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

[Glider]

The result doesn't change much

To compare the rounds
one 20mm projectile weighs 129 gm and has an HE/I content of 8.8% giving 11 gms of explosive per round
one 0.5 mm projectile weighs 43 gm and has an HE/I conent of 2% giving 0.86 gms of explosive per round
Clearly this is a huge advantage to the 20mm.

Applying this to the percentage chance of a hit as you posted at 10% which was the least favourable result for the Panther

For 10% probability of a strike per projectile:
Out of 47 attempts the F9F has a 96% probability of 2 or more rounds hitting.
Out of 125 attempts, the F-86 will have 7 rounds hitting (97%).

The Panther has 2 x 11 gms of explosive on the target = 22 Gms
The F86 has 7 x 0.86 gms of explosive on the target = 6.02 gms
Basically this is still a 366% advantage to the Panther.

 

[davparlr]

Dave


The comment that one 20mm was equal to 3 x 0.5 was a general statement applying to the weapon, not one 20mm hit was equal to 3 x 0.5 hits. My understanding would be that he additional chance of obtaining a hit would have been factored into the equation. To put it another way the additonal chance of a hit would be more than 3 to 1 in the F86 favour due to the larger number of projectiles fired but the impact of a 20mm hit would be significantly higher.

Not likely since the probability of a strike is a variable depending on many other variables such as distance and gun sight. Most likely the analysis was made against a fixed target at a specific range. Once the baseline ballistics is determined and the damage measured, the impact of the other variables can be easily calculated. It is possible that the test was run on AP rounds and not explosive rounds, but I certainly would be surprised if they decided on weapons selection without including this very important factor, and I think this would have been brought up if it was not. This was a very high powered meeting; one of the participants at the conference was a C. A. Lindbergh, representing United Aircraft.

I don't really understand the last sentence. The probabilities I generated was for a one second burst with varying probability of accuracy.

Also, since probability of strike is function of accuracy, the effectivity of the gun is a variable, but not the round. As accuracy increases the 50 cal is landing more rounds per 20mm round so the effectivity of the 50 changes but the 20mm does not.

The Northrop armament engineer I mentioned earlier that was proposing a 50 cal Gatling for the F-5 stated that the penetrating power of the 50 was an advantage in combating jet aircraft.

 

[davparlr]

error duplicate post

 

[Shortround6]

Not likely since the probability of a strike is a variable depending on many other variables such as distance and gun sight. Most likely the analysis was made against a fixed target at a specific range. Once the baseline ballistics is determined and the damage measured, the impact of the other variables can be easily calculated. It is possible that the test was run on AP rounds and not explosive rounds, but I certainly would be surprised if they decided on weapons selection without including this very important factor, and I think this would have been brought up if it was not. This was a very high powered meeting; one of the participants at the conference was a C. A. Lindbergh, representing United Aircraft.

Which important meeting? the Navy Requested 23,326 T-31 20mm guns on the 12th of February 1944, this is the gun that wound up standardized as the M3 Hispano. According to Chin "ALL" future Navy aircraft designs (at the time) would use this gun. This predates the fighter conference by 8 months?

Given equal gun sights there shouldn't be much difference in accuracy. At practical ranges there is little difference in either trajectory or flight time. At 600yds the 20mm Hispano with it's "poorly" shaped projectile has it's first round arrive about the same time as a .50 (firing at 800rpm) has it's second round arrive. According to the P-38 trajectory chart the two guns were within inches of each other to 500yds. The 20mm shells, starting 7 in below the upper .50s hit at the same height (or within an inch) by the time the range was 350-500 yds. you would have to be well beyond 600yds to get any real difference in trajectory. And the higher you go into thinner air the less difference there is.

Also, since probability of strike is function of accuracy, the effectivity of the gun is a variable, but not the round. As accuracy increases the 50 cal is landing more rounds per 20mm round so the effectivity of the 50 changes but the 20mm does not.

This makes no sense. why is the "accuracy" of the 50 cal increasing but the 20mm is not? a better gun sight would affect the accuracy of both guns. proportions may change a bit but a better sight is not going to do zero for the 20mm hit probability if makes any significant change to the .50.

The Northrop armament engineer I mentioned earlier that was proposing a 50 cal Gatling for the F-5 stated that the penetrating power of the 50 was an advantage in combating jet aircraft.

