.50 cal machine guns vs 20 mm autocannons on US aircraft

[DogFather]

P-51 had 6 x .50 caliber BMG (Browning machine guns)

P-40 had 6 x .50 cal BMG

P-47 had 8x .50 cal BMG

F4F Wildcat Guns: 4 × .50 cal BMG

F6F Hellcat either 6× 0.50 cal BMG, or 2 × 20 mm and 4x .50 Cal BMG

F4U Corsair 6 × 0.50 cal BMG, or 4 × 20 mm autocannons

Above are some of the most common US planes used in WW2. Looks like they tended to have more
.50 cal BMG, than 20 mm cannons. While, many Axis aircraft had 20 mm cannons. Besides the Axis
goal of shooting down bombers, why did German and Japanese planes tend to have 20 mm cannons?

I realize our fighters were designed to help protect bombers, so they were just shooting down fighters.
Seems like a enemy armed plane with 20 mm cannons, would have better range, and could hit a US
plane, before the US plane could fire. The 20 mm had less ammo capacity, that is I'm sure a factor.

I would think a fighter pilot would like to have both if possible, so he could take a longer range shot
if he got the chance.

What were some of the other pros and cons, of these two different weapons?

 

[davebender]

20mm cannon are far superior to .50cal MG if both weapons are equally reliable. The U.S. did not produce a reliable 20mm cannon during WWII so .50cal MGs were the only realistic choice.

 

[pbfoot]

http://www.ww2aircraft.net/forum/av...worst-specs-comparison-lmg-hmg-etc-29624.html

 

[vanir]

Some comments on this by Sqn Ldr Ralph Sorley, FO1 of the Air Ministry in evaluation of fighter armament proposals for service use new British monoplane fighters (Spit and Hurri) in 1934.
(paraphrasing for space and clarity) "The choice lay between the .303 gun, the 0.50 gun and a new 20mm Hispano cannon. Of the .303 guns the result was the Browning from American Colt company appeared to offer the best possibilities. Given the numbers of stockpiled Vickers, the acceptance of a new gun in the numbers required was a heavy financial and manufacturing commitment. During 1934 the Hispano gun is experimental and confirmed details about its performance are hard to establish. The 0.50 on the other had had been developed little (in 1934) and although it possessed better hitting power it was a slow firing and heavy item together with its ammunition. A trial on the ground of eight .303 guns was sufficiently convincing and satisfying to carry the day."

Just thought it might put the time where this decision was made in Europe into perspective. Seems the Japanese and Germans were more than happy to test experimental technologies in front line squadrons, it paid off as it turned out. The Americans were happy to go with a "little tested" gun, but first fitments were always alongside 0.30 brownings as they were a known quantity in terms of serviceability in the field. First 1x fifty and 1x thirty went on some American fighters, then 1x fifty and 3x thirty, finally 2x fifty and 4x thirty in the Hawks. I think the retention of the thirties here extrapolates the reasoning, but once it was well tested and found reliable, you had just 2 to 8 fifties in American fighters from then on.

The Oldsmobile 37mm was the all American aero cannon but it was unreliable and low performance, the Hispano was licensed produced as an alternative. Tony Williams schooled me on it once but I can't remember everything so he's the best source for more on that. The Hispano underwent progressive refinement, it had a few faults originally. So it makes good sense why the fifty was the main American gun.

 

[vanir]

Actually you know what Dogfather, the kind of thinking track you're on here I recognise and I think you might be much better served by dropping allied planes for a moment and think of german planes and armament instead.
They combined light and heavy MG with cannon. They also made it an artform like how you're suggesting. For the Ta-152C-3 final armament proposal for example MG151 were selected in 15mm calibre (which had previously been vastly downgraded in production due to rechambering for 20mm), specifically because the ballistics matched extremely well with the experimental MK103m motorgun that was to be fitted.

One of the issues mentioned in litature for later Me-109G is the disparity of ballistics between the MG131 and MK108, so much so that it causes two vertical convergence ranges at about 150m in front of the plane and again at about 400m if the armourers have sighted it properly, so those were your two best deadly ranges.
Something like an MG151 and MK103 combination however you get uniform convergence from about 75m all the way to about 800m in front of the plane, with very flat trajectories and good qualities.

This sound like the sort of thing you had in mind?

 

[Shortround6]

20mm canon were all over the map as far as muzzle velocity and "effective" range went, muzzle velocities ranged from 550 to 880 meters per second. With WW II range finders (often MK I eyeball) and guns sights long range cannon shots were more wishful thinking than practical reality.

