Armor Penetration - 20mm vs. .50 cal.

[Elvis]

HoHun,

You're "The Graph Guy", so make me a graph and show me something.

According to your stats, the 50 cal guns are firing approximately 13 rounds a second.
The 20mm is firing approximately 10 round a second.

Can you create a graph that shows the shot string of a 3 second burst from each gun?

I don't need to see it from a "number-of-guns" standpoint, one string from each caliber will be fine.

I want to see how much more, or less, "dense" each string is, given their rate of fire for a given period of time.





Elvis

 

[HoHun]

Hi Elvis,

Can you create a graph that shows the shot string of a 3 second burst from each gun?

Hm, here is a simple one:

.              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .
.                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .

12.7 mm upper row, 20 mm lower row

Regards,

Henning (HoHun)

 

[tomo pauk]

Hi, Sweb,

...
Regular incendiary begin burning in the barrel and quickly burned out the barrel. That's why they weren't used extensively. Many pilots preferred not to use them except as markers indicating they were low on ammo.
...

...
Incendiary rounds - tracers - were ignited when the round was fired so it began burning inside the gun barrel. They were white-hot and caused damage to the rifling of the barrel.
...

So the TRACER element burns, not the INCENDIARY element of the bullet. Just like I thought

As for damage to the barrel from "white hot" tracer, I don't think that was so. The real suff that could do the damage was burning propelant, mechanical thermical wear by moving bullet, humidity, salt for carrier A/C, inproper cleaning...

 

[delcyros]

Armor piercing rounds (API) did not burn in the barrel. They burned after piercing the target and they burned a magnesium composition that went instantaneously to a white-hot temperature that - simply stated - melted everything in close proximity to it. Magnesium, once ignited, cannot be extinguished. It burns itself out. One round lodged in an opponents spar will damage it to the point of failure. Tracers, on the other hand, because they burn of their weight on the way to the target have no striking power. If they penetrate they can do some serious damage but they weren't designed to penetrate. In WWI where wood and fabric were the bulk of construction materials the tracer was deadly. By WWII it was more of a "marker" round for gunners.

It´s quite difficult for any individual API round to be lodged into an spar rather than groing through. Also, the spar design itselve has quite an impact in whether it fails or not.
The chainsaw effect is also depending on the time exposure and density of rounds. High muzzle velocity will always tend to increase the mean distance between two successive projectiles, while low muzzle velocity tends to decrease distance between two successive projectiles.
On the point of impact for any given timeframe (whih is dependent on target sizes and exposure times) you want as close the distances as possible in order to maximize the chance of successive hits. In this way, lower velocity guns could have a surprising high density of fire, even at low rate of fire.

 

[Elvis]

Hi Elvis,

Can you create a graph that shows the shot string of a 3 second burst from each gun?

Hm, here is a simple one:

.              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .              .
.                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .                   .

12.7 mm upper row, 20 mm lower row

Regards,

Henning (HoHun)

Oh wow, cool chevron-esque pattern, when you hit quote!

Anyway, yep, just as a I thought.
Ok, thanks for making that "graph" for me.




Elvis

 

[Glider]

Its easy to get hung about about the numbers when sometimes it pays to stand back and look at the problem from a different point of view.

There is no doubt that the USA aircraft armed with 4 or 6 HMG's were more than sufficient for the task they had to face. They may not as been as efficient as a 20mm armed aircraft, but they were efficient enough for the task they had to do.

For the USN they had slightly different requirements compared to the USAAF. If a USAAF aircraft ran out of ammunition they could head for home, if home had been attacked and damaged it was pretty certain that they could divert or in a worst case scenario crash land or bail out over friendly territory. This is untenable for a USN aircraft, it has to carry on fighting. If 4 x HMG is good enough to do the job, then there are good reasons for the USN to accept 4 guns and more ammunition.

To critisise the Wildcat for not being equipped with 20mm from the start is being more than a little mean, 4 x HMG in late 1940 is above average for a single engined fighter. Certainly better than the 8 LMG on the RAF fighters, at least as good as the Me109 and by some margin better than those 109's only armed with 4 x LMG.

