Guns vs cannons

[sturmkraehe]

A very American-style documentary (I am not judging, only describing a certain style) on the 109 vs Spit debate. I post this video clip because at about 11' it gets interesting as they test a Browning 303 vs a 20mm cannon on an aluminium sheet. 

 

http://www.youtube.com/watch?v=BpTrygZfC-g

 

 

[IonicRipper]

I thought what made cannon shells more destructive were the explosive charges in them? Not the hole size they made...

[Sternjaeger]

yeah, that's more for show than for anything factual really... the hole size might matter in term of physical destruction (making big holes on spars will weaken the structure), but this test doesn't take into account explosive rounds nor the very high rate of fire of the brownings used on spits (and for the record, neither of the two guns testes were actually the exact ones mounted on Spits or Me109s).

[MarcoRossolini]

Don't forget also the (IIRC) rather low muzzle velocity of the 20mm cannon, as well as the fact that the more numerous hurricane could take more punishment due to its hybrid construction...

[Emgy]

Btw it's funny they show what looks like a towed 37-47??mm AT-gun, saying "shoehorned into the tiny Messer's wings was this..."

Edited February 20, 2014 by Calvamos

[Finkeren]

Don't forget also the (IIRC) rather low muzzle velocity of the 20mm cannon, as well as the fact that the more numerous hurricane could take more punishment due to its hybrid construction...

 

The low muzzle velocity and rate of fire was only really an issue with the MG FF. The MG 151/20 was a different story.

[Skoshi_Tiger]

The low muzzle velocity and rate of fire was only really an issue with the MG FF. The MG 151/20 was a different story.

The Hispano cannon had a muzzle velocity of around ~2800fps, compared with the colt-browning .303 that had a MV of ~2450. So in fact the Hispano's were flatter shooting than the Browning .303 MG's

[Sternjaeger]

The Hispano cannon had a muzzle velocity of around ~2800fps, compared with the colt-browning .303 that had a MV of ~2450. So in fact the Hispano's were flatter shooting than the Browning .303 MG's

 

well, a faster at muzzle speed would only give you a flatter trajectory if we were talking about the same kind of bullet. The HS 20x110 round is considerably bigger and heavier than the .303. I don't have any figures handy but it wouldn't surprise me if ballistically the .303 was superior, despite the HS faster muzzle speed.

 

Muzzle speeds are often deceiving and not good for comparison, especially among different calibres.

Edited February 24, 2014 by Sternjaeger

[VO101_MMaister]

well, a faster at muzzle speed would only give you a flatter trajectory if we were talking about the same kind of bullet. The HS 20x110 round is considerably bigger and heavier than the .303. I don't have any figures handy but it wouldn't surprise me if ballistically the .303 was superior, despite the HS faster muzzle speed.

 

Muzzle speeds are often deceiving and not good for comparison, especially among different calibres.

 

Mr. Newton would certainly disagree with you now.

 

 

Where the weight matters is the kinetic energy of the bullet. Heavier ammo with the same speed has more of it.

Edited February 24, 2014 by VO101VO101_MMaister

[Sternjaeger]

It's all proportional to the mass you have to move: you will need a lot more energy to move a heavy 20mm round, compared to a .303, and even if the faster muzzle speed will mean that initially the 20mm will leave the barrel faster, you'll see that it'll bleed its  energy faster as well, because gravity and friction will affect its trajectory quicker than the .303.

Edited February 24, 2014 by Sternjaeger

[79_vRAF_Friendly_flyer]

They projectiles are already "moved" when when they leave the barrel, so the only way they bleed energy is through air resistance. The air resistance again is depended on the weight to surface ratio. The .303 is lead and copper throughout, so it is cubic for cubic heavier. The 20 mm is larger however, and the larger the object the greater the volume is to surface. Without knowing the specific air resistance property of both, it is impossible to see who will drop faster, but from just guestimating, I'd put my money on the Hispano projectile as having the best (i.e. flattest) trajectory.

