50 cal ammo has a base diameter of 20.3mm (diameter of case just in front of rim).
Russian 12.7mm ammo has a base diameter of 21.8mm. 
Most straight 20mm rounds had base diameters of 21.8-22mm. 
Most of the heavier 20mm shells had around 10 grams of HE 
The German 15mm had 2.8 grams HE ( in part because it also had a tracer element) 



> Copy the Breda SAFAT; having the guns in the wing solves the low synchronized RoF; neck it up to have a cannon.



This one isn't even close, the 12.7mm Breda SAFAT used a cartridge almost identical to the British .5in machine gun round. British have two much better options, use the .5 Vickers sort of as is, reliability being a bit of a problem or just scale the Browning action to use the .5 cartridge for a British version of the Japanese Ho-103 machine gun. 







From Tony Williams excellent site. 

The 12.7 x 81 case just isn't big enough to neck up to much. 



> Start talking with Oerlikon early enough.
> Try fitting the ground-based Oerlikon in the wings, as maybe the worse of those options.



The Oerlikon guns are not fast firing without a lot of work and may have more trouble converting to belt feed. The Japanese did mange both but it took a while.


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## wuzak (Apr 4, 2014)

Jabberwocky said:


> If the RAF had foreknowledge of irresolvable problems with the 20 mm Hispano, then the best option would have been licenced production of the FN 13.2x99 HMG.
> 
> This was a lightened version of the M2 Browinging (about 5 kg lighter) adopted for the fractionally larger and heavier 13.2x99 Hotchkiss round (otherwise identical to the 12.7x99) firing at 1000 rpm, at slightly reduced velocity (810-820 m/sec compared to 850-880 m/sec).
> 
> 4 x 13.2 HMGs would have offered more power than eight .303s, at roughly the same weight.



Were FNs built anywhere outside of Belgium?


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## Juha (Apr 4, 2014)

Swedish AF used 13,2mm HMG during the war, my bet is that they also produced it.


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## tomo pauk (Apr 4, 2014)

Good call on the Belgian HMG.



HBPencil said:


> I suspect they wouldn't fit in the 0.303 bays... but it's interesting because it raises the question, for me at least, if they would have even designed the universal C wing as they did if the RAF didn't have Hispanos to put in 'em.



IIRC, the mock-up installation of six Hispanos was tried on the Spitfire.



Shortround6 said:


> Like many things, could take 1 to 2 years to get into production, especially if you have to reverse engineer it.



Agreed.



> Two different situations as the MG FF (or it's equivalent) had been on the open market since the early 30s. British looked at the MG-151 and thought it took too much machining.



Agreed re. MG FF.
In case the RAF badly wants a cannon, but there are no Hispanos around (or anything cheaper), the machining would be applied to copy the MG-151. We can have Hurricanes with maybe only two 'MG-151' plus 4 Brownings etc.



> Perhaps but you get into diminishing returns very quickly as you go down in caliber for HE shells. Weight of projectile for similar shape varies with the cube of the diameter (roughly). An 18mm shell might only be 65% of the weight of 20mm (83 grams?) German 15mm HET weighed 57 grams compared to more 'normal' 120-130 grams for 20mm shells. Change type of projectile or shape and things can very considerably.



The 80-85 gram HE trumps the multiple .303 rounds. Having four of such cannons should at least equal the typical Spitfire battery (2 Hisso + 4 .303s). The cannon ammo load per barrel would be increased at least 50% from Spit's 120 rpg. 



> American .50 cal ammo has a base diameter of 20.3mm (diameter of case just in front of rim).
> Russian 12.7mm ammo has a base diameter of 21.8mm.
> Most straight 20mm rounds had base diameters of 21.8-22mm.
> Most of the heavier 20mm shells had around 10 grams of HE
> The German 15mm had 2.8 grams HE ( in part because it also had a tracer element)


 
Thanks for the data. 



> This one isn't even close, the 12.7mm Breda SAFAT used a cartridge almost identical to the British .5in machine gun round. British have two much better options, use the .5 Vickers sort of as is, reliability being a bit of a problem or just scale the Browning action to use the .5 cartridge for a British version of the Japanese Ho-103 machine gun.
> From Tony Williams excellent site.
> The 12.7 x 81 case just isn't big enough to neck up to much.



