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

[z42]

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. So this particular next generation fighter itself didn't happen, and eventually they retrofitted the 20mm to the previous generation fighters (Hurricane and Spitfire). So this waffling about took some time, and it wasn't until mid-war when they got all the issues sorted out and the belt-fed Hispano deployed in numbers. And arguably 20mm was about the best general purpose aircraft armament caliber of the era, and the Hispano was among the best in that class. So in a way it was the entirely right decision.

But all this delay meant that they had to fight the critical early war years with the popgun .303's, with well known issues in needing a huge number of hits to down an enemy plane, particularly multi-engine ones. And as described in this thread here British WW2 Heavy Bomber Armament they never got around to rearming their bombers with anything bigger, partially due to CoG issues in planes originally designed for a .303 defensive armament.

But what if they had instead decided in the mid-30'ies to not skip over the intermediate HMG caliber? Now the big problem with that was that initially Browning wasn't willing to license the M2 to the UK, and the FN slightly improved version of the M2 in didn't really enter production until 1939 or so. But for the sake of argument, lets say the UK signalling interest in a HMG would cause FN to develop their M2 variant earlier and license production to the Brits. What would the effect of such a decision be? Say,

• The UK would have entered the war with HMG equipped fighters. Say, 4 of them on a Hurricane or Spit. Providing longer range and better hitting power particularly against bombers.
• Bombers designed after the mid-30'ies would be designed with a HMG based defensive armament from the start.
• The FN version of the Browning has, per wikipedia, a RoF of 1080 ("standard" and up to 1500 rpm. Providing up to twice the volume of fire in a gun that is even slightly lighter than the Browning AN/M2. Not sure if this 1500 rpm is correct, and what would the barrel wear for such a thing be? But if it's true, then that's pretty impressive.
• FN apparently developed a HE shell for the 13.2mm variant of the MG. Not sure how good such a thing is, I suspect the lower sectional density of a HE shell vs. a solid bullet and the relatively small caliber might mean the ballistics of these shells could be pretty bad?
• Perhaps due to spending all this time on fielding a HMG, the 20mm Hispano would have been delayed and maybe even miss the war entirely. While I do believe the 20mm would be a better gun, maybe the tradeoff of having a HMG available during the critical early years of the war would be worth it vs. lacking a bit of punch in the latter part of the war, when Luftwaffe wasn't in it's prime anymore and it was mostly about fighters and not so much about shooting down bombers by that point.

Thoughts?

 

[tomo pauk]

The HMG-outfitted fighters would've been a boon for the RAF.
Even once the 20mm cannon is perfected, there are still places where the HMG is a better fit due to the smaller size and weight, as well as due to having less heavy and bulky ammo.

I would not put too much of faith in HE ammo for HMGs - IMO, just make a good API round and Bob's your uncle.

 

[pbehn]

The Whirlwind and Typhoon did happen, both armed with 4 x 20mm then came the Beaufighter and Mosquito. The Hurricane and Spitfire started to be fitted with 20mm cannon in 1940 and it was standard fitment on the Mk II Hurricane and Mk V Spitfire in 1941. In 1941 the USA and Germany were still using "pop gun" rifle calibre ammunition and the USA was still having issues with the 50 cal operation during high G manoeuvers in 1943. The RAF downed a lot of planes in the Battle of Britain with their pop guns. My thought is you have just watched a well known Youtube video.

 

[Glider]

For the first part of the war there can be little doubt that 4 x HMG and in particular explosive warheads would have been a big step forward. I think the Italians and Japanese had HE warheads and they worked well.
The problem would be if the Axis had developed a B17 style aircraft, in which case the HMG wouldn't have cut the mustard. A 20mm at least would be required. We know that the didn't, they didn't know it then

 

[Jabberwocky]

• FN apparently developed a HE shell for the 13.2mm variant of the MG. Not sure how good such a thing is, I suspect the lower sectional density of a HE shell vs. a solid bullet and the relatively small caliber might mean the ballistics of these shells could be pretty bad?