[Sternjaeger]

not to mention that the guns are actually installed at a certain angle from the wing chord... 

[GOAT-ACEOFACES]

Why did the USA stick with .50cals while everyone else was developing several versions of 20mm and 30mm?

 

Simple the USA was not faced with the need to stop raids by heavy, well-protected bombers. The destruction of American heavy bombers was a strong incentive for the axis to development of weapons of larger caliber. In Western Europe the main adversaries of the USAAF were fighters, which were much easier to damage and shoot down than bombers. In the Pacific Theatre the Japanese aircraft were initially poorly protected and easy to shoot down. Later Japanese aircraft were better protected, but again these were usually fighters.

 

So where the Americans right to rely on the .50 M2 when all other combatant nations had a clear preference for cannon of at least 20 mm caliber? The answer is YES! The M2 was adequate for its purpose, and was the only satisfactory aircraft gun in production in the USA. It was very reliable, was made in huge quantities, and the simplification of supply by comparison with the diversity of weapons used by the Axis powers gave a major logistical advantage. The importance of logistics is typically lost on gamers, even though the USA was about the only country in WWII that had the logistics in place to deal with 20 different types of weapons, they were savvy enough to stick with it. That and the USAAF and USN was clearly, as Charley Sean would say "WINNING" thus the old adage of "If it ain't broke don't fix it" comes to mind.

 

In the end, if the Americans had faced the need to stop raids by heavy, well-protected bombers, they would have, and were one of the few countries that could have switched to cannons in a short period of time, much like the USN considered doing near the end of the war to deal wit the kamikazes.

Edited February 24, 2014 by ACEOFACES

[Finkeren]

It's all proportional to the mass you have to move: you will need a lot more energy to move a heavy 20mm round, compared to a .303,

 

Yes and that extra energy is supplied by the larger charge of propellant during the rounds trip down the barrel. Once it leaves the barrel, the projectile is at maximum kinetic energy. From there gravity and drag are the only two factors in play. But: The fact that it takes more energy to get a heavy projectile moving also means, that it takes the exact same extra amount of energy to slow it down again (conservation of energy, as per Newton and the laws of thermodynamics)

 

 

and even if the faster muzzle speed will mean that initially the 20mm will leave the barrel faster, you'll see that it'll bleed its  energy faster as well, because gravity and friction will affect its trajectory quicker than the .303.

 

 

Gravitational acceleration (which is what gives a projectile its roughly parabolic path) is completely, 100% independent of the mass of the projectile. It's wrong when VO101VO101_MMaister says that Newton would disagree with you, it's actually Galilei (a hundred years further back in time from Newton) The rate of acceleration is a constant, and only the drag can vary in this equation. Therefore gravity cannot affect a heavy projectile "quicker" than a lighter one.

 

It's also wrong when you say, that a heavier projectile will bleed energy faster than a lighter one, in most cases, it's actually the other way around. If you double the outer dimentions of a projectile, but otherwise keep its structure the same, you increase its volume (and therefore its mass) by a factor of eight, meaning that if the muzzle velocity is the same for the two projectiles, the heavy one will carry 8 times the kinetic energy of the lighter one. The amount of drag is a function of the shape and size of the projectile, and since the outer dimentions have only doubled, the drag doesn't increase by anywhere near 800% for the larger projectile, which will therefore bleed its energy slower than the lighter one.

Edited February 24, 2014 by Finkeren

[Finkeren]

well, a faster at muzzle speed would only give you a flatter trajectory if we were talking about the same kind of bullet. The HS 20x110 round is considerably bigger and heavier than the .303. I don't have any figures handy but it wouldn't surprise me if ballistically the .303 was superior, despite the HS faster muzzle speed.

 

Actually I just looked up the figures. The H.S. 404 is listed with a maximum effective firing range of 7,000yd, while range for the Browning is listed as only 1,500yd, so reality is exactly the opposite of what you think, and for the reasons I just listed above. 