The ROF argument is also I believe exagerated. The 0.5 M2 fired about 13 RPSecond, the Hispano II 10 RPS. If you cannot hit someone with 10RPS, then you are still likely to miss them with 13RPS.

Instead of getting worked up over fractions of a MW here or there I find it easier to keep it simple. The USN compared the 0.5 to the Hispano 20mm and decided the 20mm was three times more effective, the USAAF did similar tests and decided that it was 2.5 times more effective. So a Hellcat, Kittyhawk or a P51D is about equal to Spitfire as the 4 x LMG often carried were of little use in Europe and ignored. If we are talking about the Pacific then I would give the edge to the Spitfire as the LMG's could do damage to the average Japanese aircraft.

 

[Demetrious]

"
Since you tried to evade the question of destruciveness with a hand-waving argument, let me remind you of the math... As P_hit_round, the probability of a hit for a single round, is not likely to be any worse for the Hispano cannon than for the 12.7 mm Browning...

You are comparing a four guns against two cannons, and trying to back it up with statistics that make a one-for-one comparison. The Browning M2 aircraft gun weighed roughly half what the Hispano cannon did, which makes your one-for-one comparison entirely fallacious, especially since you're trying to argue efficiency per pound.

Thus- any comparison made must compare an equivalent weight of armaments, which means roughly two Browning M2's versus one Hispano cannon. This answers your "rate of fire" complaint nicely: If the browning fired 13 rounds/second, then two Brownings were firing 26 rounds a second compared to the Hispano's 10.

That is an over-simplification, of course- "rate of fire" isn't the same as "pattern density," but they have somewhat similar consequences on accuracy. Either way, to claim that the probability of impact between an equivalent weight of cannon and machine gun favors the cannon is erroneous. More on this later.

You're way removed from reality ... the vast majority of kills were scored at short ranges where the trajectory curvature did not matter at all. And at long ranges, the out-of-centre mounting introduced aiming problems for wing-mounted armament that was more serious than trajectory curvature anyway. Rate-of-fire fallacy, see above.

You don't need to quote combat data at me to establish one of the most obvious truths of the war- most pilots were lousy shots, and most of them were trained to close to point-blank range before firing. That is obviously the optimal firing position, no matter if you have a feather duster or a laser beam to attack with. This also goes a long way towards forgiving the poor ballistics of many cannon, like the Japanese Ho-99 (which has remarkable raw efficiency, weighing slightly less then a Browning .50.)

Regardless, to say that cannon velocity is a moot point at standard combat ranges is foolish. Are you familiar with the problems of deflection shooting? Even at two hundred yards, the difference between the anemic ballistics of the Ho-99 cannon and the Hispano have a notable effect in how much lead one needs to pull. Even the difference of a few degrees of lead (when the deflection already demands X degrees) can be enough to put the target below an aircraft's nose, and out of sight, making the shot difficult, if not outright untenable.

There are other advantages, such as being able to hammer bombers from safely outside effective defensive gun range, but the lead issue in deflection shooting is the most poignant.

Of the 272 "destroyed" claims resulting from these 482 combats, 86 % were from combat distances of 400 yards or less.

400 yards is long-range, for air-to-air gunnery against fighters. Extremely long range, at that. Against a manuvering target, 300 is pretty much the max range any decent shot could expect to score at. 200 yards can still be a tricky shot, especially against a manuvering target in a deflection shooting scenario.

My experience is not scientific, but having played an excessive amount of reasonably accurate simulation games (and having been able to sample a broad array of different modeling approaches,) generally I have found that the differences in gun ballistics are still felt very, very much in deflection shooing even at two-hundred yards. And that's just in a game. In real life the difficulty is greater by a few orders of magnitude.

Note that from switching to Hispano cannon, you get a 20% firepower increase coupled with a 27 kg weight reduction and an ammunition supply increase, both expressed in duration of fire and in total energy, by more than a factor of two.