Details on 13.2mm ammunition

Ball round:
Projectile weight: 50.8g
Muzzle velocity: 810m/sec

AP round:
Projectile weight: 51.2g
Muzzle velocity: 810m/sec

Tracer round:
Projectile weight: 48.5g
Muzzle velocity: 810m/sec

AP-Tracer:
Projectile weight: 48.9g
Muzzle velocity: 810m/sec

Incendiary:
Projectile weight: 43.8g
Filler weight: 2.9g or 3.2g
Muzzle velocity: 820m/sec

HE round:
Projectile weight: 42g
HE weight: 3.5g
Muzzle velocity: 900m/sec


The HE round on the 13.2mm compares very favourably to other HE rounds in service on HMGs in WW2.
By way of comparison, the Italians and Japanese had about 0.8g to 2g of HE filler in their various 12.7x81 HE rounds.
The Germans had 1.5 to 2g of HE filler in the 13x64 HE rounds they put into service.
The US didn't field an HE round, but they had M8 API with 1 gram of incendiary filler and the M20 incendiary about 1.8 grams. Going from memory, the very late war M23 incendiary had a little under 4 grams of filler.
I can't find details on the 12.7x108 at the moment.

 

[Shortround6]

So this waffling about took some time, and it wasn't until mid-war when they got all the issues sorted out and the belt-fed Hispano deployed in numbers.

Define "waffling about". The British had a signed license agreement in 1937 (?) and a factory under construction in 1938 and the first ceremonial production gun fired in Jan 1939.
Actual production took a bit longer but you can see the overlap on the FN gun.

with well known issues in needing a huge number of hits to down an enemy plane, particularly multi-engine ones

Part of the problem was the lousy ammunition, During the BoB around 3 guns out of eight were being fed ball ammo which was pretty much infantry gun ammo, lead core, light tip, copper jacket or alloy. Didn't penetrate for crap and deflected easily. Two guns out of 8 had AP with steel cores. Depending supply either one or two guns had the good De Wilde ammo.
Now the whole (or large part) of the 13.2mm ammo argument assumes the British (and Americans, they were suppling a fair quantity of the ammo to the British even in 1940) can supply the desired types and quantities of the 13.2mm ammo when they could not supply the existing .303 guns, the Vickers .5in guns and American .50 cal guns with high performance ammo (high performance means better than ball ammo)

FN slightly improved version of the M2 in didn't really enter production until 1939 or so.

I would be a bit leery of enterer production, the British needs high hundreds or thousands of guns per month. Not one hundred per month. How many did FN actually make?

The FN version of the Browning has, per wikipedia, a RoF of 1080 ("standard" and up to 1500 rpm. Providing up to twice the volume of fire in a gun that is even slightly lighter than the Browning AN/M2. Not sure if this 1500 rpm is correct, and what would the barrel wear for such a thing be? But if it's true, then that's pretty impressive.

This brings up one of my own pet peeves with this FN "program". The FN company, licensed by Colt, had a ready go 1050rpm gun in 1939 and yet it took the US until late 1944 to come up with a 1100-1200 rpm version? And I mean the US as three different companies (two in addition to Colt) were trying to get the guns to fire that fast at an acceptable to US military rate of jams and parts breakage. There were at least 15 different model numbers of prototype guns. Now the US did make things harder by insisting for several years that the "new guns" should be able to be make from old guns using a parts kit. They had to give up on that. What changes did FN make? or what was their jam/ malfunction, parts breakage rate per 1000 rounds? And somehow this FN development never made it back to Colt?
Barrel wear would be truly horrendous. US .50 cal guns got chrome lined bores and before the end of the war were getting stellite linings to keep the barrel were under control in 800rpm guns. Ammo is also dependent on propellent.

FN apparently developed a HE shell for the 13.2mm variant of the MG. Not sure how good such a thing is,

HE round:
Projectile weight: 42g
HE weight: 3.5g

20mm Hispano used a 128-130 gram projectile with about 10 grams of HE. So you need about three 13.2mm HE rounds to equal one 20mm HE round.

For some reason the Germans, Italians and Japanese tended to use multi function projectiles, like HE tracer which meant that the tracer compartment cut into the space available for the HE. OF course if you use a dedicated HE projectile you to have to mix in a certain percentage of tracer projectiles and/or a certain percentage of AP rounds. For example the famed German 20mm mine shell was only about 40% of the ammunition belts of the MG 151/20. The Mine shell could not use tracer so they had to have a certain percentage of tracer and certain percentage of AP ammo. The mine shells tended to detonate on the aircraft skin or very close to the skin after penetrating.
Hispano guns used mix loads too.

