P-40 vs. ME-109

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Its easy to get sucked into a long debate about the types of ammunition different rates of fire and effective ranges and I am not against this in any way but sometimes its easier to stand back and look at the question in simplistic terms.
We know that the USN compared the 0.50 M2 against the 20mm Hispano II and summerised it as saying that the Hispano was three times more effective that the M2.
They would have done the test using all sorts of paramaters and criteria way beyond I could come up with and as a rule of thumb its a comparison worth remembering.

It also makes sense as it makes the normal 6 x .50 carried in so many US aircraft equal to the 2 x 20 carried in the Spitfire (ignoring the ineffective 4 x 303), both were effective against fighters and other Axis aircraft but would have needed beefing up had they been forced to face B17 type aircraft.
Its worth remembering that 2 x 20mm plus some MG's was a pretty common payload for a number of fighters and its unlikely that all those nations and designers would have made the same mistake. Generally these 20mm were not as powerfull as the Hispano II but were obviously effective enough.

The 2 x 20mm may have been more efficient as it was lighter than 6 x .50 but the US aircraft were able to carry this and have a performance to take on the opposition, so did it matter?
It did on the F4F4 but that is a much smaller aircraft and basically was overloaded. It needed to be lightened and the result was the FM2 which worked well.
 
Thanks for the opinions, bill. I've found some stuff I disagree with:

billswagger said:
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(Me: Hispano is as fast as .50 BMG):
This is debatable but what i think most people don't realize is that muzzle velocity is measured in the first few feet of fire.
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Guess it makes no difference if the MV is measured at muzzle, or during the 1st meter - the difference is under 5% still, ie. negligible.

Cannon rounds slow down faster at high speeds, or at least thats what was found early on.
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That's a generalization, and a moot point anyway. If a 20mm, 140g projectile has 880m/s initial velocity (= Hispano), it would not lose any speed when compared with .50 BMG (50g @ 900 m/s). Now we could take medium velocity German, Russian and Japanese cannons: those would be slower indeed, but no complains about that in respective air forces using them.
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Isn't that a little dubious that .50 had 3,5 greater effective range


While I agree about what you've said about German tests (thugh it was 2-5%, depending who shots), I disagree about what you say of remedies for the problem. Germans moved to 30mm, since it takes only 3-5 such shells to kill a bomber. The other benefit for having one-two bigger vs. more smaller cannons was that Me-109 could become a good bomber-killer with a single cannon (Fw-190 even better one with 2 such cannons), while the shortcoming was low MV, thus requiring a close-in shot. Benefit is also that it's way less expensive to produce/mount/maintain 1 MK-108, then 3-4 MG-151/20 in lieu.

We see lighter configurations on German fighters intended for air to air combat or dogfighting, MGs are typically part of that arrangement although cannons were also used for shots at closer range.
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German fighters carried 2 cannons from day one of WW2, while in cowls of both 109 190 13mm guns were barely crammed in, so I'd say they stucked with MGs because of necessity, not because MGs were preferred. Both Bf-109F and early Fw-190 were criticized by Germans for not having armament as heavy as Bf-109E, or contemporary Spitfire Mk-V.


When I talk 'cannons', I mean 'all-world' cannons, not only anglo-american products
The issue about US-produced Hispanos was that their product was mismanaged (in one or other way), not that all canons were not good.


Gun heating was sometimes the issue, but many RAF Luftwaffe planes did used their cannons high above
 
billswagger said:
Cannon rounds slow down faster at high speeds, or at least thats what was found early on.
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That rather depends on the particular MG bullet cannon shell and the particular MG bullet.
Two things affect how fast a projectile loses velocity.
1. It's shape, how pointy is the nose and shape of boattail, if any. It's form factor.
2. How much it weighs in relation to it's frontal area. It's sectional density.
With 12.7-13mm bullets going from 33-34grams to 46-48 grams we can see that they varied quite a bit as did 20mm projectiles which ranged from 79 grams to 130 grams.
In the case of the American .50 vrs the 20mm Hispano the /50 cal bullets had better shape but poorer sectional density. Consider that while ground level test firing may give one result with the air at 20,000ft offering about half the resistance the difference at that altitude would be much less.


Without knowing which cannon this statement means nothing. It could refer to the American 37mm cannon with it's MV of 610m/s. The trajectory on this was bad enough that the XP-54 was designed with a mechanism to tilt the 37mm guns in relation to the .50cal guns to keep the point of impact the same at various ranges. But then this is not the 20mm Hispano is it?

billswagger said:
We see lighter configurations on German fighters intended for air to air combat or dogfighting, MGs are typically part of that arrangement although cannons were also used for shots at closer range.
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The German MG 131 was designed to fit into spaces (or at least require little more room) than the MG 17 fit into. It used lighter, poorer shaped bullets and it's MV was 120-160m/s lower. A better match for the German cannon but not really in the same class as the American .50.