Agreed. Must admit that I've overlooked the .5 Vickers.




> The Oerlikon guns are not fast firing without a lot of work and may have more trouble converting to belt feed. The Japanese did mange both but it took a while.



It is again the case of whether RAF badly wants the cannon or not. The Oerlikon FF seem like decent weapon (Wikipedia; usual disclaimer applies):
_The original "FF" used a slightly upgraded 128 gram 20x72mm round with a muzzle velocity of 600 m/s at a cyclic rate of 520 rounds per minute, almost double that of the original F and AF models._

The MV is a bit lacking, though. 
The Ikaria MG FF was the German derivative? The Germans managed to come up with a 90-rd drum, such was used on the Fw-190. But I agree that a belt fed cannon is a better thing.


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## wuzak (Apr 4, 2014)

I found another potential cannon candidate - one that was considered for aircraft used by the Air Ministry, and considered for the Spitfire.

The Vickers 25.4mm cannon



> The Spitfire connection
> In "Spitfire, the History" by Morgan and Shacklady (Key Publishing Ltd, 1987) there is on page 61 a table of alternative armaments proposed for the Spitfire during its design/development phase. Included in these (rather surprisingly) is a 25.4mm Vickers. The data quoted for it match up almost exactly with the 25x189 gun and ammunition: a shell weight of .551 lbs (250 g); a muzzle velocity of 3,000 fps (914 m/s); a gun weight of 127 kg; and a length of 259 cm.


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## wuzak (Apr 4, 2014)

double post


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## Shortround6 (Apr 4, 2014)

Rates of fire and projectile size have to be looked at. British .303, once they got production up, had an incendiary round with about 1 gram of material in it. With two guns delivering 40 rounds per second that is 40 grams per second of incendiary materiel for about 20-24 GK worth of guns and ammo at under 3kg per hundred.

Most countries seemed to get too tricky with .5in/12.7mm ammo and often had a variety of "multi-purpose" ammo which makes one wonder how good they were at any one thing. for example and again from Tony Williams excellent website






From left to right;
Ball with lead and aluminium filling.
API with incendiary filling (white phosphorous in the bullet tip). 
APIT (Armor piercing incendiary tracer)
HEIT (High explosive incendiary tracer (?) 

One can see a number of compromises and problems. Placing the incendiary compound in the bullet tip gives a good indication of bullet strikes and may work pretty good on fabric covered aircraft. It may not work so well on all metal aircraft as the incendiary compound gets stripped away on impact and does not penetrate very far into the aircraft. The _triple_ threat APIT begins to show problems, the AP core is reduced in size and weigh resulting in less armor penetration. The incendiary compound in the nose is much reduced in size (good strike indicator?) to accommodate the tracer element in the rear although tracer element may contribute to incendiary effect _inside_ aircraft. Round #4 shows a few more problems, one is that decent fuses can only be made so small and take up a disproportionate amount of room inside small projectiles. 2nd is that trying to combine HE rounds with tracer cuts into the HE capacity rather severely. Round #4 is carrying 0.8 grams of Penthrite wax. 

Ammo weight has gone up to around 10.7kg per hundred in links. American .50 cal can weigh 13.9kg in links. 

Slow firing 20mm cannon pack a punch when the shell lands but they weigh over twice as much as a .303 gun (even for a very light 20mm) and the drums are not light either. One 20mm gun listed weights of empty drums as 9kg for a 45 round, 10 kg for a 60 round, 12kg for a 75 round and 13kg for 100 round, ammo was 240 grams per round. 

A big part of this question is _when_? Summer of 1940 and the Hispano proves to be crap and the British are scrambling not only for the Spitfire but for ALL their future fighters? 1938 when they still have time to do something?


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## fastmongrel (Apr 4, 2014)

Madsen made 20mm and 23mm guns for aircraft use. There is also the BESA 15mm. I know nothing about rates of fire or weight maybe someone has the figures.