This guy either needed a new job or he was not referring to the standard .50 Browning ammunition. The M39 cannon in the F-5 did not use Hispano ammunition. It used the same 20 X 102 round used in the Vulcan gun. a bit shorter than the Hispano but fatter, it propelled a 101 gram shell at 1030m/sec and 53,600 joules of Muzzle energy. design an AP round for this thing and you could have had penetration a .50 cal could only dream about. The 20mm round having about 21% more joules of energy per sq. cm of target area.
In WW II the Hispano 20mm Semi AP HE round could penetrate about the same amount of armor as a .50cal AP round but carried 10 grams of HE while doing it. 20mm AP rounds (solids) went through a lot more than .50 cal AP rounds.

Late war and post war there were a number of high velocity .50 cal rounds being played with, including necking the M-39/Vulcan 20mm case down to .50 cal. That might have had some very good penetration but it is hardly the .50 cal Browning round.

 

[Glider]

Taking the points one at a time,

Not likely since the probability of a strike is a variable depending on many other variables such as distance and gun sight. Most likely the analysis was made against a fixed target at a specific range. Once the baseline ballistics is determined and the damage measured, the impact of the other variables can be easily calculated. It is possible that the test was run on AP rounds and not explosive rounds, but I certainly would be surprised if they decided on weapons selection without including this very important factor, and I think this would have been brought up if it was not. This was a very high powered meeting; one of the participants at the conference was a C. A. Lindbergh, representing United Aircraft.

My copy of the book is out of my reach at the moment so you could be right but my memory was that it was a general statement not a specific breakdown. I do agree that your probability of a hit was done on the variables you mention however using those calculations. However my posting 81 shows a very significant advantage to the 20mm which far outweighs the additional hits obtained by the 0.5 which has to rely on hitting a vulnerable part whereas the 20mm is almost certain to do damage wherever it hits.

I don't see the attendance at the conference of C. A. Lindbergh being of relavence to this as he isn't a gunnery expert.

I don't really understand the last sentence. The probabilities I generated was for a one second burst with varying probability of accuracy.

I was trying to say that the despite the additional hits of the 6 x 0.5 something that I do not doubt, the additional KE impact of the 20mm coupled with its much higher explosive content, still resulted in a 3 to 1 advantage.

The Northrop armament engineer I mentioned earlier that was proposing a 50 cal Gatling for the F-5 stated that the penetrating power of the 50 was an advantage in combating jet aircraft.

No doubt he believed what he said but history has proven him wrong. The US went to 20mm as Europe went to 30mm, now the newest guns are in the 25 - 27mm band no one, of any nation, has ever gone back to the 0.5.

 

[gjs238]

Yes and no, some of decisions were incompetent. the story of the US 20mm Hispano is a long and sad one. Some ordnance officials refused to change earlier decisions on details like chamber length ( a difference of 1/16 of an inch) no matter how many demonstrations showed it was wrong until guns were stacked in warehouses by the 10s of thousands with no takers because of the resulting poor reliability. In that case the decision to stick with the .50 rather than try to use defective 20mm guns was the right one. Bur it wasn't a question of sticking with a gun that was "good", it was a question of sticking with the lesser of two evils. a gun of adequate power and reliability (many early .50 cal installations weren't that good but that was the installation and not the basic gun) vs a harder hitting but much lower reliability gun, and again the lower reliablilty was pretty much the ordnance depts own doing, British guns (with the shorter chamber) being much more reliable than the American ones.

Is this what was used in the P-38? Do we know how they performed in the P-38?

 

[gjs238]