Edited February 24, 2014 by Finkeren

[Sternjaeger]

mmmmh we'd need to crunch some maths here. Just out of curiosity, where did you get that 7000 yd range for the HS? It's a bit on the generous side if you ask me... 

 

And yes, I should have made myself more clear, gravity will affect both rounds in the same way, the differential factors would be the propelling force and the friction. 

[79_vRAF_Friendly_flyer]

The rationale Finkern wrote above is probably also why the .50 Browning has better ballistic properties that rifle sized calibres like the .303 British.

[Sternjaeger]

true, again the only way to ascertain this accurately would be by using the data I mentioned. Another thing to keep into account is that HS rounds were of different kinds, with varying profiles and weights according to the kind of projectile (HE were less aerodynamic, AP were heavier), which meant that there was a different dispersion as the range increased. 

[Finkeren]

mmmmh we'd need to crunch some maths here. Just out of curiosity, where did you get that 7000 yd range for the HS? It's a bit on the generous side if you ask me... 

 

 

Both numbers are just pulled from Wikipedia (yeah I know) You can propably find some more accurate sources, but I was just trying to show the general point, and I'd wager, that regardless of the source, the effective range for the autocannon will be greater than the .30cal MG.

 

The 7,000yd is most likely for the AAA version in a rigid mount. Mounted on aircraft, there are so many other factors limiting the effective range, that the ballistics of the gun and ammunition is more or less irrelevant.

[Sternjaeger]

yeah, I agree, but put an HMG like the 50 cal or the UB and we'd see better performance me thinks.. 

[Kurfurst]

7000 yards range for a 20 mm cannon is like the 2000 m range scale on old Mosin rifles - sure the projectile will perhaps that far, but you ain't hitting a house block at that range.

 

As far as muzzle velocity, its nice to have but at the typical 2-300 meter practical firing range, it just won't make much difference. Spread on higher powered automatic weapons is practically always larger due the flexing of the long barrel, and as far as damage goes - HE cannon rounds will rely on the amount of explosive filler for that. Kintetic energy will make no difference there (there is far more power stored in the explosive filling than the propellant, and the round will blast to small pieces when it hits target). Not to mention even lowest kinetic power 20 mm round was a massive overkill for light aircraft structures.

[Finkeren]

7000 yards range for a 20 mm cannon is like the 2000 m range scale on old Mosin rifles - sure the projectile will perhaps that far, but you ain't hitting a house block at that range.

 

Agreed. This is solely about the ballistic capabilities of the different calibers, which will rarely come into play IRL, especially when firing from an airborne platform. Even modern weapon systems has trouble giving precise cannon fire from an aircraft at ranges beyond 1 km. During WW2 shooting distances were in most cases so short, that ballistic trajectories hardly played any role at all.

[Bladderburst]

MGFF were not very good, not at all like the MG151. I have red of a spitfire pilot who got shot by a 20mm shell in the foot during BOB and the shell just squashed on the tip of his boot. So when people say that the spitfire was better armed than the ME109E it's true. 

[79_vRAF_Friendly_flyer]

MGFF were not very good, not at all like the MG151. I have red of a spitfire pilot who got shot by a 20mm shell in the foot during BOB and the shell just squashed on the tip of his boot. So when people say that the spitfire was better armed than the ME109E it's true. 

 

The MGFF wasn't as much "bad" as the Hispano was a very good design. By the time they perfected it (Mk.II) they had an amazing gun, and with the Mk.V they had a gun that lasted them throughout the war and beyond. I think however that if they had found themselves in Luftwaffe's situation by the late war, they too would have found it somewhat lacking in power against heavy bombers.

Edited March 3, 2014 by 79_vRAF_Friendly_flyer

[Sternjaeger]

MGFF were not very good, not at all like the MG151. I have red of a spitfire pilot who got shot by a 20mm shell in the foot during BOB and the shell just squashed on the tip of his boot. So when people say that the spitfire was better armed than the ME109E it's true. 

