.50 cals on Spitfires

[tail end charlie]

I agree that 20mm rounds is better over all, and history proves it. I wonder how A Spit Mk I or II would have performed with 4x .50cals vs 8x.303.cals vs bombers and fighters. The .50cal weighs almost 4x the .30 cal, so gun weight would double. but the volume of the .50 cal is not much more. The cartridge itself is 67% larger than the .30-06 that the US used(exactly, as it was just blown up in scale from the rifle round)

How many rounds did the Spit I carry per gun?
How much lead weight could be put by the 8x.303s in a typical burst(0,5 to 1 sec?)
What is the same number for 4x.50cals?
Late war spits carried 250 rds of .50cals. How do the weight of 4x.50cals w/250 rds compare to weight of 8x.303 with their ammo?
Would the extra weight(if any) hamper the Spit in a dogfight with the Bf-109E?
Would the heavier leadweight of the .50cal battery(if any) be more effective in bringing down the light/medium bombers of the day(BoB), the He-111, Do-17 and Ju-88?

I know the Armour Piercing qualities of the .50cal way surpasses the .303, but I'm curious on a more holistic level, on how the Spit would fare with another existing and working gun of the time, before the HS 20mm were up to snuff.

Zajuts

The link I gave earlier gave a lot of info, there are a lot of other linked pages explaining the ins and outs and various opinions. there were different rounds for each gun and different problems with each, all made worse in the spitfires case by the very thin wings. Whereas the Hurricane easily accomodated 4 machine guns close together the spitfire had them spread along the wings.

 

[Shortround6]

Part of the problem when changing from 8 .303s with 300-350 rpg to American .50 cal guns is the weight.
The weight of the American .50 cal is on the order over twice as heavy per gun. Perhaps as much as 2.9 times as heavy. The Belgian 13.2mm version which went into a few Hurricanes weighed 24 kg compared to the Browning .303s 10 KG.
The next problem is ammo weight. American .50 cal ammo is on the order of 5 times as heavy as .303 ammo. Changing from 8 . 303 guns with 300rpg (early Spitifire and worst case) to 4 American .50s is going to leave you with under 100 rounds of ammo per gun on a strict weight for weight basis. And that is using the 24 kg for the Belgian guns. How much performance are you willing to trade the extra ammo? an extra 400 rounds (100 per gun for 4 guns ) weighs 120lbs.

Next question is when is the decision to be made. for most of the 30s the American .50 fired at 600rpm unsynchronized. It was only right before the war the the rate of fire was boosted to 800-900rpm. So you might be comparing 160 .303 bullets a second to 40 .50cal bullets a second. For the faster firing guns it gets up to a about 56 .50 cal bullets per second but you need 210 rounds per gun to get the combat duration of the Spitfire with it's 300rpg.

You can't do ANY damage if you don't hit.
20mm make up for lack of hits with lots of damage per hit.
U.S. .50cal is stuck between. Limited damage per hit unless something hard is hit. Limited amount of hits in a small battery with limited ammo.

Remember that MK I spitfires and MK I Hurricanes only had 880hp for take off and under 1000hp for climb without running at full throttle. later models with much more power could carry heavier armament.

 

[looney]

In short: yes they considered the .50 but the overall effectivenes was to minimal compared to a cannon armed spit

 

[zajuts149]

Thanks a lot, Colin1!!

 

[zajuts149]

Part of the problem when changing from 8 .303s with 300-350 rpg to American .50 cal guns is the weight.
The weight of the American .50 cal is on the order over twice as heavy per gun. Perhaps as much as 2.9 times as heavy. The Belgian 13.2mm version which went into a few Hurricanes weighed 24 kg compared to the Browning .303s 10 KG.
The next problem is ammo weight. American .50 cal ammo is on the order of 5 times as heavy as .303 ammo. Changing from 8 . 303 guns with 300rpg (early Spitifire and worst case) to 4 American .50s is going to leave you with under 100 rounds of ammo per gun on a strict weight for weight basis. And that is using the 24 kg for the Belgian guns. How much performance are you willing to trade the extra ammo? an extra 400 rounds (100 per gun for 4 guns ) weighs 120lbs.

Next question is when is the decision to be made. for most of the 30s the American .50 fired at 600rpm unsynchronized. It was only right before the war the the rate of fire was boosted to 800-900rpm. So you might be comparing 160 .303 bullets a second to 40 .50cal bullets a second. For the faster firing guns it gets up to a about 56 .50 cal bullets per second but you need 210 rounds per gun to get the combat duration of the Spitfire with it's 300rpg.