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## tomo pauk (Apr 4, 2014)

Good post, SR6.

There might not be much of a reason for the ~30g projectile to mess around with a complicated and expensive fuzes, indeed. Hence my proposal for necking out HMG cartridges, so a more worthwhile HE content might be carried.



> Slow firing 20mm cannon pack a punch when the shell lands but they weigh over twice as much as a .303 gun (even for a very light 20mm) and the drums are not light either. One 20mm gun listed weights of empty drums as 9kg for a 45 round, 10 kg for a 60 round, 12kg for a 75 round and 13kg for 100 round, ammo was 240 grams per round.



All fine; the 20mm ammo weighting 240 g is for the 'hi-power' suff, like Hispano. The MG-FFM was at ~180g ('regular' shell) or at ~160g (mine shell - maybe the Allies might adopt that, too?). The MG-151/20 was at 180g (mine shell) and 202 g ('regular' shell). The necked-out cartridge (17-18 mm) weight should be in the ball park with MG-FFM with mine shell. Not as destructive, but having four such canons should more than make up for that.



> A big part of this question is when? Summer of 1940 and the Hispano proves to be crap and the British are scrambling not only for the Spitfire but for ALL their future fighters? 1938 when they still have time to do something?



Not sure - whether it is the original Hispano, or British Hispano, that enters into problems and/or RAF is not satisfied with:

_Suppose the production of the Hispano 20mm cannon ran into problems and/or its operational performance was way below what the RAF could accept, what would be done with the Spitfire's gun arrangements?_

Wuzak? 

BTW: this seems like a good reading: http://www.ibiblio.org/hyperwar/USN/ref/MG/index.html


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## wuzak (Apr 4, 2014)

Shortround6 said:


> A big part of this question is _when_? Summer of 1940 and the Hispano proves to be crap and the British are scrambling not only for the Spitfire but for ALL their future fighters? 1938 when they still have time to do something?



My original premise was that the Hispano made it into production and into the Spitfiree, such that the universal wing has been designed, when it is discovered that it isn't working as required (ie it is crap). So, basically, late 1940.

I would think that the problems with the Hispano would be solved - eventually. But, in the mean time, the British have to find alternatives - and quickly.


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## Shortround6 (Apr 4, 2014)

British are pretty much stuck then. Perhaps they can get a few thousand .50s from the US but with no production line set up any of the foreign cannon or MG alternatives are many months (or years) away from service use. Even trying to adapt the .5 Vickers gun could take several months and perhaps not be very successful in the end. 

Stick in the eight .303s and make all the incendiary ammunition you can.

BTW, the Hurricane II and Typhoon are stuck with twelve .303s and the Beaufighter and Whirlwind are armed ????????


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## Greyman (Apr 4, 2014)

There was a 12-Browning installation built and tested by Martin Baker for the Whirlwind in case the Hispano didn't pan out.


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## Glider (Apr 4, 2014)

I like the idea of putting the 15mm BESA into the frame as a stand by. It was automatic, belt fed, in production and designed as an anti tank gun so power and penetration shouldn't be a problem but had a slow ROF 430 rpm. If you could work on the ROF it has some potential


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## Juha (Apr 4, 2014)

BESA 15mm wasn't a success asan automatic AFV cannon/HMG, in automatic fire the barrel vibrated and so ruined the accuracy so it was mainly used as a single shot weapon. So at least as turret weapon it was a lousy automatic gun.

Juha


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## fastmongrel (Apr 5, 2014)

Juha said:


> BESA 15mm wasn't a success asan automatic AFV cannon/HMG, in automatic fire the barrel vibrated and so ruined the accuracy so it was mainly used as a single shot weapon. So at least as turret weapon it was a lousy automatic gun.
> 
> Juha



The 7.92 BESA was noted for its accuracy so there is nothing fundamentally wrong with the gun, the barrel looks very long so maybe it isnt supported properly. Vickers produced for trials purposes a HMG version of the Vickers K .303 in 13.2x99 the Vickers K was very reliable so maybe that was an option if it is built in 12.7x87. 