US .50 cal also had 3 rates of fire depending on which year. 600rpm (or under) during the 30s and sometime into 1940. 800-850 rpm from some point in 1940 ( for new guns or could older ones be modified?) and finally 100-1200rpm in the spring/summer of 1945 (definitely new guns). These rates of fire were for free firing guns. Synchronized guns were slower, sometimes a slow as 450rpm.

 

[Shortround6]

20mm canon were all over the map as far as muzzle velocity and "effective" range went, muzzle velocities ranged from 550 to 880 meters per second. With WW II range finders (often MK I eyeball) and guns sights long range cannon shots were more wishful thinking than practical reality.

US .50 cal also had 3 rates of fire depending on which year. 600rpm (or under) during the 30s and sometime into 1940. 800-850 rpm from some point in 1940 ( for new guns or could older ones be modified?) and finally 100-1200rpm in the spring/summer of 1945 (definitely new guns). These rates of fire were for free firing guns. Synchronized guns were slower, sometimes a slow as 450rpm.

 

[GregP]

You should not be asking about German guns as suggested above unless you are interested. Your question was a good one without regard to nationality. There are great websites with fighter gun effictiveness ratings in them, to include damage and power. Energy is power times time.

The Browning M2 basically fires at about 800 rounds per minute and delivered a 1-second energy burst rating of 368 or 491, depending on whether you had 6 or 8 fifties. The Me 109 G had a single MG 151 / 20 and two MG 131 MG. In a 1 second burst, they delivered a 1-second energy burst rating of 296.

The cannon was slightly slower at 750 RPM and the MG were slightly faster at 900 rpm, but were very low in power (3.2 compared with 4.6 for the Browning).

So, the six fifties delivered about 1/6 more energy in a 1-second burst and the eight fifties delivered about 40% more energy in a 1-second burst, compared with the Me 109 if both were fring ball ammo. All in all, it was about a wash ... if the target happened to be at the convergence point of the wing-mounted fifties. If not, I'd opt for the fuselage-mounted guns over the wing-mounted guns anytime. The high-ranking German aces used to say, one in the fuselage is worth two in the wings anytime.

If the 20mm were firing HE, then more energy was delivered, but at a slower rate. So, fewer hits were scored and the advantage was a bit lost due to short target tracking time.

So, about a wash ... for the Me 109 versus the 6 or eight fifties. If the 109 had the underwing cannon gondolas, it was better (energy-wise), but was also slower and less maneuverable due to drag and weight. I'd take the Mustang any day, but that is a personal choice. Once you get into the 30 mm and larger armament, the cyclic rate of fire is so low that the chances of a hit against a maneuvering fighter are very low ... but, if you GET one, the hit is devastating.

I'd say you can count on delivering a total of about 0.1 seconds of hits against a maneuvering fighter. The faster rate of fire is important, especially in WWII, moreso than the caliber ... unless there is HE involved. If so, then the damage potential is higher, commensurate with lower rate of fire.

The subject is a good one, worth investigation. Several authors cover it pretty well. Tony Williams' website (Google Fighter Gun Effectiveness) covers it pretty well and he is very knowledgeable about it. I wish the US had switched to 20 mm cannons earlier, but we needed a good weapon to switch to before that would have been advisable.

The early F-86's had six fifties, too. Later, when we HAD a good 20 mm, the F-86 swiitched to four 20 mm cannons. After that, the 20 mm cannon was the basic US fighter gun, with 30 mm being sought when necessary. Most other nations also did that switch on their own, some even in WWII, before we did, or followed when the logic became apparent.

The German weapon selection was good, but not demonstrably better as a whole in WWII. Likewise, the Japanese also had some cannons and MG mixed. They were good, too, but not demonstrably better in WWII.

Later, almost EVERYONE went to a 20 - 37 mm cannon in the gun configuration for fighters. The MiG-15 in Korea had two 23 mm cannons and one 37mm cannon. They hit very hard if they hit. The Sabres had six fifties and won the conflict easily with a good kill ratio. It was due to pilots, not to the gun selection or to the aircraft. The MiG-15 was and IS a good plane. It has weaknesses, as does the Sabre, but is about equivalent to the Sabre ... except for the fact that Sabre pilots wore g-suits; THAT made a large difference ... they stayed awake longer in a high-g turn!

But that is another subject and I don't want to hijack the thread about it ...