According to Tony Williams there was a difference. He claims the British never used American made guns in operational aircraft but converted a number of them to AA guns. Aparently the American made guns were not up to British standards.
 
tomo pauk said:
Thanks for the opinions, bill. I've found some stuff I disagree with:



Guess it makes no difference if the MV is measured at muzzle, or during the 1st meter - the difference is under 5% still, ie. negligible.
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Not so negligable when fireing at higher speeds. The 50 caliber was found to have a flatter trajectory than the 20mm and while flying at 300+IAS that was a huge advantage over cannon shots that slowed down faster.

I don't doubt that late war 20mm Hispano was on par with 50 caliber MV and trajectory.

Isn't that a little dubious that .50 had 3,5 greater effective range
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It should be more for both, but the context of "effective range" is defined as looking through a gunsight in the cockpit of a plane, as oppose to looking down the barrel or through a scope.
Shots of 50 caliber remained inside the site ring for 850yards. Shots of cannon fire remained inside the site ring for 250yards.
Cannon is a general word used to describe HE rounds, which included 20mm. The early war Hispano was not the best for maintaining velocity but it was on par with other cannons.

I actually was looking at some ballastic features of the 20mm, 50 caliber, and a 14.7mm. A lot of the trajectory is not only related to the projectile size and weight but the amount of propulsion composition in the casing. A 14.7mm weapon fired with a similar composition of a 20mm has a better trajectory and range. I would not confuse heavier round better range and trajecorty unless its also fired with more energy.
 
Shortround6 said:
According to Tony Williams there was a difference. He claims the British never used American made guns in operational aircraft but converted a number of them to AA guns. Aparently the American made guns were not up to British standards.
Click to expand...

Its a question of history and sources then, because even the British cannons were riddled with problems.
Also the 20mm Hispano was used along side 303s initially. They were reserved for bombers, where records indicate 4000 rounds of 303s being spent on individual aircraft. The 20mm was a necessity even if it jammed half the time.

The Americans were focused on getting higher MV and firing times from the gun, but couldn't get a reliable configuration that matched the capability of the 50 caliber weapon until 1945. Wasn't even possible until 1944, and combat ready by 1945.
They did have other installations of the 20mm, as well as the 37mm. but were not as popular as the 50 caliber for the air war.


Bill
 
Bill, the early Hispanos (French, UK MK.II) had greater MV then late-war Mk.V, so their drop was actually smaller. If you could point out a reliable source about bullet drop, it would be cool. Until then, I'll stick to the" heavier the bullet - flatter the trajectory" mantra (provided that MV and drag coefficients are nearly the same)
 
I would be very surprised if the 20 mm had as good a ballistic coefficient or sectional density as did the 50 BMG. The 50 BMG was outstanding in both regards. Snipers have used the 50 BMG to make kills at one mile and that was with the M2. The table in "America's Hundred Thousand" shows the 20 mm to have a slightlly higher MV than the 50 BMG but and I am guessing, because I don't know the BC of the 20 mm round, I think the 50 BMG round would soon catch and surpass the 20 mm. Another however is though that the difference in trajectory of both rounds is probably not tactically significant because ranges were generally in the 300 yard area and pinpoint accuracy was not necessary or possible. The British were not able to equip their bombers with the 50 BMG, although it would have been desirable to do so, because of a shortage of the guns, until near the end of the war, according to a book I have. I suspect that the Spitfire would have gotten 50 cals in late 40, 41, o4 42, if they had been available. The Eastern front had no heavy bombers but it did have Russian medium bombers and ground attack planes that were heavily armored. In the early war, the German fighters had cannon because the MGs mounted were the puny 30 cals. Later those 30 cals were supplanted by the German version of the 50 cal, likewise on the A6M. The facts are that the M2 and it's round were available, tested, reliable and were found to be more than adequate for the job of knocking down the opposition during WW2. I wonder how many of us on this forum have tried to read extensively about aerial gunnery in WW2 and have reflected on how difficult it must have been to get any hits at all on an EA. The 50 BMG equipped fighters with four, six or eight guns, with a high ROF and relatively long firing times, gave American pilots a better chance to get hits and obtain local air superiority over enemy fighters. That is the bottom line.
 

There is a ww2 article on this forum that goes into all those details but i'm unable to locate it.

Just to use an example:

Same gun fires 20mm and 14.5mm.

The effective range of the 20mm is >1500m
the 14.7mm effective range is >2300m

The muzzle energy is nearly the same yet you get more range out of the 14.7mm.