 

Do you even know the difference between an MG-FF and a 151/20? The episode you described means nothing: it's likely it was an AP round that flew threw the cockpit and hit the tip of the pilot's boot. 

 

The Spitfire was NOT better armed than the Me109, and the fact that the RAF soon afterwards used the same configuration (MGs+cannons) of the Me109E on their Spit Mk.V should be testament of its superiority. 

[Bladderburst]

Difference: Higher velocity, higher rate of fire and bigger shell. Overall a better gun.

[MiloMorai]

 

The Spitfire was NOT better armed than the Me109, and the fact that the RAF soon afterwards used the same configuration (MGs+cannons) of the Me109E on their Spit Mk.V should be testament of its superiority. 

 

Not soon afterwards as cannon armed Hurricanes and Spitfires flew in the BoB.

 

The Germans gave away this so-called superiority with the Bf109F > 1 15mm cannon and 2 pee shooters compared to 2 20mm cannons and 4 pee shooters.

[Sternjaeger]

Difference: Higher velocity, higher rate of fire and bigger shell. Overall a better gun.

 

which one?

[Kurfurst]

The MGFF wasn't as much "bad" as the Hispano was a very good design. By the time they perfected it (Mk.II) they had an amazing gun, and with the Mk.V they had a gun that lasted them throughout the war and beyond. I think however that if they had found themselves in Luftwaffe's situation by the late war, they too would have found it somewhat lacking in power against heavy bombers.

 

There was nothing wrong with the MG FF, it was the lightest and most compact (weighting less than half that of the long barreled Hispano)  cannon of the Oerlikon cannon familiy (which included much bigger versions like the FFL, FS - these were happily used by Axis and Allied naval installations) and was extremely reliable (which the Hispano was just so-so). The dowsize was poorer ballistics and shorter effective range, but you could mount two of them for the weight of a single Hispano or larger Oerlikon, which was quite a factor with early fighters with relatively weak engines. And the gun still packed a pretty punch, given that cannons rely on the power of the explosive shell, rather than their muzzle velocity. When more powerful aircraft arrived, it was kinda natural that heavier and bulkier cannons were carried. Hint, hint - the Hispano itself is direct descendant of this cannon family, hence the drum magazine.

[CreepiJim]

Airborn weapon ballistics is a rather interesting topic. Light projectictiles do suffer from various issues also present on the ground, however some environmental factors greatly change the ballistics, not just for the better.

 

A light .30 cal projectile will be highly affected by cross wind and low energy retention. The ballistic coefficients were rather poor back in the days which made large caliber projectiles much more favourable. The size and weight, on the other hand, made it difficult to mount as many guns or with as many rounds, as the larger caliber systems. Low atmospheric pressures increase the v0 and flatten the trajectory for less time-on-target strafing runs.

 

The muzzle velocity was needed for small caliber projectiles to keep the energy output as high as possible, the energy retention (again due to low BCs) made them only good on short ranges. The penetration capabilities changed with different projectiles (AP rounds of different make and model) but are slightly in favour for the small caliber rounds with higher cross-sectional density (hence the later saboted rounds).

 

Cannons were a trade-off to achieve high destruction with explosive rounds with (usually) lower muzzle velocities resulting in a high flight trajectory which made long range shots challenging, especially leading the target.

 

The ballistic coefficients were better (more energy retention) but in the war the aerodynamics were not top priority for cannon rounds, so the form factor did not play a great role.

 

The armament question is beyond me, though, terminal ballistics on hard targets, too. A heavy HE projectile has a hard time penetrating a fairly armoured component, so there had to be a compromise between penetration capability and "payload" to detonate behind the armour plate. Nowadays this is easily acheived with depleted uranium (incendiary after impact) or tungsten carbide penetrator with an incendiary filler, sometimes titanium cores or phosphorous.