All these options need the RAF to have 20/20 foresight as building a production line takes a long time I would say at the very least a HMG or Cannon replacement for the Hispano needs to be started in 1938 and even then it probably wouldnt be ready any earlier than a Hispano.


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## wuzak (Apr 5, 2014)

So, as a stop gap measure Spitfires would have to be armed with Browning M2 0.50" HMGs?

But how many - 2, 4? Can they fit 6 in the universal wing?

If they use 4 x 0.50" HMGs, would they keep the 4 x 0.303"s as well?


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## Glider (Apr 5, 2014)

As to the number of 0.5 in a Spitfire I would expect 4 would be expected for the early Mk I and II and 6 in the universal wing. As to the 0.3.3 my guess would be no. The RAF recognised that 4 x 0.5 was at least as good as 8 x 303 and that extra would be added weight with little gain. When you get to the E wing then 6 x 0.5 shouldn't be a problem.


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## wuzak (Apr 5, 2014)

I can see where 4 x 0.50" HMGs would go in the E-wing - that is, in the cannon bays (of which there were 4) - but where do you put the extra 2? The 0.303" bays in the E-wing were, from my understanding, blanked off. Perhaps on the fuselage and synchronised?


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## Shortround6 (Apr 5, 2014)

Sort of depends on _exactly_ when the 20mm Hispano drops in the crapper as the "C" wing was a little late in coming. The "B" wing was limited to three gun bays and was fitted to some MK IIs and some MK Vs still had A wings and some had B wings. 
I am not sure if you could stick a .50 in the outer machine gun bay. The next inboard bay seems to have the length and height may be able to be taken care of with a blister if needed. 

Trying for six .50s gets you into the American problem. The .50 was not only a heavy gun, it's ammo was heavy. The 1400 rounds of .303 ammo for the four outboard .303s weigh as much as 300 rounds of .50 cal ammo. 

To be more accurate the weight of the guns and ammo in Spitfire with 2 20mm and 120 rounds of cannon ammo per gun was 649.5lbs. 205.5lbs for the .303s and 444lbs for the cannon. A P-40E with six .50s had a 470-480lb gun installation and another 423lbs worth of ammo and that allowed 235 rounds per gun from a total of around 900lbs, ammo boxes, gun heaters, etc not included for either. Please note that a six .50 battery with 235 rpg weighs very close to a four 20mm Hispano battery and would ahve a simialr effect (except perhaps barrel drag) on performance and handling.

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## fastmongrel (Apr 5, 2014)

Shortround6 said:


> To be more accurate the weight of the guns and ammo in Spitfire with 2 20mm and 120 rounds of cannon ammo per gun was 649.5lbs. 205.5lbs for the .303s and 444lbs for the cannon. A P-40E with six .50s had a 470-480lb gun installation and another 423lbs worth of ammo and that allowed 235 rounds per gun from a total of around 900lbs, ammo boxes, gun heaters, etc not included for either. Please note that a six .50 battery with 235 rpg weighs very close to a four 20mm Hispano battery and would ahve a simialr effect (except perhaps barrel drag) on performance and handling.



As you have mentioned several times in other threads the .50 Browning pre 1940 isnt the same as a post 1940 Browning so the 1940 4 x .50s isnt quite what the Mustang carried in 43 as far as weight of fire and reliability.


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## yulzari (Apr 5, 2014)

2x40mm S guns in belt fed form in Tornado/Typhoon and twins.

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## fastmongrel (Apr 5, 2014)

yulzari said:


> 2x40mm S guns in belt fed form in Tornado/Typhoon and twins.



Nic idea but a bit slow firing for a fighter even though one hit would drop pretty much anything.


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## stona (Apr 5, 2014)

There were of course unforeseen problems fitting the .50 calibre machine gun next to the cannon.








There are also problems which can be anticipated. Time and again I see people glibly banging on about adding this, that or the other armament or even 'redesigning the Spitfire wing' without the vaguest concept of just what that might entail. 

Cheers

Steve

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## Glider (Apr 5, 2014)

wuzak said:


> I can see where 4 x 0.50" HMGs would go in the E-wing - that is, in the cannon bays (of which there were 4) - but where do you put the extra 2? The 0.303" bays in the E-wing were, from my understanding, blanked off. Perhaps on the fuselage and synchronised?