The M60 was a mixed bag, it did some things right and got some things wrong and what was wrong was stupid stuff that shouldn't have been. One thing was that on early versions it was possible to assemble the gun with the gas piston in backwards, gun would fire one shot and stop. Can be gotten around by training (somewhat) by why not make the gun a little more soldier proof to begin with? another thing was that the barrel, gas cylinder and bi-pod came as a one piece unit. Carrying a spare barrel meant carrying a spare bi-pod. Now the bi-pod did give the gunner (or his assistant) something to hang onto while changing the barrel but it also meant the gun flopped on the ground when the bi-pod was removed. An asbestos glove was part of the barrel changing gear (according to the book). one cold over look such things on a WW I or 1920s machine gun. On a 1950s machine gun it leaves you wondering where the guys who approved it it were hiding for the last 20 years. An other feature )(not) was that the replaceable barrel had a fixed front sight. Bren guns had movable front sight sights. two or more barrels could be zeroed to the same point of impact using the same rear sight settings and the barrels swapped in combat with little or no change in impact with no work by the gunner. The M-60 required the gunner to know (or record in a pocket notebook) the rear sight settings for each barrel and change the zero setting on the sight each time the barrel was changed. Again,not a good feature on a a 1950s gun. There are a few other details that were less than world class.
All in all if leaves one less than impressed with some of the personnel in the ordnance dept. others may have done a very good job on other projects but US Ordnance was certainly far from infallible at times.

I thought it was developed from (or at least inspired by) the FG42 and perhaps the MG42. Sounds like something got lost in translation.

 

[gjs238]

While the M-4 was a world class tank in 1941 (initial design) and 1942 and while ordnance tried the decision makers screwed this one up. Depending on you opponent NOT to upgrade his tanks for several more years is NOT smart. The decision to upgrade the Sherman (even if they didn't go for the M-26) should have been made sooner. Much like the Russians upgraded in the T-34 in early 1944.

Was the issue really one of "upgrading" the Sherman, or switching from a medium tank to a heavy tank. At the time, I thought US Army doctrine favored medium tanks, with anti-tank guns and tank destroyers meant to tackle enemy heavy tanks. So I suppose the Sherman did was it was designed to do, be a medium tank.

 

[Shortround6]

Is this what was used in the P-38? Do we know how they performed in the P-38?

In the P-38 the gun was held in a heavy cradle that helped the reliability somewhat. It also added weight that does't show up in most tables. The British never issued an american made gun for combat.

 

[davparlr]

Which important meeting? the Navy Requested 23,326 T-31 20mm guns on the 12th of February 1944, this is the gun that wound up standardized as the M3 Hispano. According to Chin "ALL" future Navy aircraft designs (at the time) would use this gun. This predates the fighter conference by 8 months?

Given equal gun sights there shouldn't be much difference in accuracy. At practical ranges there is little difference in either trajectory or flight time. At 600yds the 20mm Hispano with it's "poorly" shaped projectile has it's first round arrive about the same time as a .50 (firing at 800rpm) has it's second round arrive. According to the P-38 trajectory chart the two guns were within inches of each other to 500yds. The 20mm shells, starting 7 in below the upper .50s hit at the same height (or within an inch) by the time the range was 350-500 yds. you would have to be well beyond 600yds to get any real difference in trajectory. And the higher you go into thinner air the less difference there is.

I always assumed the accuracy of the two weapons the same.

This makes no sense. why is the "accuracy" of the 50 cal increasing but the 20mm is not? a better gun sight would affect the accuracy of both guns. proportions may change a bit but a better sight is not going to do zero for the 20mm hit probability if makes any significant change to the .50.

The accuracy, ie, probability of a hit per projectile, is equal for both the 20mm and 50cal, however the faster firing weapons lands a proportionally greater number of rounds as the accuracy goes up.

For a probability of strike per projectile of 2%, the gun firing 125 r/s will land four rounds while the gun firing 47 r/s land two, or twice as much.

At a probability of strike per projectile of 5%, the gun firing 125 r/s will land slightly more than five rounds while the gun firing 47 r/s lands two, or over two and a half times as much.

At a probability of strike per projectile of 10%, the gun firing 125 r/s will land seven rounds while the gun firing 47 r/s lands two, or three and a half times as much.

At a probability of strike per projectile of 12%, the gun firing 125 r/s will land over nine rounds while the gun firing 47 r/s lands two, or four and a half times as much.

This is statistics and is independent of caliber of the gun. So, say, and the range decreases at an equal rate, the gun firing 125 r/s will increase strike strike energy at a faster rate than the gun firing 47 r/s.

 

[davparlr]

Taking the points one at a time,
My copy of the book is out of my reach at the moment so you could be right but my memory was that it was a general statement not a specific breakdown. I do agree that your probability of a hit was done on the variables you mention however using those calculations. However my posting 81 shows a very significant advantage to the 20mm which far outweighs the additional hits obtained by the 0.5 which has to rely on hitting a vulnerable part whereas the 20mm is almost certain to do damage wherever it hits.