 

Large holes were always good, even without secondary effects. Many small caliber rounds did not really suffice to bring down fighter aircraft, cannons however suffer from restricted ammunition storage capacity in the fighter aircraft.

 

And as the history showed, larger is not always better (don't believe what she said!) becuase many large caliber cannons were fitted due to shortcomings of scientific evaluation of alternatives. An anti-tank gun on a plane only leads to a few rounds, high chance of structural damage due to recoil and low hit probability.

[MiloMorai]

There was nothing wrong with the MG FF, it was the lightest and most compact (weighting less than half that of the long barreled Hispano)  cannon of the Oerlikon cannon familiy (which included much bigger versions like the FFL, FS - these were happily used by Axis and Allied naval installations) and was extremely reliable (which the Hispano was just so-so). The dowsize was poorer ballistics and shorter effective range, but you could mount two of them for the weight of a single Hispano or larger Oerlikon, which was quite a factor with early fighters with relatively weak engines. And the gun still packed a pretty punch, given that cannons rely on the power of the explosive shell, rather than their muzzle velocity. When more powerful aircraft arrived, it was kinda natural that heavier and bulkier cannons were carried. Hint, hint - the Hispano itself is direct descendant of this cannon family, hence the drum magazine.

 

Good thing the Hisso was just so-so or there would have many more Bf109s shot down than there was historically.The lowly Spit and Hurricane, using inferior fuel, weak weapons and week-end warriors, managed to shoot down ~1650 Nazi German airplanes during the BoB.

[79_vRAF_Friendly_flyer]

A good cannon-armed fighter (either the Whirlwind or Beaufighter developed in time and in sufficient number or a reliable cannon for wing installation in the Hurries or Spits) would likely primarily affected the loss rate of the German bombers. Even the most cursory firing up of the old IL2 1946 indicate it would have been very bad to fly bombers.

Edited March 4, 2014 by 79_vRAF_Friendly_flyer

[79_vRAF_Friendly_flyer]

There was nothing wrong with the MG FF, it was the lightest and most compact (weighting less than half that of the long barreled Hispano)

 

Indeed, as I said, the MG FF was not a bad gun. The thing is, when you trim down a weapon as powerful as an auto-cannon for use in a flimsy, lightly built and armoured vehicle like a plane, you always have to compromise on something.

 

The MG FF was essentially a very light Orleikon, firing from an unlocked bolt (so that only inertia held the bolt in place until the shell had left the barrel), it was mechanically simpler than the Hispano. That primarily translated into a lighter, but as you noted more reliable, gun. To achieve that, the designers had to sacrifice some of the power of the round, translating to lower muzzle velocity and lighter shells. Considering aerial combat mostly took place over relatively shorter distances than the anti-aircraft Orleikon was designed for, it did not affect the gun much in it's intended role.

 

The Hispano's designer (Birkigt) decided to stick with the more powerful round, and made a heavier, more complex gun with a slightly lower ROF, but noticeable better shell trajectory. In it's intended role as a primary anti-bomber gun, that decision made sense.

 

With the limitations necessary when making guns for a single engine propeller plane, there is obviously no "perfect gun". Both the MG FF and Hispoanos were great guns in for their intended roles.

Edited March 4, 2014 by 79_vRAF_Friendly_flyer

[Wulf]

A very American-style documentary (I am not judging, only describing a certain style) on the 109 vs Spit debate. I post this video clip because at about 11' it gets interesting as they test a Browning 303 vs a 20mm cannon on an aluminium sheet. 

 

http://www.youtube.com/watch?v=BpTrygZfC-g

 

 

It's a bit academic but if you look at pictures of the left hand side of the MG (11.14), it doesn't even appear that it's a .303 Browning that's being used.  Looks a lot like 7.62x51 (NATO) to me.  The ballistics of the two cartridges are very close however.

[StarLightSong]

A Luft.  Target Lead lesson from the early WWII period.

