WW2: why so many .303 guns?

[Ignition Override]

Hello: Just an off-the-wall question from a "colonial", who never tires of reading about/watching the amazing exploits of the RAF.

Why did so many, if not almost all British fighters/bombers in that war have guns with only .303 caliber guns, instead of the .50 as on many Yank planes? Was it mostly a matter of the weight of the ammo belts etc? Let's exclude the cannons on the stupendous Beaufighter etc.

What was the main caliber of the Luftwaffe guns?:8

[Daysleeper]

Cos the yanks were late as usual and therefore had more time to fit bigger guns...:O

Sorry.

.303 (7.62mm ish) was the standard British army rifle and machinegun round so I think that is why it was selected initially.
The standard fit for RAF single seat aircraft developed into 4 20mm cannon by the end of the battle of britain late 1940. This was based on the bitter experiance of german bombers wandering on despite being turned into sieves. It took some time to develop cannon for the wing mounts that were happy up to 30,000 feet and this was eventually solved with hot air feeds to prevent the breaches freezing.
So in fact they were more heavily armed than the Mustang (4 x 12.7mm) tho i suppose was really british as well.
It is debatable whether 4 x 20mm cannon firing an explosive shell was better than 8 x .5s(thunderbolt and others) firing non explosive shot.

Contempory german fighters, Bf109g (1943) had 1 30mm cannon in spinner and 2x 13mm machine guns. bf 110g (night fighter) 2x30mm 2x20mm rear gunner 2x7.9mm
This had evolved following experience starting in spain in 1936 when the 109 had just 2 x 7.9mm machineguns.

British bombers , Lanc 2 twin .303 and 1 quad .303,
American
B-17 9 x .5 (12.7mm)

The later british bombers designed for night use where the gunners were really more use as lookouts. Indeed there is some debate as to whether they would have been better leaving the guns and turrets behind entirely and getting better height , though Bomber command would probably have just put more bombs on.
The Americans had the knowlege of British use of the B-17 in daylight ops (disasterous) and decided to up gun it before they used it themselves.

So as you can see everyones ideas about aircraft armament developed through war experiance. Its just the Germans had a head start and the Americans gained a lot of British data.

[spekesoftly]

I would guess that one reason was because, for many many years, the .303 round was standard issue to the British Military. Adaptation for use on RAF aircraft probably brought cost, logistic and supply advantages. (The bean counters again!)

Cannons were susequently fitted to a lot of RAF WWII fighters/bombers, to increase their hitting power.

[Archimedes]

1. .303 was standard calibre; the calculations about weight of fire leading to the decision that 8 guns were needed were based around this, IIRC.

2. Once .303 was proven to be a bit lacking (late 1940), ISTR reading that the plan was for fighters to have 20mm, with bombers getting .5. After Pearl Harbor, the Americans needed all the .5 they could get, which substantially delayed fitting weapons of this calibre to RAF aircraft.

My memory may well be flawed on both accounts, apart from the fact that .303 was the standard calibre (and appeared adequate at the time the aircraft were designed).

[Army Mover]

I have a friend who was a FAA pilot during the war. I've just asked him if he has any memories to contribute. His first thought was he didn't have a clue, but he's now had a chance to think about it, he's offered the following. Initially it was down to weight, the .303 being an overall lighter system. He also recollects "There is also the obduracy of the politicians on cost.....", so things don't appear to have changed much. :*

[DC10RealMan]

Re the British bomber armament. Air Chief Marshal Harris, C in C Bomber Command was asked by an Air Gunner why they were not given .5 machine guns instead of .303. Harris replied "how far can you see at night on ops", "about 300 yards" was the reply. "Exactly" says Harris "Whats the point of having greater range if you can not see the target". I cannot fault his logic and it confirms that the gunners were more useful as lookouts than engaging night fighters armed with cannon and machine guns in a gunfight.

[Archimedes]

That's interesting. Harris's official comments on the lack of a .5-inch are a bit different. He was responsible for getting the FN 82,. B-P 'D' (.5-in) and B.17 (20mm) turrets onto the stocks (as it were), but development was so slow that he recorded:

"Throughout, those responsible for turret design and production displayed an extraordinary disregard of the requirements of the command"


I can't help wondering whether the case above mightn't have been the AOC-in-C giving one of his men a plausible reason for why heavier calibre weapons weren't available. Even at close range, the .303 was lacking in 'Oomph' as opposed to the .5, and I'm pretty certain that I've read somewhere (Bomber Offensive? The Official History?) that he knew this and wanted action to deal with it.