There are also many variants of the Hispano and the Mk V was the only one that matched firing time and the velocity of the M2.
A plane diving on its target at 400+mph also needs to pull deflection and sometimes at ranges where the 50 cal was percieved as better because it retained its energy where the 20mm fell away.

It is hairsplitting, if you figure a pilot is good enough to anticipate where his shot needs to be with sufficient gunnery training. But there are other reasons for using the 50 caliber over the 20mm.


The Big One...

The 20mm is, however, recognized as the smallest projectile capable of the biggest pop. So for HE rounds, 20mm is going to be the most efficient.

You could probably Youtube this gun and get more qualified information.


Bill
 
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sure that a 14.5 at 1080 m/sec has more range of 20 at 720 m/sec, but the .50 it's not the 14.5 and the german 20 mm is not the hispano 20 mm. put the 50 and the 20x110 at 890 and 830 m/sec and easy that the range difference it's limited and useless in air fight not fight at so long range 300 meters are already good range, so pratically there is no large difference also with a 20x82 at 720 m/sec.
 
I'm with Tomo: Given the same bc and the same mv the gun firing the heavier bullet will have a flatter trajectory. Heavier rounds bleed of speed slower than lighter rounds that is a fact. Of course the ballistic coefficient is also important, but so far I've not seen any evidence suggesting its role is as important as combination of the other factors. If someone has conclusive evidence that proves otherwise feel free to show.

The Mechem is a bad example to prove your point as the MV is 300 m/s faster for the 14.5mm version. Or to put it relative, it is 1.5x that of the 20mm version. Which is actually interesting as the 14.5mm has also almost exactly 1.5x the range. I know its not really a linear connection but you could speculate that both rounds fired at the same mv would likely have very similar range. Also, being an anti-material sniper rifle, i guess effective range has another definition here than it has with aircraft mounted guns.
 
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The Hispano 20mm did not have the ballistic co-efficiency of the .50 cal. The 20mm Hispano rounds had a poorer shape but they did have a higher sectional destiny which helped balance things out.

See this bore sighting chart for a P-38

http://www.zenoswarbirdvideos.com/Images/P-38/38BSC.gif

While the 20mm has a bit more arc to it's trajectory but staying within a few inches of the 50cal from 0 to 500yds means that for practical purposes there really wasn't any difference.
 
Since Vicenco pointed out the flaws in 14,5mm vs. 20mm comparison, I'll add that Russians necked-up their 14,5mm to 23mm and use (along with half of the world) the new cartridge from from 1944 'till today. As aircraft weapon's cartridge, indeed
 
What you just said, riacrato, is not really true but the 20mm round may not have the same BC because of it's shape. If the two projectiles have the same BC then their velocities and trajectory down range will stay the same. An example: 45 cal 500 grain round nose bullet, BC is .297. MV is 2500 fps, zeroed at 200 yards, ar 500 yards the bullet has dropped 76 inches. 35 cal 250 grain round nose bullet, BC is .296. Zeroed at 200 yards, at 500 yards the bullet has dropped 75 inches. All info from Hornaday Handloading Guide. Heavier rounds do not necessarily bleed off speed more slowly than lighter bullets. It depends on, essentially how streamlined the bullet is. The 20 mm projectiles I have seen pictures of have a blunter tip than the 50 bmg has and the ojive looks "fatter" and thus not as streamlined. I would be surprised if the BC was as high. The 50 BMG has a BC in the area of .700 or so, I think.
 
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I can't really get into complicated discussions on bullistist nor have the time to back up what i know with every article i've ever read.

Trajectory has more to do with speed than weight. A faster bullet has less drop. Agreed, heavier bullets hold speed better if they have similar BC, mV In effect they have less arch over the length of the shot as the lighter round slows down. 303s had a flatter trajectory than the 50 caliber until they slowed down.

Now there is a significant difference at firing a gun from a stand still position than at 300mph. Consider for a moment that bullets travel at supersonic speeds where slight variations in coefficients makes for dramatic differences over the range of the shot even at 300 and especially over 500 meters. Then factor in deflection and turning.

The 20mm was found to slow down faster than the 50 caliber. This effects arch, (faster bullets less arch) Agreed, heavier bullet has more mass and penetrates armor better.

I have to agree that the 20mm did not have the same BC as the 50 caliber.

What effected it more as a gun platform for long range shots at high speeds was this fact of speed (retention), and firing time. It still made a great gun for shots at closer range and at moderate deflections. It was still shunned for its reliability issues.



Bill
 
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billswagger said:
303s had a flatter trajectory than the 50 caliber until they slowed down.
Click to expand...

what 303 had a higher velocity than the American .50?