Where are you getting your weight data? I got mine from here: linky. That data only shows a 16kg advantage for the Hispanos (assuming the earlier model Hispano, which is what we seem to be discussing.) EDIT: Disregard that, I looked at the wrong column when I wrote that.

Now, as for "pattern density." This is fancy talk for the fact that for roughly equivalent weight, you have two machine guns firing for every one cannon. I hesitate to equate this with "rate of fire," because ROF describes the density of the bullet "stream," not the pattern of hits it effects upon the target, but nonetheless the machine guns put more then twice the number of projectiles in the air. Due to gun vibration and other factors, this pattern is spread out a bit, though not enough to be terribly problematic at standard combat ranges.

Assuming a decent pilot firing in deflection at two-hundred yards, this means a random clustering of hits around the fuselage. Even two-hundred yards in a deflection shot is a bit long to allow for precise aiming (such as targeting the wing root,) and since the planar view allowed by deflection allows access to the pilot and engine anyway, we'll assume a random clustering of hits on the fuselage. Clearly, with twice the amount of projectiles in the air, the M2 Brownings have twice the chance of scoring on a vital area, such as the engine, or the cockpit. (Also recall that even at shorter ranges, most shots will still result in a pattern bigger then the target. Even zero-deflection shots from the cold six in gun camera film shows half the burst missing, due to the lower target profile.)

Conversely, of course, cannon shells make for dynamic and exciting explosions no matter where they hit. A 20mm cannon strike in the center of the wing will do damage that effects aerodynamics, whereas a .50 will not. This goes some way towards forgiving the lower pattern density of cannons, obviously. On the other hand, I question just how effective cannon strikes on non-vital areas are. A hole punched in a wing will affect aerodynamics and performance, certainly, but it still will not take a plane out of the fight like one or two .50 rounds in the engine block will. (This is a bullet the size of your thumb, after all.)

Additionally, there is the question of the statistical probability of delivering a sufficient amount of damage to a vital area. What constitutes a sufficient amount of destructive power, to a vital area? Clearly raw megajoules might not be the proper measure here (I'd rather have three .50 API rounds punch into the bowels of a liquid-cooled engine rather then a single 20mm hit which would expend half of it's explosive force on the cowling in the wrong direction- assuming a non-shaped charge, which I think they were.) Even if the cannon could deliver more destructive force to the vital area, it is a vital area- it might be more important to simply land a hit there in the first place, rather then deliver superior energy haphazardly.

Now we have a lot of factors to consider. How wide or tight is the pattern, (assuming two guns to equate one cannon?) How many .50 BMG strikes does it take in a vital area to score lethal damage? One? Two? Five, Ten? If it's too high, the .50 still loses. What exactly is the effectiveness of cannon strikes on non-vital areas? How does this vary with caliber? (A 20mm hole in the wing is annoying, but a 30mm may just amputate it.) Does the raw megajoule rating of the chemical explosive in cannon shells accurately reflect actual energy delivered to target, given the nature of unshaped explosives? Given that explosive cannon shells had roughly the same amount of armor penetration as AP .50 cal, does that mean .50 cal was more effective because it was twice as likely to score a hit on a vital area, and yet just as likely as the cannon shell to penetrate and wreak mayhem? Does a .50 cal round retain more energy after breaching amour then raw chemical explosives, or does the superior amount of energy in the cannon shell more then compensate for it? Even if the .50 caliber guns prove more effective at landing sufficient damage in vital areas, does the greater ammunition efficiency of the cannon make up the difference in hit probability by virtue of extended firing duration? How does the characteristics of various aircraft effect this, given that some were much better gun platforms then others?

Try writing me a function that can calculate that. Do it in Lisp for extra points.