[DC10RealMan]

I was also aware of 0.5 machine gunned turrets, I may be wrong but I thought that this was a local modification on 5 Group aircraft based in and around Lincolnshire. The modified turret was called a "Rose turret" after the engineers Rose of Gainsborough who were the engineers responsible. The RCAF 6 Group based in Yorkshire did something similar with a local modification of a single belly mounted machine gun as they suspected the existence of night fighters equipped with upward firing armament, in fact they were quite correct as the Luftwaffe had two upward firing cannon called Schragen Musik.

[Pindi]

The 0.5" turret was actually known as the Rose/Rice turret.
Rice was (I think) AOC 1Group and he inspired the turret. Alf Rose
built it in Gainsborough.

[Deaf]

IIRC The lack of 50's had something to do with tests in ~1930 which resulted in the adoption of the Browning. The same tests showed no advantage of the 50 vs 303. This became doctrine and nobody really considered the a/c changes from fabric to metal skins with some armour.

When the problems with this approach became obvious in the late '30's there was worry about 50 proof armour so the decision was made to go straight for 20mm. Unfortunately the 20mm was not well developed and the prevvious applications were mostly engine mounted. This combined with general stress on engineering resouurces with rearmanent meant the development fell though the cracks until the need became critical. It didn't take too much time to fix the guns but a lot longer to arrange for 4x20 in the Spit wing.

The problem with the turreted 50's and 20mm was basically just the fact the turrets had to be redesigned, developed and debugged. This was a much bigger job and hence took longer.

After the war the pendulum went a bit far in bigger guns eg the 5 inch (4.5 ?/5.4?) recoiless automatic cannon. This chewed a lot of resources before it was realised the engine development wasn't going fast enough to deal with a weight of about a ton without ammo.

[steamchicken]

Those will have been the tests that led to the 8-gun interceptor concept - a Sqn Ldr whose name I forget calculated that in a modern engagement, no-one could be expected to track the target for more than seconds 2, and hence armament had to destroy HM Enemies within that time. He concluded that this required 8x 1000 rounds per minute machine guns. Brownings had just become available and fitted the bill.

They were originally either .3 or .5, but the British version was bored out to .303. No idea why, but the proposal that it was for commonality sounds sensible.

Since when are our decisions sensible?

[ORAC]

Armament of competing fighters (http://www.quarry.nildram.co.uk/BoB.htm). It would seem .50 calibre was considered and discarded in preference to 20mm.

As to why the guns were modified to use .303, the following is given as a reason:

"The combination of severe economic problems and vast quantities of standard .303" weapons and ammunition in store after the First World War militated against the adoption of any new calibre. The 1930s rearmament programme therefore saw such weapons as the American Browning aircraft machine gun and the Czech ZB30 (better known in its British incarnation as the Bren Gun) expensively redesigned to fire the rimmed cartridge....."

[Ignition Override]

Thanks very much! You guys have posted some really interesting and enlightening info.

When we go to England this June, we will have only about eight days to see the top two museums in London etc.

Back to aviation. I've heard very good things about the aviation exhibits-and that Duxford is not far east or northeast of London?

Quite true that the policy of isolationism here resulted in little "high-profile" assistance in 1940, when much more was badly needed. Too bad that pilots had to go over there via Canada.

[kilo52]

I. O.

Take the M11 Motorway from London and follow the signs to Stansted Airport. Duxford is on your left before you reach Stansted.

One point to bear in mind regarding the use of 303 calibre machine guns at the design stage of WW2 British aircraft is that 303 calibre was THE standard throughout the British Empire. That means not just the UK and the Dominions but India (including what is now Pakistan) Malaya & Burma, as well as the Colonies in Africa and the Middle East and those States under British protection elsewhere in the World. The introduction of a new calibre of weapon in peacetime had enormous implications throughout the entire Defence Establishment.

Incidentaly 20mm cannon were used by 19 Sqn during the Battle of Britain but were withdrawn due to teething problems with ammunition feed.

[Unwell_Raptor]

I have just slipped into my anorak....

The P47 and P51 had six x 0.5 cal, giving a much heavier weight of metal in a burst than eight x 0.303.

The B17G certainly had 10 x 0.5 (2 chin, 2 upper, 2 ball, 2 waist, 2 rear). Some had cheek guns as well.

The awesome B25J(?) solid nose version had, I seem to recall, ten forward facing, two mid-upper and two rear 0.50. It must have rattled a bit when they fired them.

Early Spitfire cannon jammed through ingestion of dirt through the muzzles - thee solution was standard-issue condoms, rubber, aircraftmen for the use of.

[Archimedes]

Unwell Raptor -

ISTT that most P-47s had eight .5 inch (although two guns were sometimes removed to save weight).