Do you have any 20 mm and/or 50 cal ballistics data. I am confused by the Navy comment on kinetic energy at a 500yd target as the 20 having 2.5 times the 50 cal. yet the gun having three times the horsepower. I can only believe that ballistic changes would cause this, or my lack of understanding.

Certainly, in ww2 the HS 20mm was superior in performance where two 20s balance six .50s, except when a gun jams where 50% of the firepower of the 20s would have been lost, and its inclusion would have improved performance because of reduced weight. However, in the book and historically, there seem to be no great enthusiasm among the combat commanders or the war fighters to replace the 50 in the Navy, whose tech staff did prefer it and did update after the war, and certainly in the AAF. This may have been due to poor performance of the M-2 cannon. Also, as far as I know, there seemed to be no great enthusiasm with the British, who had experience with the 20s and had a better cannon, to upgrade their F4Fs, P-51s, F4Us, or F6Fs, to 20mm even though they did upgrade the P-51 with other weapons(I believe a rocket launcher), the Malcolm hood and test advance engines, and clip the wings of the F4Us, all to improve performance. I am being redundant here with another thread.

I don't see the attendance at the conference of C. A. Lindbergh being of relavence to this as he isn't a gunnery expert.

I agree, I just included that because he was highly respected aviator and technical adviser and his presence was kind of an indicator of the high level expertise that were in attendance. I also thought it was interesting that he was in attendance.

 

[Shortround6]

Apparently, according to Chin, the Navy wanted the 20 mm from the word go. What they wanted and what they got seem to be two different things. With 6 early drum feed Hispanao guns going to Brewster to be fitted to F2F-3's in 1941, it kind of points to were some of the Navy's interest lie. The ability of most Hellcats to mount a 20 mm in the inboard gun bay ( even if not often taken up) also points to the Navy's intent as do the trails installations in the Corsair.
With ordnance dept mucking up the production of the 20mm the continued use of the .50 doesn't show desire, it shows necessity. Desire is again shown by the Dicision to order the M3 20 mm gun inn quantity 8 months before the fighter conference and well before the Kamakazi threat became known.

 

[tomo pauk]

If I may cut in.

Perhaps we need to make sure about nomenclature.
My take is that USN estimated that one 20mm (Hispano) cannon is equal in aerial combat as 3 .50 cals. So did they mean kinetic energy, or (horse?)power, or whatever scientific metric? Nope, just plain, and, IMO, fairly precise estimate of a weapon's worth in combat. Further, the kinetic energy is a factor in aerial combat, but so is the explosive payload. And a projectile carrying payload is far less susceptible to the loss of velocity over bigger distance, than a bullet that relies on speed to make damage.

As for Navy tech staff not prefering the cannon over HMG:
- that declaration could use some good source
- what should be a reason for major update of WW2 left-overs?
- the Panther used cannons in Korean war, so quite soon after WW2 ended

The jamming issue US produced 20mm cannons had was not shared with 20mm cannons other countries were producing - again no proof that cannon is a worse choice.

Wing clipping and rocket launchers were better choice than full-span wings of Corsair (would'nt fit in hangers) and no rockets at all. As for Malcolm hood, it took only one per plane (and not all the bird-cage Mustangs got it), unlike the cannons, that were 4 needed.

added: 4 cannons 'equals' 12 HMGs in combat - think Navy knew what they wanted. And in (some) post war F4Us that's what they got, let alone the jets.

 

[Glider]

Do you have any 20 mm and/or 50 cal ballistics data. I am confused by the Navy comment on kinetic energy at a 500yd target as the 20 having 2.5 times the 50 cal. yet the gun having three times the horsepower. I can only believe that ballistic changes would cause this, or my lack of understanding.

Certainly, in ww2 the HS 20mm was superior in performance where two 20s balance six .50s, except when a gun jams where 50% of the firepower of the 20s would have been lost, and its inclusion would have improved performance because of reduced weight. However, in the book and historically, there seem to be no great enthusiasm among the combat commanders or the war fighters to replace the 50 in the Navy, whose tech staff did prefer it and did update after the war, and certainly in the AAF. This may have been due to poor performance of the M-2 cannon. Also, as far as I know, there seemed to be no great enthusiasm with the British, who had experience with the 20s and had a better cannon, to upgrade their F4Fs, P-51s, F4Us, or F6Fs, to 20mm even though they did upgrade the P-51 with other weapons(I believe a rocket launcher), the Malcolm hood and test advance engines, and clip the wings of the F4Us, all to improve performance. I am being redundant here with another thread.

