I have updated the article on WW2 aircraft gun effectiveness, to consider some of the criticisms made of the original study and to add some comparative ammunition photos. See: http://www.quarry.nildram.co.uk/WW2guneffect.htm

Tony Williams: Military gun and ammunition website and Discussion forum

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Tony Williams: Military gun and ammunition website

I've been playing around with this a bit lately. Something missed in the discussion is the target - attacker speed relationship. Rate of closure is an inverse expotential function that is modified by a trignometric vector for deflection. What all that means is if you are going really fast and the target isn't you don't get much time to shoot at it and, that if you double the speed difference you get about a quarter the shooting time.
Without giving away the whole plot of the paper, here's an example using the data presented in the tables at Mr. William's site:


The target is a heavy bomber moving at approximately 200 knots. Three firing aircraft are considered, an Me 262 armed with 4 x Mk 108 30mm cannon, a Fw 190A8 with 4 x MG 151 20mm cannon and 2 x MG 151 15mm guns and, a P-51 with 6 x M2 .50 machineguns. The Me 262 is moving at 550 knots giving a 200 m/s closure rate. The Fw 190 and P-51 are moving at about 380 knots giving a closure rate of about 100 m/s. The effective firing range is considered to be ½MV of the weapon minus 100 meters for the break-off distance from the target.
This gives the Me 262 a 150 meter firing zone for about 1 second of effective fire resulting in 40 rounds fired. The Fw 190 has a 275 meter zone and can fire for about 4 seconds giving 192 20mm and 120 13mm rounds fired. The P-51 has a 345 meter zone firing for about 5 seconds giving 450 rounds fired.
It is assumed in all three cases 3% of the rounds strike the target. For the Me 262 this results in 1 or 2 hits. For the Fw 190 5 or 6 20mm and 3 or 4 13mm strike the target. The P-51 gets 13 or 14 strikes.
The resulting damage is:

Me 262: 58 damage per hit = 58 to 116 damage
Fw 190: 16 per 20mm and 3.2 per 13mm = 90 to 109 damage
P-51: 4.6 damage per hit = 55 to 60 damage

The results clearly show that higher rates of fire and higher muzzle velocities result in significantly more damage against a target than slow firing low velocity cannon even when these do vastly more damage per hit. Of course, against a bomber this result is likely to skew to a greater degree in favor of the ‘slug thrower’ and skew away from such a gun when the target is a maneuvering fighter.
For fast moving aircraft, particularly jets, provision for very high velocity and fast firing guns is of paramount importance. These aircraft will be severely handicapped by a low velocity, short-ranged armament as well as by low rates of fire.

Some interesting points - and a few responses 'off the top':

I think that tactics may come into play here. For instance, ISTR reading that Me 262s used to slow down as they approached firing range against the bombers.

There is also the issue of gun location: the wing guns on the P-51 could not be concentrated at the point of aim at annything like the range of distances that you mention (unlike the primarily nose-or root-mounted guns of the German planes), so the percentage of hits could be expected to be lower.

The Germans determined that concentrated damage at one point is more effective than equivalent but dispersed damage from a lot of small hits - which favours the cannon.

In considering the benefits of velocity, don't forget that the Luftwaffe had the option of the 15mm version of the MG 151, but rated the 20mm version as considerably more effective.

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Tony Williams: Military gun and ammunition website