 

 

 

 

There's quite a bit of common knowledge concerning hide penetration, bullet drop and recoli over various ranges concerning common rounds used for moose or bear hunting here in the North.

3006 vs 308 vs 3030 and WinMags with varying grains of propellant. I imagine the same info is readily available with regards Elk or Mountain sheep or whatever's hunted in your neck of the woods. Generally it takes a lot to get a big bullet going, with more reach if it's streamlined, that's going give you some kick but it will penetrate a thick hide and 6 inches of fat and rattle around so you're not wearing a brown bear like an uncomfortable hat.

 

If I had to level a rifle at metal skinned 'plane with fancy stuff humming inside -

Flat trajectory and high bullet speed good.

Explosive round with the above "crazy good".

Big ol heavy round with all the above "Thor's Hammer" good.

All of the above and a high rate of fire, "Dream Date" good.

All the above with a large magazine, "Take home to mom good."

I think some of the later Luft. cannons fulfilled much of the former.  So cannons for my fighter please.

____________________________________________________________________________________________________

Spent a few hours on the web following the cannon/ .50 issue and came to find a mostly cannon vs cannon endpoint of most discussions.

As per below.

info page with great links in the last 3 posts:

German Aircraft Cannon  http://www.ww2f.com/topic/2890-german-aircraft-cannon/

2 posts of data from some serious Devotees!

 

From Erich on WW2f.com (gun calibre, size weight magazine    round velocity

MG 17 7.92 1175 length 159 height, weight: 10.2 rounds: 1200 vm/sec 905

MG 131 13.1 1168 length 123 height, weight: 19.7 rounds: 930 vm/sec 710/750

MG 151 15.1 1917 length 190 height, weight: 41.4 rounds 700 vm/sec 850/1025

MG 151/20 20mm 1767 length 190 height, weight 42.3 rounds 720 vm/sec 695/810, higher rate in Fw 190A-8 variants.

Mk 103 30mm 2318 length 348 height, weight 145 rounds 420 vm/sec 860

Mk 108 30mm 1057 length 216 height, width: 222, weight 58 rounds 650 ( this is a bit high as normally via Sturmgruppen Fw 190A-8/R-2 and R-8 variants it would be 575 to 600. vm/sec 520.

 

Posted by Tony Williams . . .

Greetings, gentlemen!

I have examples of the all of ammunition calibres mentioned in my collection, plus a few oddities (20x105 MG 204).

The 20mm Hispano was more powerful than the MG 151/20, but not as fast-firing. The shells were heavier and penetrated better, but contained less HE, so they relied on fragmentation rather than blast to do most of the damage. As to which was more effective, it really depended on where they hit.

___________________________________________________________________________________________________________

 

 

 

So the debate seems to be more about types of cannons rather than cannons vs .50 if you can get cannons that is,

but yes, logistics matters, at a 3 US Sherman for every Tiger ratio - soon no Tiger Tanks left. WWII brought to you by Detroit.

[StarLightSong]

Closure!!!

 

Wanted to edit the above post and add this excellent "final word article" but the edit button is gone...

 

One more summary opinion from the "Devotee" forum above.

"the Mk108 3-cm was undoubtedly the 'best' for destroying bombers in daylight ( which is what it was designed for ). At night, or in fighter-to-fighter combat, the 20mm was 'best' and I'd reckon the Hispano over the MG151"

 

a bit more detail is considered below which "jives" with most of the WWII aviation enthusiast common knowledge and anecdotal info including the excellent performance of the Soviet guns.

 

and the  link that succintly deals with the question of weapon effectiveness.

 

http://www.quarry.ni...W2guneffect.htm

 

from the above site:

 

Left to right: 20x101RB, 20x105, 20x110RB, 20x110, 20x125, 23x152B, 30x92RB, 30x114, 30x122, 30x90RB, 30x184B

Left to right: 30x184B, 37x112R, 37x144, 37x145R, 37x165R (manually loaded), 37x195, 40mm caseless, 45x186, 57x121R

 

Gun Efficientcy, power to weight with accompanying ammunition.