The E winq contained 2 x 20mm and 2 x 0.5, so working on the basis that you can fit 2 x 0.5 into the space occupied by one 20mm, that leaves you 6 x 0.5


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## wuzak (Apr 5, 2014)

Glider said:


> The E winq contained 2 x 20mm and 2 x 0.5, so working on the basis that you can fit 2 x 0.5 into the space occupied by one 20mm, that leaves you 6 x 0.5



I don't think you can fit 2 x 0.50"in the space for a 20mm.


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## Shortround6 (Apr 5, 2014)

You can't fit two .50s into the _space_ of one 20mm cannon. 

Unless somebody can find not only width of the receivers but the space needed for feeds and ejection. 

Here is a picture of a P-51D gun bay






P-51C gun bay


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## Aozora (Apr 5, 2014)

Here is the E wing layout:






Note that the ammunition for the .50 cal was inboard, meaning that it had to be guided under the Hispano


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## wuzak (Apr 5, 2014)

stona said:


> There were of course unforeseen problems fitting the .50 calibre machine gun next to the cannon.
> 
> 
> 
> ...



I take it that is a trials aircraft?

Did it adamage the barrel of the 20mm or only the shroud?


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## Shortround6 (Apr 5, 2014)

Aozora said:


> Note that the ammunition for the .50 cal was inboard, meaning that it had to be guided under the Hispano



I believe it was out board but in any case it went under. 

Photo of the two guns installed in the wing certainly shows that TWO .50s will NOT fit in the space of one 20mm. Thank you/


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## wuzak (Apr 5, 2014)

The next question is, can 6 x 0.50" (0r 8!) be fitted to the universal wing, using the 0.303" bays for 0.50"s?


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## stona (Apr 6, 2014)

wuzak said:


> I take it that is a trials aircraft?



BS118 at Worthy Down. See Aozora's post above.

I've not read the report to which the photo is an appendage, but the damage looks to be to the fairing.

Cheers

Steve


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## Shortround6 (Apr 6, 2014)

wuzak said:


> The next question is, can 6 x 0.50" (0r 8!) be fitted to the universal wing, using the 0.303" bays for 0.50"s?



You can probably fit 4 into the cannon bays and 2 more into the inner machine gun bays, fitting into the outer machine gun bays may be possible, difficulty may be depth rather than length or width and yes you could probably uses bulges for height.

Now the question is why (especially eight guns)? as shown in previous post 6 .50s with 235 rpg weigh about as much as 4 20mm with 120rpg and there is some question about the performance penalty of the early 4 cannon Spitfires. 

Trying for 8 guns gives you 573lbs worth of guns alone and 125rpg (about 10 seconds worth) adds another 300lbs for 873lbs or over 220lbs more than the "normal" C wing armament.


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## wuzak (Apr 6, 2014)

Why 6 or 8? I guess the question is are 4 x 0.50" HMGs sufficient? I suppose going into 1941 the opposition for day bombers in the UK will be mainly fighter-bomber types, rather than bombers with heavier armour.

Also, they are replacing their cannons with 2nd or 3rd best choice. There have been many debates on this site as to the comparison between the destructive power of the 20mm Hispano vs the 0.50" Browning. Some suggest that the Hispano was 3 times as effective as the 0.50", so replacing the two 20mm would require 6 0.50"s for equivalent effectiveness.

Remembering that the first few Kittyhawk Is had 4 x 0.50", but later ones had 6 x 0.50". And the P-51 went from 4 in the -B to 6 in the -D.