 

[Jabberwocky]

The German weapon selection was good, but not demonstrably better as a whole in WWII. Likewise, the Japanese also had some cannons and MG mixed. Theywere good, too, but notdemonstrably better in WWII.

I'd argue that German air to air weapon selection WAS demonstrably better than the US selection, which was essentially forced upon the USAAF/USN as US projects for better aerial weapons (US version of the Hispano 20mm, .60 T17E1/E3, T18, M10 37 mm ect) kept failing to produce a wholly workable product and it had to fall back on the .50 Browning.

In terms of firepower vs weight, an MG151/20 was around 2 times more efficient than a .50 Browning, a MK 103 around 2.5 times and a MK 108 about 5 times.

The fact that in terms of damage potential, the FW190A-4 could haul around 30-40% more firepower than a P-47 (depending on exactly how you measure it), for almost 50% less weight speaks volumes to me.

Time in seconds, needed to fire the equivalent of an ammunition power of 2320 (4 x MK 103 for 1 second) and armament weight, ammunition included (from Tony William's data)

P-39D: 7.2 sec for 367 kg of armament
P-40C: 14.2 sec for 230 kg
P-40E: 6.5 sec for 332 kg
P-51D: 6.5 sec for 385 kg
P-38: 5.8 for 419 kg
P-47: 4.8 for 613 kg

Bf-109E: 8.1 sec for 149 kg
Bf-109F4: 10.3 for 129 kg
Bf-109G6/R6: 3.3 for 286 kg (Twice the firepower of a P-40E for 15% less weight)
FW 190 A4: 3.5 for 310 kg (1/3rd more firepower than a P-47 for just over half the weight)
FW 190 A8: 2.8 for 431 kg

 

[tomo pauk]

Think that this wraps it up.

 

[gjs238]

Interesting Wiki article
Hispano-Suiza HS.404 - Wikipedia, the free encyclopedia

I would love to hear more about experiences with the single 20mm in the P-38.

 

[tomo pauk]

FWIW, it's pretty hard to find out any bad words about that plane/cannon combo. Ditto for about same gun in P-400 (P-39 with drum-fed Hispano of British origin).

 

[davebender]

Not completely. Fuselage mounted weapons are probably worth two wing mounted weapons as dispersion and wing flexing are not an issue.

Except for the twin engine P-38 you cannot mount enough .50 cal MGs in the nose to get the job done so you are stuck with wing mounted weapons.

A single Mg151/20 or Hs.404 cannon is powerful enough to knock down fighter aircraft and it can be fired through the prop hub. A single 3cm Mk108 cannon will knock down any aircraft and it will also fire through the prop hub. The powerful cannon and a hollow prop shaft work together to produce the best possible WWII weapons solution. Germany and France figured this out during the 1930s. Not sure why Britain didn't go this route with the RR Merlin engine. For the USA it's a moot point as we couldn't even produce a reliable aircraft cannon.

 

[tomo pauk]

It's far more up to the engine, than up to the gun, whether the gun could be fired through the prop. No magic will make Mk-108 to fire through a prop of an engine is not allowing so. You can also see MiG-1/3 Il-2/10 - Mikulin engine was the obstacle to mount the moteur-cannon.

For USA, it's not a moot point at all.
Let's consider USAAC fields an Allison V-1710 allowing for such a cannon. The plane features one cannon + 2 cowl HMGs, without all the P-39 hocus-pocus. Such a plane can use 20mm that P-38 got (some 9000?), until then using the 37mm. Hull mounted gun is less prone to malfunction, there is less guns to build mantain, the armament weights less than 6 HMGs (for same destructive power) and about as 4 HMGs (but has better destructive power).

The way I see it, choice of both engines and guns/cannons available for UK USA fighters was ill suited for the armament installed to excel in punch-to-weight category - engines not allowing for a cannon to fire through prop, while Hispano was unsuited for synchronization.

 

[Edgar Brooks]

. Not sure why Britain didn't go this route with the RR Merlin engine.

There isn't enough space in the "V" between the cylinder banks, to allow the cannon so sit within the confines of the engine. It would have to perch on top, which would have lengthened the front gear box, which would have necessitated a deeper nose, which would have made the aircraft more slab-sided, which would have made them less aerodynamic. It wouldn't have helped the CofG, either; wing-mounted guns can have their breeches/ammunition boxes set on the CofG, so using up the ammunition makes virtually no difference to the trim.
Anway, this thread is not interested in British aircraft; my apologies for butting in.