Now we come to the propellent problem. I have no idea what the FN guys were using for propellent. The Americans changed the Propellent in both the .30-06 cartridge in very late 1930s and in the .50 cal cartridge in 1939/40. They got better veleocity with lower pressures and less barrel wear (lower flame temperature). It took the British years to change the propellent in the .303 ammo. British manufactured .50 cal used the old propellent and the US manufactured ammo to British specs use the British velocity specs even if they used the new powder.
20mm powder was faster burning than US . 50 cal powder because the case had much less bottle neck.
FN might very well have gotten some of the new powder from the US for testing. The Ability to get tons per week might be a different story.

A lot of questions about the FN 13.2mm Browning gun. Swedish modifications and Swedish ammo supply show what might have done with more time (and with different ammo supply)

 

[tomo pauk]

The FN company, licensed by Colt, had a ready go 1050rpm gun in 1939 and yet it took the US until late 1944 to come up with a 1100-1200 rpm version? And I mean the US as three different companies (two in addition to Colt) were trying to get the guns to fire that fast at an acceptable to US military rate of jams and parts breakage. There were at least 15 different model numbers of prototype guns. Now the US did make things harder by insisting for several years that the "new guns" should be able to be make from old guns using a parts kit. They had to give up on that.

Perhaps FN was just better in sorting out the things in this case? They certainly were not giving a d@rn about what US ordnance was demanding from the US companies, either.

What changes did FN make? or what was their jam/ malfunction, parts breakage rate per 1000 rounds?

Perhaps A A.G. Williams can enlighten us.

And somehow this FN development never made it back to Colt?

Were they obliged to make feedback to Colt?

 

[z42]

Define "waffling about". The British had a signed license agreement in 1937 (?) and a factory under construction in 1938 and the first ceremonial production gun fired in Jan 1939.
Actual production took a bit longer but you can see the overlap on the FN gun.

So my hypothesis is that, if in the mid-30'ies they had decided to go for a HMG caliber gun, and for it be initially deployed it in existing fighters, they could have a HMG-equipped fighter force at the outbreak of hostilities, or at least significantly sooner than it took to deploy the Hispano. Another thing that I guess took extra time with the Hispano deployment was the initial attempts to deploy the drum fed version, which left a lot to be desired in many ways, and then the redesign work for the belt feed. OTOH it's unrealistic to expect that everything goes butter smooth, and what in retrospect might look like waffling about is just trying different things that turn out to not work very well.

Now the whole (or large part) of the 13.2mm ammo argument assumes the British (and Americans, they were suppling a fair quantity of the ammo to the British even in 1940) can supply the desired types and quantities of the 13.2mm ammo when they could not supply the existing .303 guns, the Vickers .5in guns and American .50 cal guns with high performance ammo (high performance means better than ball ammo)

AFAIU the FN HMG was offered in both 12.7x99 (.50 BMG) and 13.2x99/96 Hotchkiss, so if the UK would have thought commonality with the Americans important, they could have chosen the 12.7mm version. Though perhaps it's a tall order to foresee the level of cooperation between the UK and USA during WWII in the mid-30'ies when the caliber decision would have been made.

I would be a bit leery of enterer production, the British needs high hundreds or thousands of guns per month. Not one hundred per month. How many did FN actually make?

FN never had much opportunity to make them before Belgium was knocked out of the war. I would assume that whichever HMG was chosen, the Brits would require the design to be manufactured on British soil, precisely to guard against such eventualities.

 

[Glider]

I don't think that there was a huge difference between the 0.5 M2 being made fully effective and the 20mm. The 20mm was the better long term solution and any effort fixing the 0.5 would have lengthened the time taken needed on the 20mm. So in the long term I think they made the right choice.

 

[tomo pauk]

I don't think that there was a huge difference between the 0.5 M2 being made fully effective and the 20mm. The 20mm was the better long term solution and any effort fixing the 0.5 would have lengthened the time taken needed on the 20mm. So in the long term I think they made the right choice.

British can start with airborne .5 in in early 1930s, well before the Hispano is in the cards.
From here:
The Mark II entered service in 1933 and was mounted in some British light tanks.

 

[A.G. Williams]

A few points: the RAF were evaluating the .5 Vickers alongside the 20mm Oerlikon Type S about a decade before WW2. They decided that the 20mm was much superior as fighter armament, so went looking for the best 20mm cannon they could find. Unfortunately, they settled on the Hispano HS 404 which was only at the prototype stage in the mid-1930s. This was heavy (50 kg) but fairly fast-firing (700 rpm) and had a high MV (around 850-880 m/s). The contemporary Oerlikon in French service (HS Type 7 and 9, IIRC) was the same weight but only fired at 400 rpm and had a slightly lower MV (820 m/s), so the Hispano performed much better.