True, but since ALL bullets fall at the same speed (32ft/sec^2) we can assume that two bullets with close to the same initial velocity that have the about the same trajectory will have similar times of flight to the distances shown in the trajectory chart. This also means they had similar ballistic co-coefficients.
billswagger said:
The 20mm was found to slow down faster than the 50 caliber. This effects arch, (faster bullets less arch)
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It may very well have but it didn't slow down enough to make much practical difference and any normal air to air range.

Please look at the P-38 sighting-in and trajectory chart I posted a link to. staying within 6in and usually less of the .50 cal bullets to 500yds (and/or beyond) means it could not have been that bad. Either your 250 yd figure applies to some other gun than the 20mm Hispano or this sight-in Chart is bogus.

billswagger said:
It was still shunned for its reliability issues.
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Only by the US. The British guns seem to have worked a lot better.
 
Question(s): At what actual ranges did fighter pilots open fire? IIRC between 200 and 300 yards. Does a small difference in velocity and drop even matter at such a short distance? And was armour penetration even an issue for cannon shells? I thought they were supposed to destroy the airframe with their explosive charges, not punch through armor like a machine gun bullet.
 

Small differences in the velocity and drop from the guns of single firing aircraft are not going to matter.

Larger differences will matter as in the American 37mm at 2000fps and the cowl mounted .50s at 2800fps+.

With the target moving at 450-600fps having the shells/bullets arrive even at the same point in space but at different times doesn't do much good.

If one sides fighter planes have guns that have a shorter time of flight to distance "X" by say, 20% than the other sides then the first side will have an overall advantage in deflection shooting and perhaps in range.

Of course if the difference between the different sides armament was only 5% then it might be too small to notice.
 

I saw it, and it shows bore sighting. The 20mm needed more velocity to have the same trajecory as the 50.
It slowed down faster, and did make a significant difference for air to air combat because as the plane gets faster more air resistance slows the bullet and drag coeficients increase dramatically. Looking at bore sighting doesn't always reveal this fact.
I find it odd they didn't use 20mm for all of the P-38s guns. Could it have been the ballistics properties i'm talking about.

And the british had jamming issues with this gun, but they made it work for what they had to do. They did fix these issues by the Mk V Spit but the amount of problems seems to be down played because the Spitfire saved Britain.

The point of the discussion is really irrelevant when shooting at 200m range, it is splitting hairs (there said it again) and level shots and slow speed fights at these ranges make little difference,


However a P-47 diving over 400 mph and firing at 30 degrees deflection is going to favor the flatter trajectory (speed retention).
You just figure at 200m, 200mph a couple degrees drop is of little consequence but at 400mph in a turn those effects are augmented. Those couple degrees could now be as much as 5 or 10 degrees at higher speed and augmented more so by the degree of the turn and the speed.
So the P-47 pilot may have to pull an additional 10 degrees (maybe more) to correct for speed loss of using 20mm over the 50 cal. And i call it speed loss to not be confused with trajecory which i think refers more to a calibers characteristics when fired at lower speeds and moderate deflections.



Bill
 

you're right I mixed up bc and form factor.

bill, I thought the M2 had a slightly faster mv than the Hispano. In any case, the difference both in mv and ballistic performance is very, very slim.
 
billswagger said:
I saw it, and it shows bore sighting. The 20mm needed more velocity to have the same trajecory as the 50.
l
Click to expand...


It also gives the trajectory figures to 500yds. How many inches above and below the line of sight.

With the 20mm starting 3in below the lower .50 cal guns it rises to meet the .50 cal at 300yds and doesn't fall below the .50 until after 400yds and is all of 1in low at 500yds.

Does it have the same trajectory as the .50? NO
Is it loosing velocity faster than the.50? YES
Is it going to make any practical difference under 600yds? NO
Trajectory difference are less than the normal dispersion of the guns/ammo.

The higher above sea level the firing takes place the less difference there is between the two. With the air density at 20,000 being about half that a sea level they will both slow down less but over a given distance the change should not be as great as at lower altitudes. Given that initial velocity's are only 3-7% higher than the 20mm for the .50 I am just not seeing the huge disadvantage for the 20mm Hispano.

By the way, thanks for this one, it sure made me laugh.

"And the british had jamming issues with this gun, but they made it work for what they had to do. They did fix these issues by the Mk V Spit but the amount of problems seems to be down played because the Spitfire saved Britain."

Since the MK V came out in the Spring of 1941 even if we tack on about 8 months it means the British had the problem solved BEFORE PEARL HARBOR

And of course all those squadrons equipped with cannon armed Beaufighters, Mosquitoes, Typhoons, Hurricanes and other aircraft played down their problems with the Hispano to help save the Spitfires reputation.
 
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