Of course, tactics play a role here. The most effective attack on a bomber is a "high side pass." This starts from the head- on position with the fighter above and to one side of the target. The fighter approaches to almost abreast the target then turns into it using a wingover (diving turn). The fighter approaches using this diving turn to lead the bomber in a deflection shot. This gives the bomber's defensive gunners a target that is closing on a curve requiring a deflection shot in return reducing the likelihood of effective defensive fire too.
As a note, the USN...ostensively the leading air service in deflection shooting having taught it in training since the mid 30's to their pilots...had really negative comments on the FW 190 in this respect; saying it made a really bad deflection shooting aircraft due to the low canopy and straight high nose.
Anyway, there is alot more to this than I put in at this point as I think everyone will acknowledge. As for the 262; if it slows down to get more shooting time it greatly increases its vulnerability to defensive fire and escorting fighters. It gives up its biggest advantage: speed.
As even the crude example provided shows the FW has the advantage over the P-51 in firepower. Yes, cannon are better so long as they are high velocity ones.
As for concentrated damage, MIL-HDBK 336 Vols 1 - 3 Aircraft non-nuclear survivability disputes this. Except for structural damage, only one of several ways to "kill" an aircraft most systems are dispersed throughout the plane. This makes it possible to 'spray' the aircraft and damage other non-concentrated systems causing a kill like control systems, fuel systems, etc. So, on the issue of concentration of damage once again it is a complex set of conditions that apply.
At this point, I was looking more at a basic set of assumptions that give a good "first approximation" set of results.

a high side on pass ? hmmm interesting must not be for the Luftwaffe though as they found through experimentation to make an attack on the rear of a US heavy slightly from above or slightly below, taking out the tail gunners position and then both engines on one side or the other of the heavy bomber.

Tony where have heard that Me 262 pilots slowed down to make a firing pass ? never heard thsi from any of the vets of JG 7 I have interviewed. the attack if it could be planned was porpoise like, nialing the belly turret and then right into the tail position and along the fuselage and into the engines inboard before passing, although we have continually probed the effectiveness of 3cm Minengeschoss the traveiling time from the rear was incredibly great for the 262 thus possibly 4 seconds of firing time. Attacking from the front with the jet would of been ridiculous

I almost fear to tread here, but from the many memoirs and accounts I've been reading recently my impression is that the high-frontal attack with wingover as described by T A was used against the 8th AF during 1943 but by 1944 the Luftwaffe had progressed to the rear attack as described by Erich....most definitely for the Sturmgruppen and the jets when they appeared.

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"Stand by to pull me out of the seat if I get hit" - Guy Gibson

Given the declining quality of pilots in the Luftwaffe, it would make sense that they would switch to an attack requiring little deflection shooting. When you add the unsuitability of the 190 in particular to low target deflection (the target is below the firing aircraft meaning you have to be able to see over the nose of your own aircraft) shooting this makes even more sense.

The point to remember is that there are trade-offs, as with any armament choice. Yes, a high-velocity 30mm would have been more effective than the MK 108, BUT the high-velocity MK 103 weighed twice as much and fired at only about two-thirds of the rate. So for the same weight as one MK 103 you could get two MK 108 which together would put three times as many shells into the air, and the Luftwaffe decided that this increased the hit probability sufficiently to make the MK 108 the better choice (except where they could only fit one gun anyway, such as an engine mounting).

Alternatively, if you wanted to keep the gun weight down and the velocity up, you had to go to a smaller calibre of cannon. Note that the Germans were developing both 20mm (high-velocity) and 30mm (low velocity) versions of the MG 213C revolver cannon at the end of the war, but the 30mm had priority as the 'bomber destroyer' - the 20mm was for ground attack. The Luftwaffe gained lots of experience in shooting down planes, and their preference was clear - calibre was more valuable than velocity (at least in WW2 fighting).

Erich I can't now recall where I got the info about the Me 262 slowing down from, but I certainly read it somewhere as I incorporated it into my novel 'The Foresight War', in the following brief extract:

"The jet streaked through the fighter cover, dived underneath the bombers which suddenly seemed to rush backwards past him, then he pulled up and shed speed rapidly to give time to aim."

I can assure you I wouldn't have invented that - I must have read it somewhere, but I went through so many books in researching that novel that finding the source would not be easy!