HOWEVER..... A more advanced version of the 20mm Oerlikon (the FFS) was developed in the mid-to-late 1930s which weighed only 39 kg and fired at 470 m/s. At the same time, the HS 404 was wound down to around 600 rpm in the interests of reliability. Suddenly, the relative advantage of the Hispano became a lot smaller, but by the time this was obvious, the British were totally committed to the Hispano.

As far as FN Brownings were concerned, I suspect that FN had better design engineers than the US (the US produced nothing remarkable in the way of aircraft guns until after WW2). FN revved up the .30 Browning to a phenomenal 1,900 rpm, although wound it back to 1,400 rpm in the interests of gun life. As far as 12.7mm vs 13.2mm is concerned, the difference was marginal. 12.7mm HE ammo was developed during WW2 in the USA, but not adopted - they preferred API.

As I have mentioned elsewhere, my choice of RAF aircraft guns in the run-up to WW2 would have been the 20mm Oerlikon FFL (smaller and lighter than the FFS) and if there was time, I would have commissioned FN to develop a smaller version of the .50 Browning to fire .5 inch Vickers ammo - that would have been great for turret armament.

 

[tomo pauk]

Thank you for the reply

HOWEVER..... A more advanced version of the 20mm Oerlikon (the FFS) was developed in the mid-to-late 1930s which weighed only 39 kg and fired at 470 m/s.

That would probably be 470 rd/min, not m/s?

 

[Shortround6]

we get into the what was available when problem.

One reason the UK passed on the .50 cal Browning in the early trials was that it didn't offer than much more than the .5in Vickers,
The US .50 offered heavier bullets, about 48-49 grams vs 37.6 grams but at about the same veleocity.
In fact Kynoch in 1928 was loading .50 cal ammo for the test using 52 gram bullets. The cost was the bigger cartridge case, the bigger gun, a lot more propellent ( about 70% more) and a lot more barrel wear. It hits harder but the time of flight isn't that different.

Now what was FN offering for ammo and when?

One website says that a lot of the late 1920s and early 30s 13.2 Hotchkiss ammo was loaded by Kynoch in Great Britain. It also says that the 13.2mm Hotchkiss suffered form poor barrel life.
The big Vickers "D" cartridge was also tested and was probably too much of a good thing. The huge case held about 33% more propellent powder than the US .50 cal and used a lighter bullet (43.0-44.7g)to get it's high veleocity.
The ammo the US .50 made it's reputation in WW II was with 46 g bullets and 2800fps (853m/s) and this required the new propellent.
It was this higher velocity that both increased the hitting power and shortened the time of flight.

If you don't have the new propellent in large quantities it doesn't work.
The 20mm Hispano used a little over twice what the .50 did for propellent but it didn't need the slower burning powder that the .50 needed.

Another problem with 12.7mm-13.2mm HE shells is that you need tiny fuses, lots and lots of them, throw in a 3rd "lots"

I would assume that whichever HMG was chosen, the Brits would require the design to be manufactured on British soil, precisely to guard against such eventualities.

And this requires the British to sign the deal before the deal for the Hispano is sighed (and may stop the British from ever getting Hispano guns with a license, Marc Birkigt, was not happy with the British and felt they could not be trusted after a British company reneged on a deal to build Hispano engines in England). Buy and build land before doing so for the Hispano factory, and get the guns and ammo into production in late 1939 or early 1940.

And we have never answered the question/s about the FN guns jam/stoppage/ breakage rates.
The US Brownings did ok in US tests, they were abysmal in service use in Britain in 1941. In cowl mounts with heat.

One reason the US gun designers didn't make much of note in WW II was that they were busy building killer unicorns.
The Ordnance engineers were fixed in very high velocity heavy machine guns, like 3500fpm(1060m/s.)
The idea was than such high veleocity would simplify gunnery by greatly reducing the amount of lead needed for deflection shots.
I say killer unicorns because most/all of them failed for foreseeable problems. Like excessive barrel wear, large heavy guns and low rates of fire, Broken parts.
Taking a 20mm case and necking it down to 12.7mm bullets will give you high veleocity, but you also need a 20mm sized gun, you need a 20mm sized feed system, the gun is going to recoil like a 20mm (or close) and you are going to suck up raw materials like a 20mm gun.
The Americans were working on quite a number of different guns/programs. The fast firing .50 cal may have been something of a fall back position at times.
I seem to remember that they also wanted it to fire 1000 rounds with only 5 jams a perhaps one broken part?
The Russians got fast firing 12.7mm guns to work but they were more accepting of broken parts and jams were were willing to junk the whole gun after just a few thousand rounds and several barrels.
I am not saying the US was right, I am saying that comparing one Browning design to another when we don't the performance characteristics (jam and failure rates) may not give us a good picture of what the different guns could actually do.