The myriad factors at play here are why I am still undecided on the question of cannons. I will note here that the Hispano is not representative of most WWII fighter cannon- it had both a good rate of fire, low weight, AND excellent ballistics, while most cannons of the war could claim at most one, perhaps two, of those traits. The chart from Mission4Today is a nice reference for weight and ROF, but most of what I know of their ballistic traits has been learned from extensive reading, some of it being pilots accounts (and therefore not easily referenced.) The .50M2's good rate of fire and reliable ballistic performance made it competitive against most WWII cannons. The Hispano, of course, is another story.

 

[tomo pauk]

For extra fun: how do you folks rate effectivenes of 37mm cannons ( the US M4 and Russian NS-37 ) for air combat?

 

[HoHun]

Hi Demetrious,

>You are comparing a four guns against two cannons, and trying to back it up with statistics that make a one-for-one comparison.

Hm, I think you should have given me some hint on how you arrived at this idea, but as far as I can tell it's completely wrong.

Here is the weight data I am using:

Hispano II: 50 kg for each gun, 246 g for each cartridge
12.7 mm Browning: 29 kg for each gun, 136 g for each cartridge

Firepower per barrel:

Hispano II: 1.06 MW
12.7 mm Browning: 0.28 MW

Thus this firepower comparison:

2 x Hispano II: 2 * 1.06 MW = 2.12 MW
6 x 12.7 Browning: 6 * 0.28 MW = 1.68 MW
4 x 12.7 Browning: 4 * 0.28 MW = 1.12 MW

And the weight comparison:

2 x Hispano II at 472 rpg: 2 * (50 kg + 472 * 246 g) = 332.2 kg
6 x 12.7 Browning at 240 rpg: 6 * (29 kg + 240 * 136 g) = 369.8 kg
4 x 12.7 Browning at 180 rpg: 4 * (29 kg + 430 * 136 g) = 349.9 kg

(Note: These weights for the Browning batteries are slightly higher than those I posted above because I erroneously used 110 g per cartridge until recently. However, this is an error in favour of the Browning.)

I'd like to hear a good explanation from you how why you thought you could accuse me of blundering as badly as you claimed I did, and I'm disregarding the rest of your post for now ...

Regards,

Henning (HoHun)

 

[davparlr]

Hi Davparlr,

Of course it was a failure, considering that it gave them the same firepower and ammunition supply they could have had from two Hispano canon while saving more than 200 kg of weight.

This is an interesting application of logic. We won the game but our defense was a failure? Nothing fails like success? The 50 cal round was immensely effective in the counter air role with thousands of enemy aircraft erased from the sky. I guess that, using your logic, the use of the German Mauser was a failure because it had less firepower than the M-1, the Mark IV tank was a failure because it didn't have the gun the T-34 had, the T-34 was a failure because it didn't have the gun of the Tiger. Is any weapon system not a failure? There is far more to a successful design that just firepower.

The arguments for the 50 cal is as follows:

1) Economy of scale. The 50 cal was, and is, an amazingly versatile weapon, used by infantry, armor vehicles, ships, naval aircraft, bombers, and fighters. Hugh amounts were produced along with ammunition.
2) Reliability. Long operation generated a very reliable weapon. US Hispano 20s seemed to have reliability problems. They were tested on F4U-1Cs and were not liked.
3) Production line incorporated the 50 cal, implementing the 20 mm would interrupt the line. Allied philosophy emphasized hordes of "sufficient" weapons, vs. the German approach of a limited high tech weapons. In engineering, the comment by the program management is "better, is the enemy of good enough", implying that the pursuit of better prevents the fielding of systems in a timely manner.
4) Battlefield reports. Reports from warfighters reflected no concern about the effectiveness of the 50 cal, thus no pressure to make the change.

As I already pointed out, they had no comparison. And I have not seen any comments that show that they were aware of the weight penalties they were paying for their overweight guns

They may have not have known what they were missing, but they were quite aware of what worked.

Due to weight, and also due to duration of fire. However, if you look at the details, you'll find that it would have been possible to give the F4F-4 (guess your "-5" was only a type) a cannon battery that weighed no more than that of the F4F-3 while at the same time increasing firepower and duration of fire beyond that of either type ... simply by using cannon.