I don't have the ballistic details of the 20mm vs 0.5 but as has been mentioned the P38 didn't have a problem with ballistics. The M3 is a different weapon I know with a higher MV which is a factor in ballistics, but a more important factor is the relationshp between the weight of the projectile and the cross section of the projectile. This factor is always in favour of the larger calibre weapon. Which is the best I don't know but would expect them to be close. Either way as has been stated on other postings the fire control radar on the aircraft probably make the difference almost negligable.

The USn were keen on including the 20mm. All F6-F5 fighters could be armed with 2 x 20mm and 4 x 0.5, the fact they weren't was down to the poor reliability of the US 20mm. Also I believe some Corsairs were armed with 20mm towards the end of the war.

The RAF/FAA didn't rearm their US aircraft I agree probably for the same reason that the USAAF didn't, why should they it was good enough for the job that they had to do. Why go to all the trouble when the original was good enough and you need them ASAP?.

I don't think the P51 used rocket in action but could be wrong, the Malcolm hood was needed as the original birdcage wasn't good enough and the F4U's had their wings clipped so they could fit inside the RN carriers whose hangers had less headroom than the USN carriers.

 

[davparlr]

If I may cut in.

Perhaps we need to make sure about nomenclature.
My take is that USN estimated that one 20mm (Hispano) cannon is equal in aerial combat as 3 .50 cals. So did they mean kinetic energy, or (horse?)power, or whatever scientific metric? Nope, just plain, and, IMO, fairly precise estimate of a weapon's worth in combat. Further, the kinetic energy is a factor in aerial combat, but so is the explosive payload. And a projectile carrying payload is far less susceptible to the loss of velocity over bigger distance, than a bullet that relies on speed to make damage.

I understand what you are saying but kinetic energy is also part of the energy equation and cannot be dismissed lightly.

As for Navy tech staff not prefering the cannon over HMG:
- that declaration could use some good source

I said this poorly "replace the 50 in the Navy, whose tech staff did prefer it and did update after the war". I meant to say that the tech staff preferred upgrading the 50 to 20 mm and did update after the war.

- what should be a reason for major update of WW2 left-overs?

Oct. '44, some of the most vicious and deadly fighting using these "left over aircraft" was yet ahead for the allied forces in the Pacific, and the Navy was about to field the most powerful fighter it would field in the war, the F4U-4, with 50s.

- the Panther used cannons in Korean war, so quite soon after WW2 ended

With the F4U-4C it tried out the American gun, I think, and it was a failure. The Post war F4U-5 also came with 20mm, but I don't know which one.

The jamming issue US produced 20mm cannons had was not shared with 20mm cannons other countries were producing - again no proof that cannon is a worse choice.

I was not complaining about the jamming sensitivity of the 20s. I was comparing six 50s to two 20s. With one gun jam, the six 50s only lose a sixth of its fire power, the 20s, however, lose half.

Wing clipping and rocket launchers were better choice than full-span wings of Corsair (would'nt fit in hangers) and no rockets at all. As for Malcolm hood, it took only one per plane (and not all the bird-cage Mustangs got it), unlike the cannons, that were 4 needed.

four 20s was indeed formidable.

 

[davparlr]

The RAF/FAA didn't rearm their US aircraft I agree probably for the same reason that the USAAF didn't, why should they it was good enough for the job that they had to do. Why go to all the trouble when the original was good enough and you need them ASAP?.

Exactly. The forces that had to make decisions did not feel replacing the 50 cals warranted the effort. They were doing the job.

I don't think the P51 used rocket in action but could be wrong, the Malcolm hood was needed as the original birdcage wasn't good enough and the F4U's had their wings clipped so they could fit inside the RN carriers whose hangers had less headroom than the USN carriers.

The point is that the British were not adverse to modifying US aircraft to meet some combat or operational need. I don't think they felt they had a need to replace the 50s.