 

[Jabberwocky]

The RAF was casting about for alternatives to the .303 Browning in the 1937-1940 period. There were a range of weird and wonderful armaments considered for the Spitfire:

• Browning Mk II in both very high rate of fire (more than 1400 rpm) and ultra high velocity versions.
• Aerial version of the Hotchkiss M1929 in 13.2x99 Long. I don't have much information on this weapon, but it apparently had performance similar to the Japanese Type 93 naval machine gun (weight just under 22 kg, RoF about 450 rnds/minute, muzzle velocity about 795 m/sec)
• Madsen light machine gun in 6.5mm, 8mm, 11.35mm. Rof was meant to be anywhere from 1000 to 1400 rpm, installed weight about 1 kg per gun more than the standard .303
• Madsen cannon in 23mm. Weight about 53-55 kg, RoF of 360 to 420 rpm, muzzle velocity about 720m/sec. Belt fed, reportedly with 100 rounds per gun.
• Vickers 12.7mm
• Vickers 25.4mm. This was a bit of an oddball, seemingly based on a Vickers naval AA gun. Muzzle velocity of 910-920m/sec but RoF of only about 100 or 120 rpm, and fed by a 30 round drum. Plus it weighed just over 127 kg per gun. Seems like it might have made a good aerial anti-tank gun, with the right ammunition.
• Oerlikon FF 20mm
• COW 37mm cannon
• Vickers 37mm cannon
• American Armament Co 37mm cannon. I think this is the same cannon as on the P-39.
• Hispano 20mm cannon.
• Hispano 23mm. I think this was the HS 404 re-chambered for the same ammo as the 23mm Madsen. Installed weight was 89 kg per gun, and feed was a 60 round drum.

 

[wuzak]

The Whirlwind and Typhoon did happen, both armed with 4 x 20mm then came the Beaufighter and Mosquito. The Hurricane and Spitfire started to be fitted with 20mm cannon in 1940 and it was standard fitment on the Mk II Hurricane and Mk V Spitfire in 1941. In 1941 the USA and Germany were still using "pop gun" rifle calibre ammunition and the USA was still having issues with the 50 cal operation during high G manoeuvers in 1943. The RAF downed a lot of planes in the Battle of Britain with their pop guns. My thought is you have just watched a well known Youtube video.

The Whirlwind was the cannon armed fighter to F.37/35.

The Typhoon was designed around specification F.18/37, which called for 12 x 0.303" mgs. It was changed to 4 x 20mm cannon early in production.

The Beaufighter was an "interim" cannon fighter to fil in until the Whirlwind was ready.

 

[wuzak]

Wasn't aerial gunnery a concern in the lead up to WW2, and the early war years?

That is, it took a lot more bullets to get a hit.

Also, the E wing for the Spitfire didn't arrive until 1944, around the same time as an improved sighting system.

 

[A.G. Williams]

Thank you for the reply



That would probably be 470 rd/min, not m/s?

Sorry yes, you are right.

 

[A.G. Williams]

The RAF was casting about for alternatives to the .303 Browning in the 1937-1940 period. There were a range of weird and wonderful armaments considered for the Spitfire:

• Browning Mk II in both very high rate of fire (more than 1400 rpm) and ultra high velocity versions.
• Aerial version of the Hotchkiss M1929 in 13.2x99 Long. I don't have much information on this weapon, but it apparently had performance similar to the Japanese Type 93 naval machine gun (weight just under 22 kg, RoF about 450 rnds/minute, muzzle velocity about 795 m/sec)
• Madsen light machine gun in 6.5mm, 8mm, 11.35mm. Rof was meant to be anywhere from 1000 to 1400 rpm, installed weight about 1 kg per gun more than the standard .303
• Madsen cannon in 23mm. Weight about 53-55 kg, RoF of 360 to 420 rpm, muzzle velocity about 720m/sec. Belt fed, reportedly with 100 rounds per gun.
• Vickers 12.7mm
• Vickers 25.4mm. This was a bit of an oddball, seemingly based on a Vickers naval AA gun. Muzzle velocity of 910-920m/sec but RoF of only about 100 or 120 rpm, and fed by a 30 round drum. Plus it weighed just over 127 kg per gun. Seems like it might have made a good aerial anti-tank gun, with the right ammunition.
• Oerlikon FF 20mm
• COW 37mm cannon
• Vickers 37mm cannon
• American Armament Co 37mm cannon. I think this is the same cannon as on the P-39.
• Hispano 20mm cannon.
• Hispano 23mm. I think this was the HS 404 re-chambered for the same ammo as the 23mm Madsen. Installed weight was 89 kg per gun, and feed was a 60 round drum.