This does indicate that there was little concern about the effectiveness of the 50 cal. The -5 error was not a typo but a mental error. I had been working with data on the F6F and got it confused with the F4F.

What would these cannon have done for the US navy?

- They would have increased firepower by a factor of almost 2 over the F4F-3 battery (at the same weight).
- They would have increased the total firing duration by a factor of 1.3 over the F4F-3 battery (at the same weight).
- They would have increased the total ammunition supply by a factor of 2.4 over the F4F-3 (at the same weight).
- It would have increased firepower by more than 20% over the six-gun battery of the F4F-4 (at lower weight).

Probably not much. There is report after report that says the Japanese aircraft flamed with one burst. Rifle caliber would probably have worked fine.

There is an inefficiency of overkill. One can blow up a watermelon with a 50 cal sniper rifle or a 22 cal M-16. Fighter planes tend to be more fragile than bombers. You have never supported you argument with data showing effectiveness of 20 mm over 50 cal against targets. If the target is a watermelon, there would be no difference. If it was against a B-29, it probably would be significant. Most fighters would be much tougher than a watermelon, but not near as tough as a B-29. I would guess that a two second burst of four 50 cals would be close to 100% of the effectiveness of a two second burst of two 20 mm against the fuselage of a Zero. Would two 20 mm rounds into a radial be any more effective that four 50 cals? Probably not, both would do the job. What data is really needed is the number of kills verses weight thrown or, maybe more important, number of kills per seconds fired.. This is probably not available.

So, if I was a weapons program manager circa 1944, and bright lieutenant came into my office and provided me this argument, this is what I would weigh.

I have multiple production lines producing about 6300 fighters a month.

I have a recommendation to change armament from 50 cal to 20 mm because of higher energy contained in the 20 mm should be more effective on airborne targets.

Actual performance efficiency advantage against expected threat is unknown, e.g., improvement in actual kills in combat is undefined.

I would have to redesign and engineer multiple platforms to incorporate the 20 mm cannon. This would require stronger structure to handle recoil and larger ammo storage bin (offset by reduction in number). Cost of updates, unknown, and risk, minor.

Production lines would have to be interrupted to incorporate engineering changes, cost impact is major and schedule impact is minor to moderate.

We would need to make decision on retrofit.

If no retrofits, parallel logistics, including spares and training, required. No aircraft down time required. Weapon logistics and maintenance effort will be almost double present effort.

If retrofit required, prepare retrofit kits for delivered aircraft. Aircraft will require down time for removal of 50 cals and installation of retrofit kits. Down time is unknown, impact to operations, minor to moderate.

Major new weapons manufacturing facilities required, capacity 13,000 20 mm cannons per month. Cost impact, high, schedule impact high.

Expansion of 20 mm aircraft ammunition manufacturing, which may require facilities upgrade, will be required. Reduction will also be required in 50 cal output.

There is a reliability issue on U.S. manufacture of 20 mm cannon. Corrective action unknown, but will impact fielding of weapon.

Is the request from operations? No, war fighter is happy with the effectiveness of 50 cals.

So, Lieutenant Henning, you want me to build brand new large manufacturing facilities, either start an expensive retrofit program or double my logistic train, lose operational readiness, lose standardization, and spend loads of money, money I could use to build more aircraft, based solely on your analysis of energy per round, without providing any supporting data on how sorties per kill are improved or how the time delay and cost of this improvement will be made up by efficiency. In addition, there was no request from the war fighter for this upgrade, therefore, no apparent need.

So, with this data, my answer is, no. However, Lt. Henning, I do have a weapons support position open in the Aleutians that I think you may enjoy.

You can excuse any type of inferior Allied equipment that way since it was still "sufficient to win the war". That really doesn't mean anything.

When "sufficient to win the war" means enough equipment can be manufactured to efficiently end the war quickly, it means a lot. The M-26 was a much better tank than the M-4, but, could much fewer M-26s have ended the war quicker? Probably not. Therefore saying the M-4 was "sufficient to win the war" was an important statement that the Germans never seemed to grasp.