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Tony Williams: Military gun and ammunition website

I met Gunter Rahl (sp) at a bookstore in Seattle over a decade back. He would seem to agree with Tony.
He flew a 262, and was dam glad his flight got them instead of the Do-335. (That pusher/puller thing)
It was either going to be one or the other and nobody knew for sure until they got them.
He confessed to me his concern that there was no way out of that thing!
With the Me-262, he said that one pass sweeping the underneath of the wing of a B-24 would virtually assure bringing it down. He also said that doing the same on a B-17 would not, He said..."That was a bomber."
I talked about my old mans squadron with him, and he said Mustangs used to chase him back to his base, so he had to divert them (another direction) and turn back to land quickly (using his speed) and get to cover, sometimes out of fuel.
I also met a P-51 pilot who shot down "2" Me262's. This was while they were landing, out of fuel, but still in the air, and counted as an air-to-air kill. This could be considered murder, but since there is no murder in war, it's a ststistic.
Mark Twain says, "There are 3 kinds of lies in the world...Lies, Dam Lies, and Statistics!
About P-51 ammo, they switched from the hodgepodge assortment of incendary/ball/AP/tracer (and some other) to all Armor Piercing Incendary after combat expierences.
With tracer every fifth round (or so)for their 50 cals.

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There's one way to find out if a man is honest-ask him. If he says "Yes", you know he's a crook. Groucho Marx

From the rear and below, and only enough time to hit one wing. Sorry I didn't mention that before.
At least from the one Me262 pilot I talked to. I can't speak for everyone.

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There's one way to find out if a man is honest-ask him. If he says "Yes", you know he's a crook. Groucho Marx

just so you are well aware Günther Rall never flew the Me 262 in action, he test flew the bird, his responses are from fellow jet Offiziers. Rall was Kommodre of JG 300 the last several months of the war, a position that did not suit with him well nor with the men that served under him, some calling him incompetent.

My opinion is that Günther should of stayed with JG 52 flying the updated Bf 109G-10

The man I talked to never did give me his name, he said he was in the history books, thats all. I have a video of Gunter Rahl talking about "something" and I believe I recognized his face and voice. My assumption.
Whoever this man was, he looked alot like him, and our conversation was interrupted by some other American veteran groups harrassing him to come and talk at their reunion.
He told this individual that he was finished with that stuff, and if you wanted to hear about his exploits, he once again said that he was in the history books!
He got real "pissy" about being constantly asked to show up and speak so much that he no longer had his own life.
I returned to the book store 3 months later with my father so he could talk with him while they were both still alive.
My old man speaks broken German, as do I, so he was used as procurment while in Germany. While doing the commanders business in town he was asked by the locals..."Why are you here fighting your own people?". I related this to whoever this German pilot was, and he replied "Yah, Yah"
Small world.
This man was definately German, definately a pilot, and knew about everything that happened back then. He was willing to talk in an unpressured way one on one, but as most of us are, a little nervous to be center stage.

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There's one way to find out if a man is honest-ask him. If he says "Yes", you know he's a crook. Groucho Marx

well the gent could of been Rall but then again maybe not. Funny you mentioned about his not so kind attitude if it was him.............when I interviewed Rall some years ago I was very specific with his JG 300 days. He did not seem to want to talk about it or possibly avoiding it the best he could. Obviously some painful days with so many youth going to their deaths daily and he trying to get the Geschwader moved from spot to spot defending against US heavies, fighters and the Soviets to the east, never knowing which way was up. He was an intersting character and personally I was not too impressed, even though he claimed that he knew about every kill he made like a book in his mind.

sorry to ramble off top

I would guess that two things are pretty evident,
1 Seattle isn't far enough away to hide.
2 Ol Gunter baby, is a bit of a fabricator.
I left, I'll leave the guy in peace, if it was him. He paid more of a price than he should have for a life, and will for the rest of his life, if he's still around.
I enjoyed our chat, whoever he was. At least I didn't p_ss him off.
I did get to see him rip someone else a new one though. Sometimes it's good to be reminded that little courtesies, and blatant as_holisms, are both appreciated, and despised...in that order. World wide, and throughout the ages.
If he fought with that intensity too, God help ya.

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There's one way to find out if a man is honest-ask him. If he says "Yes", you know he's a crook. Groucho Marx