You can't do ANY damage if you don't hit.
20mm make up for lack of hits with lots of damage per hit.
U.S. .50cal is stuck between. Limited damage per hit unless something hard is hit. Limited amount of hits in a small battery with limited ammo.

Remember that MK I spitfires and MK I Hurricanes only had 880hp for take off and under 1000hp for climb without running at full throttle. later models with much more power could carry heavier armament.

Very good points. Just the sort of analysis I had in mind.
I agree totally that the weight issue would be the most critical with the Browning .50cal(Btw. how much different was the Colt .50? same ammo, right?)
If the spit were to retain the same performance, the low ammo stock would hinder it's performance total just as much as low fuel hindered the 109s in BoB.
For shell weight on target, I think 40+ rounds of .50cal would be preferable to 160 rds of .303, as each hit would have 5 times the weight of each .303 bullet. I didn't pursue physics enough in school to calculate the KE here, but I think the effect would be a dramatic improvement in disabling bombers, if one could get enough hits on vital parts like engines...

 

[Colin1]

Thanks a lot, Colin1!!

No worries Z
I should point out my source, which was

Spitfire: The History
Morgan Shacklady

 

[Shortround6]

For shell weight on target, I think 40+ rounds of .50cal would be preferable to 160 rds of .303, as each hit would have 5 times the weight of each .303 bullet. I didn't pursue physics enough in school to calculate the KE here, but I think the effect would be a dramatic improvement in disabling bombers, if one could get enough hits on vital parts like engines...

The .50 cal needs to hit something solid in order for the KE to work. Poking holes in fuselage or wing skinning doesn't cause much more damage than the .303. A 20mm exploding on the skin surface can make a hole around a foot across and several in small area (rear fuselage of Spitfire?) can compromise the strength of a monocoque or semi-monocoque structure. The .50 needs to hit longerons, frames, spars or ribs in order to cause real structural damage. Against fuel tanks the results are much more variable. Self sealing fuel tanks varied widely in construction and effectiveness. The .50 stands a much better chance of bursting a seam on full or nearly full tank than a .303 but if the tank is only part full the shock wave through the fuel has room to dissipate without bursting the tank. A 109 only had one tank so it was never going to be in combat in the BoB with a full tank. Bombers will vary. A hit in the radiator from a .50 means the coolant will leak out a bit faster. Ditto the oil tank/oil cooler. The .50 will punch holes in and stop engines much better than a .303 but even .303s can put holes in the water jackets, crankcases.

The .50 browning was a reliable (for the most part), effective weapon, especially if used in sufficient numbers, but it actually wasn't that efficient of a weapon on a effectiveness to weight ratio.

 

[fastmongrel]

I think the .303 Browning was the wrong gun but the decision to stick with it was the right one at the time. The decision to swap to a .50 has to be made in 1936 and no later, stopping procurement of the .303 Browning and changing to the .50 would cause lots of problems. The factories have to be converted (or built from new) from .303 ammunition to .50 Browning ammunition and sufficent stocks of ammunition have to be built up. Designs for things like mountings have to be redrawn all whilst the Spitfire and Hurricane were being developed I dont know if Hawkers or Supermarine had enough staff at the critical time to swap horses in mid race.

The RAF and most other airforces in 1936 thought the rifle calibre round was sufficent

 

[Glider]

People sometimes are dismissive of the decision to use 8 x 303 on Hurricanes and Spitfires but it compares well against what other airforces were installing in 1938.

RAF 8 x LMG
Luftwaffe 4 x LMG
Japan 2 x LMG
Italy 2 x HMG
Russia 4 x LMG
USA 2 x LMG 2 x HMG
France 1 x 20mm 2 x LMG

Of the above only the MS 406 would be superior. Most countries were experimenting with 20mm but then so was the UK.

 

[Sydhuey]

The RAAF Mk Vlll Spitfires later in the war had there outer 4x .303's replaced with 2x.50 as the .303 was useless for straffing thru jungle canopy and ease of ammo supply from US and the 20MM ammo was in short supply .These Spits had the E wing I believe so the .50 went straight in.
By about 1943 the RAAF realised what a usless weapon the .303 was and was slowly converting all a/c were possible to .50
Beaufighter 6 x wing mounted .303 replaced with 4 x .50
Beaufort 2 x .50 fited to wings and turret guns from .303 to .50 in Mk Vlll
When the Lancaster (replaced with Lincoln) was planned to be build in Australia in 1943 ,RAAF insisted nose and tail turrets to be 2x.50 and top turret 2x20mm, after RAAF aircrew experiance in Europe with Lancaster with .303 and Pacific experiance with B-24 with .50's..