The RAF didn't get very far with improvements to the .303, except for the addition to the gun of open-bolt firing, which was successful in preventing the ammo blowing up through overheating. I think that the standard cordite propellant was more sensitive to that than the nitro powder used by other nations (the British had a long-term preference for cordite because its performance was more consistent in hot climates in places like Africa and India. However, by the end of WW2 they were changing over to nitro generally).

The 13.2 mm Hotchkiss was only made in land or naval mountings. It was unsuitable for aircraft case because the magazine and strip feeds contained only a few rounds, it was too slow-firing and too heavy. The Japanese Navy made the gun under licence for use as a light AA weapon under the designation 13 mm Type 93.

The 25.4 mm Vickers gun was a naval AA weapon only ever used in one ship (La Argentina) but it was considered as armament for the Spitfire. I agree with you that it would have been better as an airborne anti-tank gun.

I'm not sure which gun you mean by the "Vickers 37 mm". This calibre had been replaced by 40 mm in the Vickers line-up by the end of WW1, and they were never used in aircraft (except for the 40mm S Gun, of course).

The P-39's cannon had nothing to do with the American Armaments Corp (the AAC story is a saga in its own right). It was a Browning design.

The 23mm Hispano HS 406/407 was a bigger gun than the HS 404 because the ammunition was substantially larger and more powerful (also bigger than the 23 mm Madsen's). The French sold the project to the Soviets, who came up the 23mm VYa of similar performance a year later.

I am puzzled that the RAF seems to have taken no notice of the Oerlikon FFL in 20 x 101 mm RB, as used by Japanese fighters. This was only a few kg heavier than the .50 Browning, with a muzzle velocity which matched the .303 (handy for harmonising the weapons) and its initial rate of fire of 490 rpm was later increased to 620 rpm (and 720 rpm at the end of the war) with belt feed.

 

[Jabberwocky]

Hi Tony,

Thanks for all the information! Always nice to have speculation confirmed, or overturned.

Sources to hand (Morgan & Shacklady) only have the RAF considering the Oerlikon FF 20mm for the Spitfire, and then its seems to be only in passing. Supermarine even went to the trouble of a design study (Type 345) for a Spitfire armed with the 13.2mm Hotchkiss.

I'm sure the RAF were at least aware of the FFL. Chinn, in reference to the Oerlikon Aircraft Cannon, notes:

"England bought Oerlikon guns [FFg, FFL and FFS] as early as 1935 for testing at Enfield, ostensibly for antitank work, but in reality for adaptation to aviation use.

...
In this same year [1938] the British, running their second trials on the gun at Enfield, turned in a very favorable report on its ability to use deformed or poor quality ammunition. The Royal Navy, desperately in need of a reliable automatic cannon for antiaircraft use, hastily adopted the FFS for shipboard use and ordered 500,000 rounds of ammunition to be made up immediately. The development of high-explosive projectiles had long been proved successful and all orders carried a stipulation that these be made in proportionate numbers."

The guns were even being written up in the popular aviation press of the time:
file:///C:/Users/simon/Downloads/Armament%20of%20single%20seat%20fighters.pdf



Question outside of the topic area: Your website appears to be gone. Are you no longer hosting it, or did something else happen?

 

[z42]

Wasn't aerial gunnery a concern in the lead up to WW2, and the early war years?

That is, it took a lot more bullets to get a hit.

Yes, and the "shotgun" approach with lots of .303's was used as an argument why small caliber guns was better. The rather huge hole in that argument, of course, is that, statistically, "a hit" with .303's is very unlikely bring down a plane. While ultimately the autocannon side of the argument won, at least initially that side wasn't helped by the reliability and other issues with the initial Hispano installation.