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## stona (Apr 6, 2014)

Only the US stuck with machine guns, and then not for long, though too long. In Korea the F-86 still had machine guns against the Mig-15's cannon (one of which was a 37mm). Good job the US pilots , for a variety of reasons, went through John Boyd's famous OODA (observation, orientation, decision, action) a lot quicker 
Cheers
Steve


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## swampyankee (Apr 6, 2014)

wuzak said:


> Why 6 or 8? I guess the question is are 4 x 0.50" HMGs sufficient? I suppose going into 1941 the opposition for day bombers in the UK will be mainly fighter-bomber types, rather than bombers with heavier armour.
> 
> Also, they are replacing their cannons with 2nd or 3rd best choice. There have been many debates on this site as to the comparison between the destructive power of the 20mm Hispano vs the 0.50" Browning. Some suggest that the Hispano was 3 times as effective as the 0.50", so replacing the two 20mm would require 6 0.50"s for equivalent effectiveness.
> 
> Remembering that the first few Kittyhawk Is had 4 x 0.50", but later ones had 6 x 0.50". And the P-51 went from 4 in the -B to 6 in the -D.




The _USN_ found the 20mm Hispano to be roughly 3 times as effective as the 0.5 in Browning. The problem the US had with the Hispano was in actually building it in quantity.


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## tomo pauk (Apr 6, 2014)

The US have had problem with quality of Hispanos they were producing, not with quantity. Wikipedia article references that with the book available here.


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## tomo pauk (Apr 6, 2014)

wuzak said:


> Why 6 or 8? I guess the question is are 4 x 0.50" HMGs sufficient? I suppose going into 1941 the opposition for day bombers in the UK will be mainly fighter-bomber types, rather than bombers with heavier armour.
> 
> Also, they are replacing their cannons with 2nd or 3rd best choice. There have been many debates on this site as to the comparison between the destructive power of the 20mm Hispano vs the 0.50" Browning. Some suggest that the Hispano was 3 times as effective as the 0.50", so replacing the two 20mm would require 6 0.50"s for equivalent effectiveness.
> 
> Remembering that the first few Kittyhawk Is had 4 x 0.50", but later ones had 6 x 0.50". And the P-51 went from 4 in the -B to 6 in the -D.



Once engine power is sufficiently up (two-stage Merlin, any Griffon), the 6 HMGs should not be that a problem. 
The 1st P-40s (Tomahawks) were using 4 LMGs in the wing. Wing endured slight modifications (weight cost ~100-120 lbs) so it can have installed 6 HMGs and their ammo. The P-51 went from 4 LMGs and 2 HMGs to all 6 HMGs in the P-51D. Also carried 4 Hispanos, of course.


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## Glider (Apr 6, 2014)

Shortround6 said:


> I believe it was out board but in any case it went under.
> 
> Photo of the two guns installed in the wing certainly shows that TWO .50s will NOT fit in the space of one 20mm. Thank you/



I admit my comment was based on the Hurricane. If with a bit of imagination they could squeeze 2 x 20mm into a space that originally held 4 x 0.303 I was thinking that they might be able to do the same with putting 2 x 0.5 into 1 x 20mm. My mistake


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## Jonnyboy369 (Dec 14, 2015)

Was not the original 8 .303 browning armament actually highly effective? I have watched so much old gun camera footage. The German bombers looked like they were being shredded by the high volume 7.7 rounds , so much camera footage just shows them coming apart. Also, when I see early me-109 footage firing on a spitfire, it is usually them missing completely with the slow firing low velocity drum fed early mg/ff 20 MMS. This subject has intrigued me for years. Also in this footage, it looks like the German mine shells are just bursting to little effect when they hit. I can't imagine even a modern aircraft standing up to 9,600 rounds per minute of rifle caliber ammo. Just my thought .


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## Greyman (Dec 15, 2015)

Jonnyboy369 said:


> Was not the original 8 .303 browning armament actually highly effective? I have watched so much old gun camera footage. The German bombers looked like they were being shredded by the high volume 7.7 rounds , so much camera footage just shows them coming apart. Also, when I see early me-109 footage firing on a spitfire, it is usually them missing completely with the slow firing low velocity drum fed early mg/ff 20 MMS. This subject has intrigued me for years. Also in this footage, it looks like the German mine shells are just bursting to little effect when they hit. I can't imagine even a modern aircraft standing up to 9,600 rounds per minute of rifle caliber ammo. Just my thought .