 

[CharlesBronson]

The most ironic thing is that the british had a local 12,7mm design , the Vickers C, not particulary fast firing but belt feed, reliable and far lighter than the Browning.

The Vicker C could be imbedded inside Spitfire wings without the bulge caused by the Hispano but in the end the Spitfire used all foreign designed weapons

 

[Dcazz7606]

Regarding this topic, I'd like to explore a bit the ballistic performance of matching the .303/ 20mm., or .50/ 20mm.on the Spitfire, and or any combo of guns as on the early P-39 Airacobra with had .30/,50 and (20MM. on P-400's) 37MM.(probably used for specific targets and rarely with all guns blazing). Add to this the different types of rounds being fired or whether fired from a deflection position it must have been very difficult to get rounds on target outside of a 6 o'clock attack! Which combo's of guns do you think held the best chance of success of hits ?

 

[gingerbob]

I came rather late to this discussion, but since it has been resurrected fairly recently, I'll chip in.

The RAAF Mk Vlll Spitfires later in the war had there outer 4x .303's replaced with 2x.50

What is your source for that statement? It is the first I've heard of it, and if there is any substantiation I'd sure like to know more! Technically, the Mk.VIII had the 'c' wing, but the 'e' was a modification therefrom, so it certainly could have been done.

To answer the original question, a 6x .50 (or 13.2mm) installation was requested initially in Dec '39 for the proposed Griffon Spit, the Mk.IV, as an alternative to 4x 20mm Hispanos. When the Griffon Spit was put on hold, a trial installation of the former armament was requested for the Mk.III. It wasn't long before the Hispano assumed first priority, perhaps spurred on by the flexibility promised in the Universal (c) wing. The possibility of .50s for the Griffon Spit did linger for some time, one proposal being a different universal wing to take either 6 (or 4) 20mm, or 2 20mm with 4 .50s. Actually the .50 disappeared from consideration for a time, but when it was announced that it could be fitted after all, it completely displaced further consideration of the .303 as an option. The Tempest was also schemed for variability initially, but in 1942 it was decided (separately) that in both cases they could standardize on 4 20mm. This may have been recognition that 4 20mm was a good fighter armament, but it was also in the interest of shaving weight by not providing for more than one installation.

In the RAF the argument of the relative value of .50 vs .303 went on for some time. One factor that finally tipped the balance in favor of the .50 (for the Spit IX/XIV) was the coming gyro gunsight- by greatly increasing accuracy of aim, it much improved the chances of the fewer .50 rounds making contact.

To address the last question, of mixed armaments, it seems a consistent maxim that getting in close gives you the best chances of success, and that would diminish concern about different trajectories, and it would presumably also favor the harder-hitting guns, because you're more likely to actually hit your target, without which no fine-points of different guns matter!

bob

 

[Glider]

As far as I am aware there is no link or dependency, on the introduction of the 0.5 and the development of the gyro gunsight. Is there any documentation to support that anywhere?

 

[gingerbob]

PRO Air 2/2825/109B DOR to SOto CAS, ACAS(TR) 12/1/44 [Note, this is my transcription so I took shortcuts typing. But the meaning is preserved!]
".5 Gun secondary armament in Spitfire
re yours 8/1/44. This history of the proposal to substitute 2 .5" guns for the 4 303 in Spitfires is long and involved and I summarise it as shortly as possible below...

[excerpt:]
12/11/43 Air Ministry replied agreeing that action would be taken to equip Spitfire IX and XIV with .5 as soon as possible, as the result of the trials was likely to be delayed. Further, the change was now considered justified in view of the greatly improved sighting accuracy, as demonstrated by trials just completed, to be expected with the Gyro Gun Sight. Thus, for deflection shooting the .303 would not have the advantage over the .5 which it now has with existing sighting method."

Curiously, it does not appear that fitment of the gyro sight was actually required on 'e' wing aircraft, the two improvements running independently (around the time of D-Day some IXc squadrons had the GGS, while (AFAIK) some IXes did not have it fitted). Perhaps this is partly because the new sight was initially in limited supply, and the Mustang (RAF, or including AAF?) was given priority for it over the Spitfire. I would expect, without having confirmed it, that before long the GGS was going into new Spit IXs, XIVs, and, when they began, XVIs.

bob

 

[Glider]

Thanks for that. IIRC production of the GGS in the UK, was about 1000 a month at the end of the war but only really got going at the end of 1944. Some were used in gun turrets I think everyone wanted a piece of the action.