 

"Most of the Soviet guns show up as being remarkably efficient, with scores of around 4, but the Hispano and the MG 151/20 also show up well, as do the simple MG-FF and Japanese Type 99 API blowbacks because of their light weight.

 

The American Browning .50 M2 is an undistinguished performer, particularly when compared with its closest competitor, the 12.7 mm Berezin. The relatively small incendiary content in the .50 API (0.9 g instead of 2 g) gives the Soviet round a flying start, which it adds to by its usefully higher rate of fire, then finishes off in style by being lighter as well, and thereby almost twice as efficient overall. The Browning also makes an interesting comparison with the Japanese Ho-5, which was basically the M2 slightly scaled up to take 20 mm cartridges.

 

It may appear that this low score of the .50 M2 is in disagreement with the satisfactory experience the USAAF had with this weapon. The answer to this apparent contradiction is that the .50 M2 proved very effective against fighters and (not too sturdy) bombers, if installed in sufficient numbers. Six or eight guns were specified as standard armament, resulting in a destructive power total of 360 or 480, at the cost of a rather high installed weight. Most American fighters were sufficiently powerful to have a high performance despite this weight penalty. Incidentally, the mediocre efficiency score of the .50 M2 is not only an effect of the low chemical content of its projectiles. Even if only the kinetic energy were considered, the efficiency of this gun would remain inferior to that of the UBS, B-20, ShVAK or Hispano, although better than that of the MK 108 or MG-FFM. To sum up, the preferred US armament fit was effective for its purpose, but not very efficient by comparison with cannon."

 

"A further validation of the calculations is provided by the outcome of tests by the USN, which stated that the 20 mm Hispano was about three times as destructive as the .50 M2. In the table linked below, the ratio between their scores is 3.3.

 

 

http://www.quarry.nildram.co.uk/WW2guneffect.htm

 

The outstanding performer is clearly the German 30 mm MK 108, which achieves ten times the destructiveness of the .50 M2 for only twice the weight. It makes a particularly interesting comparison with the MK 103, which fired the same M-Geschoss projectiles. The MK 103 gains an advantage because of its higher velocity, but loses most of it due to its lower rate of fire, then is finally eclipsed in efficiency because of its much greater weight. No surprise that the Luftwaffe considered the MK 108 their premier air-fighting gun despite its low muzzle velocity. The Me 262 jet fighter, with four of these guns clustered in the nose, completely outclassed the firepower of every other WW2 fighter."

[StarLightSong]

3 points discussed in the above thread addressed by a study or Kinetic vs Chemical damage in Cannon/ .50 calibre shells.

 

"1. The kinetic element of destructiveness is measured at the muzzle, not at combat range. The subtext of this argument is that the .50 Browning, having better ballistics than cannon, retains a higher percentage of its destructiveness at long range than cannon.

In fact, while it is true that most cannon shells slow down more quickly than the .50 calibre bullets, it is not true that their destructiveness reduces pro rata. As has already been pointed out in this study, much of the destructiveness of cannon shells lies in their HE/I content, which is not affected at all by the striking velocity as long as it is sufficient to actuate the fuze. So while both .50 bullets and cannon shells lose kinetic effectiveness with range (the cannon shells at a faster rate), in overall destructiveness (kinetic +chemical) most cannon shells actually lose effectiveness more slowly than the bullets.