 

[mad_max]

This horse has been beaten so many times on so many boards that it's redundant.

Bottom line is:

1. Ma Duce did the job the USA needed at the time. Even better with API
developed. Although it took banks of guns to be very effective and we
had the aircraft to carry them.

2. Logistics demand was less since only .50's needed for all aircraft, plus
use on other equipment.

3. No retooling/renovating equipment for 20mm. No stoppage of supply.

4. Our 20mm had problems at the time and the Ma Duce was reliable. Only
logical to use the Ma Duce.

See easy wasn't it? 8)

 

[HoHun]

Hi Davparlr,

>This is an interesting application of logic. We won the game but our defense was a failure?

Here is my original quote: "Post-war popular book talk rationalizing the USAAF's failure to employ cannon, if you ask me."

Of course you can make serious mistakes and still win a game. Sticking to machine guns was a serious mistake, and if you read Admiral King's telegram, you'll realize that the Navy believed that insufficient armament (and poor fighter performance) almost made them lose the Battle of Midway.

>The arguments for the 50 cal is as follows:

>1) Economy of scale. The 50 cal was, and is, an amazingly versatile weapon, used by infantry, armor vehicles, ships, naval aircraft, bombers, and fighters. Hugh amounts were produced along with ammunition.

Do you actually have a price tag for the 12.7 mm Browning vs. the 20 mm Hispano, or are you just making this up? Considering that three 12.7 mm machine guns were needed to replace one cannon, I'd be surprised if it actually was economic at all.

>2) Reliability. Long operation generated a very reliable weapon. US Hispano 20s seemed to have reliability problems. They were tested on F4U-1Cs and were not liked.

The lack of reliability of the US Hispano was home-made and avaoidable, and just demonstrates another mistake in US armament development:

Modifications and Attempts at Standardization

>3) Production line incorporated the 50 cal, implementing the 20 mm would interrupt the line.

That is not a strength of the 12.7 mm Browning, but another failure in US procurement planning. The British with their much narrower industrial base seem to have had few problems to supply enough cannon for the RAF ...

>4) Battlefield reports. Reports from warfighters reflected no concern about the effectiveness of the 50 cal, thus no pressure to make the change.

Admiral King's telegram included a rather serious complaint about armament, and my comparison which showed the great margin of superiority the Hispano enjoyed over the Browning shows that effectiveness is only a small part of the equation since fighter performance is greatly affected by weight. The Brownings were moderately effective but extremely heavy and thus induced a performance penalty for any aircraft they were installed in.

>This does indicate that there was little concern about the effectiveness of the 50 cal.

Actually, I'm surprised that you evade the obvious: Admiral King's telegram shows intense concern about the quality of the entire weapons system. King's specific demands were:

- Reduce the weight of the F4F-4.
- Increase the ammunition supply.

Here are the options:

6 x 12.7 Browning at 240 rpg: 6 * (29 kg + 240 * 136 g) = 369.8 kg (31.4 MJ total supply)
4 x 12.7 Browning at 180 rpg: 4 * (29 kg + 430 * 136 g) = 349.9 kg (37.5 MJ total supply)
2 x Hispano II at 236 rpg: 2 * (50 kg + 250 * 246 g) = 223.0 kg (53.1 MJ total supply) <- example battery

The Hispano II example battery addresses both issues Kind raises with the F4F-4 and its armament by increasing the ammunition supply by 40% and saving about 324 lbs of weight at the same time. It also increases firepower.

>So, if I was a weapons program manager circa 1944 [...]

The Battle of Midway occurred in 1942. At least try to stay honest, and cut the condescending "Lieutenant Henning" crap.

The mistakes in US weapons procurement were made long before 1944, and in fact before 1942 as well. To understand the timeline requirements, just look at the history of the Hispano's introduction in Britain - or at the introduction of the MG 151/20 in Germany to see a new design introduced successfully in wartime.