B-25 had up to 12 forward-firing (eight in solid nose plus four in packs on the side of the fuselage) in addition to the mid-upper, although some of the aircraft had only two pack guns and some had none at all. The nose could be retrofitted to earlier models, and I gather (but have seen no evidence to support) that some B-25Ds were so modified.

As well as the dirt problem with cannon, they were initially mounted on their sides. Oddly enough, this led to jams.... The eventual solution was to mount them the right way up and compromise the elegance of the Spit's wing by putting bulges on upper and lower wing surfaces.

[Ignition Override]

Kilo45-thanks for the directions.

As for mm vs inches, isn't a .30 caliber bullet the same width as the 7.62 mm? A 20mm shell must have been just over an inch in diameter? Unrelated, but one show on the Discovery Wings Channel features the Soviet "Frogfoot" SU-25, which flew in the 80's. A short video showed a small cannon (23mm?) firing straight into the metal below the cockpit canopy, with the pieces flying out like a dirt clod, but no apparent penetration through the metal.

Back to WW2-did the Spitfire, Hurricane etc .303 ever fire any incendiary rounds? Or did any normal bullets have magnesium tips, as with some US fighters such as the P-47, in order to better show where the impacts were?

[Unwell_Raptor]

I just did a quick Google, and the American Air Museum says that the P47 had six or eight guns. So we are both right.

It weighed seven tons!

[henry crun]

UR, It was a big aircraft.
A long time ago I knew a guy who flew them during the war.

He said if things got too hot in combat his evasive action was to undo the straps and hide in the map case. :)

[MadsDad]

Kilo52, sorry but correction.

Duxford is after Stansted going from London on M11. Follow signs to Stansted then keep going a couple more junctions.

(Basically take M11 from wherever to Junction 10, (Stansted is J8)).

[Blacksheep]

Ignition Override,

The 7.62mm bullet is exactly 0.30 inches in diameter as are the American .30-30, .308 and the British .303 bullets. The second and third digits of the latter two calibers serve to indicate the size of the lands in the barrel of the weapons that fire them - an even number of .004" in the former and an odd number of .003" in the latter. The current 7.62 mm NATO is in fact exactly the same round as .308 Winchester.

A 20mm cannon shell is somewhat less than one inch as there are 25.4mm to the inch.

A .50 calibre bullet is not only thicker but also one third longer than a .303/.308 giving it 3.7 times the mass of the smaller bullet.

Moving up to 20mm cannon takes the projectile mass up to five times that of the .50 bullet and almost eighteen times the mass of the .303 bullet. It is easy to see why the larger calibre weapons were preferred by the fighter piots and air gunners. Typical engagement ranges were no more than 150 yards in most cases, its the weight of fire that counts rather than the ballistics.

The best indicator of hits is the bits of metal flying off the enemy aircraft...

...and size really does matter!!

[Sloppy Link]

Blacksheep,

You are obviously a highly technical individual, a couple of questions,

1. Lands....are these the raised portions of the rifling (ie the opposite of the groove)? There appears to be no indication of the amount of grooves or is six accepted as the standard?

2. Why is rifling appear by convention to impart a right hand spin although I do believe that some Chinese and Polish weaponds have a left hand spin but these are very much a rareity.

[Daysleeper]

"Don't worry lads at this distance they couldn't hit an elephaaargh"

[Danza]

One for the techies, lots of information here, I haven't had time to read it all ....

http://www.geocities.com/CapeCanaveral/Hangar/8217/fgun/fgun-pe.html


Ignition Overide, here is some other info from the web, so yes, the Spits and Hurricanes did fire other rounds than just standard ball rounds ....

"The B. Mk VI 'De Wilde' incendiary (named after the original Belgian inventor but in fact completely redesigned by Major Dixon), which contained 0.5 grams of SR 365 (a composition including barium nitrate which ignited on impact with the target).
The 'De Wilde' bullets were first issued in June 1940 and tested operationally in the air battles over Dunkirk. Their improved effectiveness, coupled with the fact that the flash on impact indicated that the shooting was on target, was much appreciated by the fighter pilots. It was at first in short supply, and the initial RAF fighter loading was three guns loaded with ball, two with AP, two with Mk IV incendiary tracer and one with Mk VI incendiary. Another source for the Battle of Britain armament gives four guns with ball, two with AP and two with incendiaries (presumably Mk VI) with four of the last 25 rounds being tracer (presumably Mk IV incendiary/tracer) to tell the pilot he was running out of ammunition. It is not clear why ball was used at all; presumably there was a shortage of the more effective loadings. (By 1942 the standard loading for fixed .303s was half loaded with AP and half with incendiary.)"

:)