 

It is also worth pointing out that most successful attacks in WW2 took place at fairly short ranges at which different projectile ballistics would not have had a major effect on destructiveness. During 1940 the RAF rapidly dropped the harmonisation distance for their fighter guns from 370 to 230m, and were annoyed that the narrow gun bays in the Spitfire's wing prevented them from harmonising the 20mm cannon down to their preferred distance of 180m (at which they did most ammunition effectiveness testing). Although successful attacks at longer ranges were possible, particularly against large, stable targets like heavy bombers (as the Luftwaffe discovered), it seems probable that the great majority of shoot-downs took place between 100 and 300m. This is often not appreciated by players of combat sims, who think that the ability to score routinely at ranges of 1,000m or more in their games reflects WW2 reality – it doesn't!

 

3. The shorter flight time of the .50 bullets, plus the larger number fired for a given weight of armament, greatly improves the hit probability of this armament by comparison with the slower-firing cannon, making shoot-downs more likely.

The first part of this criticism is undoubtedly correct, but the second part does not follow. The relative lack of effectiveness of the .50 bullets mean that it is necessary (on average) to score many more hits to shoot down a plane than with cannon armament. These two factors probably more or less cancel each other out.

 

As has already been observed, hit probability is also affected by many other things apart from gun performance: the quality of the gunsights, the location of the guns, the stability of the aircraft as the gun platform, and above all, pilot skill. These cannot be taken into account in a study of this type – there are just too many variables.

 

4. That the calculations understate the effectiveness of cannon in general, and large-calibre cannon in particular. This is partly because while a machine gun bullet relying in kinetic energy has to hit something vital to have an effect (or score so many hits close together that it shreds the structure) - it otherwise just makes small holes - a single cannon strike anywhere on the aircraft can inflict significant damage. It is also argued that a hit by one large cannon shell is more effective than hits by several smaller shells generating the same total damage score, as these will be spread across the aircraft instead of being concentrated at one point.

 

These points are valid. However, it is also true that cannon shells did not always explode when they hit – the fuze could sometimes fail to function – in which case they were reliant solely on their kinetic damage. Again, it seems likely that this would more or less counteract the criticism.

In conclusion, while it is admitted that some elements of the calculations – especially concerning the relative weighting given to kinetic and chemical damage – are open to criticism, in practical terms the results stand up quite well. Changing the method of calculation affects some scores but has surprisingly little effect on the overall 'order of merit' of the destructiveness rankings. Where it does have an effect, it is generally to boost the scores of high-capacity HE shells while reducing those of lower-velocity AP cannon shells and AP bullets, which is validated by the Luftwaffe's decision to focus on chemical rather than kinetic energy in developing their aircraft weapons.

 

To return to the obviously controversial question of the relatively poor performance of the .50 Browning: as has already been stated in this study, "the preferred US armament fit [of six or eight .50 HMGs] was effective for its purpose, but not very efficient by comparison with cannon". It is worth pointing out that for as long as the battery of .50s proved adequate against the targets usually encountered, there were strong arguments in favour of retaining the weapon, as the standardisation of production, supply, maintenance and training provided great logistic benefits by comparison with the plethora of different weapons fielded by the Germans and Japanese in particular. Of course, the USA did make some use of the 20mm Hispano cannon, but this was severely limited by production problems. . ."

 

http://www.quarry.ni...W2guneffect.htm

[Venturi]

You guys are funny, if in a lightweight fighter plane, you get hit by a bunch of stuff, you're going to feel it, whether it is .303 or 20mm. But,

 

A Luft.  Target Lead lesson from the early WWII period.

 

 

I'm sold, she certainly believes in 20mm!

[79_vRAF_Friendly_flyer]

Smashing cartoon!

[Sternjaeger]

yes, it has been said before, do not take the conclusions of Tony Williams as the ultimate word on the matter, as there are several factors that haven't been taken into account and which pertain to operational use of aircraft machine guns. 

 

Venturi, you can surely feel a 20mm hitting you, but you could probably get a burst of 303 without noticing, as their penetration is quite poor.

Smashing cartoon!

 

yep, that's from the famous Horrido! manual that was given to Luftwaffe pilots, and is available online.

 

Unfortunately I never found a translated version, so it's mostly a case of looking at the pics (which are pleasant!)