Eight .303-inch Brownings could certainly be devastating - but the type of target really comes into play. Also, 9,600 rounds per minute is certainly impressive - but holding a target in a proper gun solution for enough time to build up a lethal density is a more important question.

Going by a handful of gun camera films isn't really a scientific approach. Sample size is a primary issue. Judging damage from a few frames of grainy footage is a bad idea. A superficially devastating round could do little damage, while a round that discretely impacted between picture frames could do devastating internal damage with no apparent effect (eg: kill the pilot).

Your observations on the German 20-mm vs. Browning .303-inch are certainly reasonable. Point-form summation would be; easier to hit with Browning battery, better results from a hit with a 20-mm. Jabs versus haymaker.

20-mm explosions or the results thereof might not always look too impressive but keep in mind the hail of invisible (to the camera) fragments being sprayed inside the targeted aircraft.

That said - the British were critical of their own early 20-mm Hispano fuzes and early Luftwaffe fuzes for detonating too early (on the aircraft skin), wasting much of their effect.


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## stona (Dec 15, 2015)

The decision to adopt the eight gun fighter, with eight rifle calibre machine guns, was based on considerable research. It was estimated that given the short firing time a pilot would get at the new high speeds of engagement eight guns would be required to deliver a lethal weight of fire. This worked in the mid to late thirties, but early in the war the Luftwaffe started fitting ever increasing amounts of armour to its aircraft, bombers in particular, which negated the earlier calculations. There are reports of bombers returning to bases in France with literally hundreds of .303 strikes. 
The adoption of cannon armament became a priority for the RAF/Air Ministry. The story of the problems with early installations in the Spitfire is well known, but was initially a stop gap solution. The plan was to lift four cannon with a single engine fighter, the Hawker fighter that would become the Typhoon, but that too had well known development problems and never replaced the Spitfire in the fighter role. It meant a reprieve of sorts for the Whirlwind, but that was never going to be a solution in the long term, sorting out the Spitfire was.
Cheers
Steve


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## stona (Dec 15, 2015)

I'd add that research continued throughout the war. So called 'Lethality and Vulnerability Testing' was carried out at Orford Ness throughout the war. Orford Ness is better known as the station where the early RDF research was carried out before the war and where the ballistic testing of Britain's atomic bomb were carried out post war.

The 'Lethality and Vulnerability Testing' is best explained by Bert Smith, an RAF fitter, posted to Orford Ness from an operational squadron in 1942. The pupose of the testing was,

_"...to attack captured enemy aircraft with our airborne weapons and our aircraft with the enemy's airborne weapons, the results providing essential data for those responsible for identifying and meeting the operational needs of the Service. At its simplest, a trial could be carried out with just a gun and a target, but additional information such as velocity and altitude of the projectile on impact, potential to inflict damage or injury on impact, effects of slipstream etc., might also be required. Sometimes high speed photography would be used to record the sequence of events after impact." 
_

They certainly investigated the effects of shrapnel, particularly relevant after the invention of proximity fuses. They also investigated the internal fragmentation (spalling) characteristic of armoured plate or windscreens. Some supposedly bullet proof materials actually caused worse injuries to aircrews. Out of date London telephone directories were used to measure penetration!

Penetration of fuel tanks and other vulnerable areas was investigated. Fuel tanks were more likely to rupture when struck by an unstable round, the greater the yaw the worse the damage. It was discovered that simply wrapping high pressure oxygen cylinders with a layer of wire virtually eliminated any tendency to rupture.

This operational research is a topic in itself. The RAF, more than any other Service, was keen to take the advice of the 'boffins' (a term coined at Orford Ness). It was a relatively new service and employed the cutting edge technology of the day. It needed all the help it could get 

Cheers

Steve

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## Zipper730 (Mar 24, 2018)

fastmongrel said:


> Madsen made 20mm and 23mm guns for aircraft use. There is also the BESA 15mm. I know nothing about rates of fire or weight maybe someone has the figures.


From what I read doing some searches (today actually)...

Madsen 20
Muzzle Velocity: 900 m/s
Refire: 400-500 rpm

Madsen 23
Muzzle Velocity: 720 m/s
Refire: 400 rpm


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