 

[Tante Ju]

There isn't enough space in the "V" between the cylinder banks, to allow the cannon so sit within the confines of the engine. It would have to perch on top, which would have lengthened the front gear box, which would have necessitated a deeper nose, which would have made the aircraft more slab-sided, which would have made them less aerodynamic. It wouldn't have helped the CofG, either; wing-mounted guns can have their breeches/ammunition boxes set on the CofG, so using up the ammunition makes virtually no difference to the trim.
Anway, this thread is not interested in British aircraft; my apologies for butting in.

I think reason is because supercharger is placed in position making installation impossible on RR. But Hispano Suiza (and Russian copy) could fit cannon between cylinder bank.

 

[Denniss]

I don't think any engine had the cannon between its cylinder banks, they just had to have enough space for the gun barrel with the main gun componentes fitted behind the engine.

 

[vanir]

Denis it's a shortening of the nomenclature "firing between the cylinder banks" which is perfectly colloquial. You don't really "fly a plane" either, an aerofoil is planing through atmospheric relative density and you try to influence its motion, forget that and you turn into a rock but everyone says "fly the plane". How, big breath and blow at it?

GregP, I believed you missed my point entirely mate. The reason I brought up German armament conventions was purely because nobody else actually thought about complentary ballistics qualities with combined armaments (cannon, mg), except the Germans, which even they didn't really until 42 and didn't implement a translation into production until war's end. But at least they were thinking about it, as the Rechlin armaments testing records show, most especially for newer schlacht role attack-fighters which are meant to carry a combination of guns, MG and cannon is very typical (eg. zerstörer armament, in the lehr-staffeln these pioneered the schlacht and schnellbomber doctrinal shifts of 43). They were thinking about which MG and light Cannon combine particularly well for light-anti-armour work, the star of the show being the MG-151 in 15mm original chambering, with the MK103 using penetrator warheads (not tungsten).

Since discussing complementary ballistics in combined armament fits was the OP, it was a natural relation. The US didn't approach aero armament, or fighter performance for that matter, anything like the Germans did. Neither did the Japanese, nor anybody else although the British Air Ministry comes close, but no closer than TsAGI. Germans took to aero armament exactly like a bunch of armourers from the artillery corps.
But let's say we dispute that. Who cares? The point is a detailed record which cannot be found for any other service, clearing comparing and group matching ballistics qualities of the all the different aero guns, distributed to geschwader (handbuch der flugzeug bordwaffenmunition), and updated. I'm OKdLeN, my orders are kill the bombers, look up in the book, oh we need JG11 over here, they've got MK108.

Americans are like union bosses, talk good but Germans are like machinists, underpaid. When I want something done I'll call the machinist.

 

[renrich]

The AAF liked the 50BMG because it allowed for 6-8 guns with a lot of ammo which enabled the pilot with not great gunnery skills more opportunity to get hits. The USN came around to the point of view that the 20 MM cannon would make a better armament package. Perhaps their POV was influenced by possibly more emphasis on gunnery skills in USN pilot training. Just my guess. The AAF's and USN's opinions were stated in the "Report of the Joint Fighter Conference, 1944."

 

[tomo pauk]

The AAF/USN did have something that other AFs lacked, and they lacked something other countries had.
The assets were engines of high power reliability, available in good numbers. Such engines (and we move now to what they lacked) have had no objections to haul a hefty battery of guns, guns lacking in power-vs.-weight ratio (along with plenty of ammo for numerous guns). Another thing is that, for all USAAC/USN fighters that mattered, a centraly mounted battery was at least ineficient, not to say impossible to install. A P-51 with 3 Shvak cannons, or a P-47 with 4 would posessed a better destructive force, for lower weight drag penalty and withouth reducing ammo count.

The report is from 1944 - the year that Wildcat reverted to 4 HMGs in the FM-2 variant?
With engines of 1100-1200 HP (a better part of war) the US planes have problem - if they want an effective battery, they need 6 HMGs, but that's quite a weight penalty, even a bigger one when we include a hefty load of ammo. If we reduce the ammo count, that's bad (F4F-4 issue). If we want to go light, we field 4 HMGs, and that's not efficient.
Perhaps it's better to have 2-3 cannons, to save weight have good destructive power? Alas, the cannons US could get can't be synchronised, so they must go out of prop disc (two cannons in wings - with one malfunctioned, plane is as good as unarmed).

So I'd say pilots praised what they had, and they had only the fifties.