 

[Shortround6]

I understand what you are saying but kinetic energy is also part of the energy equation and cannot be dismissed lightly.

No it can't but then the HE content should not be dismissed lightly either.

I said this poorly "replace the 50 in the Navy, whose tech staff did prefer it and did update after the war". I meant to say that the tech staff preferred upgrading the 50 to 20 mm and did update after the war.

The Navy was trying to update during the war, perhaps from the beginning of the war.

Oct. '44, some of the most vicious and deadly fighting using these "left over aircraft" was yet ahead for the allied forces in the Pacific, and the Navy was about to field the most powerful fighter it would field in the war, the F4U-4, with 50s.
With the F4U-4C it tried out the American gun, I think, and it was a failure. The Post war F4U-5 also came with 20mm, but I don't know which one.

There were 200 F4U-1C built with 20mm cannon, they did not see action until Okinawa. There were 300 F4U-4C built with 20mm canon post war. Some F4U-4E/N night fighters were fitted or retro fitted with 20mm guns. ALL F4U-5s were built with 20mm guns as were ALL later variants.

The problem here is when were the aircraft ORDERED vs when were they delivered and when did they see combat. The F4U-1C prototype first flies in August 1943 meaning that design work and metal cutting had to start earlier, Production doesn't start until July of 1944 and ends in Nov 1944, By the time the F4U-1C's see combat the F4U-4 has been in production for several months (perhaps over 5 months). First F4U-4 (with .50s) is delivered in Dec of 1944. The First F4U-4 combat victory is June 12 1945.

The navy could have easily decided in the Spring of 1944 to arm all "new" fighters with 20mm cannon. "New" meaning a fighter contracted for from that point on but not changing existing contracts. The Navy Issued a letter of intent for the F4U-4 prototypes in Jan of 1944. They ordered 300 of the "C" model with 20mm cannon on Jan 10th 1945, well before the -1Cs go into action or the F4U-4s with .50s. I don't know when the first 'production' contract for the F4U-4 was placed.

I have stated this before, from the Fall of 1944 it does not appear that ANY contracts were placed for Navy fighter planes of ANY type ( piston, jet, night fighter) that were not armed with 20mm cannon.

With over 23,000 20mm cannon on order (of the faster firing M3 type) in the spring of 1944 that is enough for 2875 four gun fighters with a complete set of 4 spare guns per fighter. What were they planning to do with these guns if they planned to keep the .50 as the standard gun?

 

[davparlr]

No it can't but then the HE content should not be dismissed lightly either.

I agree and I must admit that I lack any knowledge of impact of explosive shells.

The Navy was trying to update during the war, perhaps from the beginning of the war.

Maybe at BuAer, but I have not read anything about desire at ops, even at the Fighter Conference. Of course the Navy was fighting Japanese aircraft that were notoriously vulnerable to 50 cal fire.

I have stated this before, from the Fall of 1944 it does not appear that ANY contracts were placed for Navy fighter planes of ANY type ( piston, jet, night fighter) that were not armed with 20mm cannon.

I fully understand the Navy was moving toward the 20mm. However, to be picky, the FH-1 Phantom initial production contract was placed on 7 March, 1945, with four (!) 50 cals.

With over 23,000 20mm cannon on order (of the faster firing M3 type) in the spring of 1944 that is enough for 2875 four gun fighters with a complete set of 4 spare guns per fighter. What were they planning to do with these guns if they planned to keep the .50 as the standard gun?

I have never stated that the Navy did no plan to go to the 20mm, only that there was no urgency to do so because the weapons they had were effective. It is intuitively obvious that both the Navy and the AAF were interested in more firepower, aren't they always, but both apparently felt disrupting the prosecution of the war to upgrade their armament was counter productive. The Navy chose the 20 mm to upgrade firepower, the AAF the M3 50 cal. for their fighters. Both were effective through the Korean War. The post Korean War upgrades in rate of fire of the 20s made the next upgrade a mute point.

 

[Siegfried]

Please note that Charles Lindberg did shoot down several Japanese aircraft, that count for a gunnery and tactics expert. He was also an extremely good marksmen from childhood having to hunt for his food.

 

[tyrodtom]

Lindberg shot down one Japanese aircraft. When you read a account of the action, it was no great tactical feat. It was a Ki-51 Sonia, a army ground attack aircraft.