 

[Edgar Brooks]

The G.G.S. IIC was designed for gun turrets, and controlled by foot pedals; the G.G.S. IID was designed for fighters, and controlled by a twist-grip, on the throttle.
29-5-44 a report stated that 12 IIC sights had been fitted into Lancaster FN.121 turrets for operational trials of GGS only (it was planned to combine them with the Village Inn radar, and Type "Z" infra-red, equipment.)
The same report said that the IID was being fitted retrospectively into the Spitfire IX Seafire III, with approximately 300 100, respectively, having already been fitted. Mustang installation had just started (presumably the Mustang III?) with up to 30 planned for the TAF. Trials were going ahead on the Spitfire XIV XXI (sic.)
It's likely that all low-back Spitfire XVIs had the GGS (note that, until August 1944, it was still known as the IX,) since the "black boxes" had to be fitted before the fuselage fuel tank went in; the low-back XVI was also always "E" armed, because the outer .303" compartments were occupied by compressed-air, and oxygen, tanks, displaced by the fuselage fuel tank.
Swapping from "C" to "E" armament was not a simple thing, since it involved removal of heating and compressed-air pipes, so was supposed to be done only by a factory working party, specially-assigned M.U., or designated member of the Civilian Repair Organisation (there is some evidence of RCAF Squadrons employing DIY, though.)

 

[krieghund]

The .50 cal needs to hit something solid in order for the KE to work. Poking holes in fuselage or wing skinning doesn't cause much more damage than the .303. A 20mm exploding on the skin surface can make a hole around a foot across and several in small area (rear fuselage of Spitfire?) can compromise the strength of a monocoque or semi-monocoque structure. The .50 needs to hit longerons, frames, spars or ribs in order to cause real structural damage. Against fuel tanks the results are much more variable. Self sealing fuel tanks varied widely in construction and effectiveness. The .50 stands a much better chance of bursting a seam on full or nearly full tank than a .303 but if the tank is only part full the shock wave through the fuel has room to dissipate without bursting the tank. A 109 only had one tank so it was never going to be in combat in the BoB with a full tank. Bombers will vary. A hit in the radiator from a .50 means the coolant will leak out a bit faster. Ditto the oil tank/oil cooler. The .50 will punch holes in and stop engines much better than a .303 but even .303s can put holes in the water jackets, crankcases.

The .50 browning was a reliable (for the most part), effective weapon, especially if used in sufficient numbers, but it actually wasn't that efficient of a weapon on a effectiveness to weight ratio.

According to R.Dunn in his book "Exploding Fuel Tanks" the German bombers had an advanced high degree of protection for the fuel tanks. So much so that RAF pilots would aim for the engines/cockpits rather than pepper the wings. There are many stories and pictures of German bombers coming home or ditching looking like Swiss cheese.

During testing of tanks with self sealing (ss) materials surrounding metal tanks it was found that a .50 cal round would cause hydro-static shock enough in the fuel tank to burst the seams if sufficiently full. This was effect was further multiplied if the tanks were rigidly mounted. The .30 cal rounds would not do this.

However, the German bombers employed a bag type suspended by straps in the airframe structure. It was found that this was adequate for .30cal but not .50cal. The ss material had a difficult time sealing the larger holes and of course if the bullet tumbled.....

It is interesting to note that as the BoB was starting the RAF was still in the process of retro-fitting its fighters with ss materials and also to note that many of the Spitfires and Hurricanes left one tank unprotected in the fuselage. Production aircraft had full protection.

The biggest surprise is that the Bf109E's L-shape tank would not get full protection until the end of the battle due to the difficulty with the shape of the tank. The protective bulkhead behind the tank was known to stop .303 rounds.

So IMO arming with .50cal would have greatly increased the RAF's ability to quickly bring down more bombers and less getting away with only damage.

 

[stona]

So IMO arming with .50cal would have greatly increased the RAF's ability to quickly bring down more bombers and less getting away with only damage.

I think that is so. The problem is,with the lower rate of fire and fewer guns,actually hitting the target with the sighting system and pilot training available.

The early gun camera footage from RAF fighters in 1940 revealed not only a tendency for pilots to hugely underestimate deflection angles but also a tendency to open fire at ranges of over 1000 yards which,with just about any machine gun,never mind their .303s,is just a waste of ammunition.

As another poster has already said that the effective combat pilots got in close enough that they would have made effective use of a heavier calibre weapon. The sobering thought is that these men were so rare amongst the thousands of pilots flying in combat on all sides that we know many of their names today.

Cheers

Steve

 

[renrich]

Better gunsights allowed for getting hits at longer ranges thus the need for better ballistic perfomance down range.