The the Allies won the war does not mean that they didn't make any mistakes in weapons procurement, and the heavy weight of the 12.7 mm machine gun and its ammunition seriously hampered US fighters and bombers in all aspects of their performance.

Regards,

Henning (HoHun)

 

[HoHun]

Hi Madmax,

>2. Logistics demand was less since only .50's needed for all aircraft, plus
use on other equipment.

Since your other points were redundant to Davparlr's, consider them addressed there.

With regard to the logistics demands: If you look at the complexity of keeping a squadron of aircraft supplied with a large number of highly-specific spare parts, the provision of a small number of standard high-turnover parts is a trivial job that does not justify carrying several hundred pounds of extra weight on each fighter just for sake of standardization with army ground units.

Regards,

Henning (HoHun)

 

[Clay_Allison]

I still think that a compromise was the best route. Neck up the .50 to .75 and develop a meaningful HE projectile, more ammunition selection in general. The gun stays the same with a different barrel, the production lines are uninterrupted, the planes are unaltered, it's all win.

 

[HoHun]

Hi Davparlr,

>You have never supported you argument with data showing effectiveness of 20 mm over 50 cal against targets.

You could start here for a study of destructiveness:

WORLD WAR 2 FIGHTER GUN EFFECTIVENESS

Regarding the 12.7 mm Browning vs. 20 mm Hispano, the case is particularly simple as the US Navy itself assumed a 1:3 firepower relation (as Tony points out).

If you have any data that doesn't agree, I'd like to see it ...

Regards,

Henning (HoHun)

 

[Glider]

Hi Davparlr,

>You have never supported you argument with data showing effectiveness of 20 mm over 50 cal against targets.

You could start here for a study of destructiveness:

WORLD WAR 2 FIGHTER GUN EFFECTIVENESS

Regarding the 12.7 mm Browning vs. 20 mm Hispano, the case is particularly simple as the US Navy itself assumed a 1:3 firepower relation (as Tony points out).

If you have any data that doesn't agree, I'd like to see it ...

Regards,

Henning (HoHun)

Henning

Here is one of the anomalies in the figures you have prepared.

You are of course correct that the USN did estimate 1:3 firepower relation and other members of this forum have stated that the USAAF did a similar assesment and came up with a 1:2.5 relationship.

If I read them right, your figures give close to a 1:4 relationship. I find it difficult to believe that the USN and USAAF would be between 35-55% out in their findings.

I do not doubt or wish to diminish the effort that you have put into this topic which is significant and a lot of the logic that you use makes sense, but I cannot help felling that something is missing. I don't pretend to know what it is possibly an underestimation of the importance of MV or an exageration of the extra chemical energy.

PS in the examples flying around I think there is a typo in the calculation for the 4 x HMG.

 

[Colin1]

Neck up the .50 to .75 and develop a meaningful HE projectile

The gun stays the same with a different barrel

Doesn't that, by definition, make it a cannon now?

Does it, though? Would the weapon still be capable of disgorging a .75 casing from a breech designed for .50 without any risk of a stoppage? The weapon has now stepped up to 19mm or thereabouts, surely the performance and/or ballistic characteristics of the weapon would change significantly? I don't know myself, I'm just asking

 

[tomo pauk]

Re. necking up the BMG:

Since the casing base and length would remain the same if we 'straight the neck', the ammo load and ejection mechanisms would have no problems.
The sucessfull examples of necking up were the German MG-151 to MG-151/20 (15 mm-> 20mm) and Russian UB to B-20 (12,7mm -> 20mm).

Since the resulting caliber would be indeed around 18mm, it would be worthwile to manufacture the exploding shell for it, so making it cannon.

 

[Clay_Allison]

Doesn't that, by definition, make it a cannon now?

Does it, though? Would the weapon still be capable of disgorging a .75 casing from a breech designed for .50 without any risk of a stoppage? The weapon has now stepped up to 19mm or thereabouts, surely the performance and/or ballistic characteristics of the weapon would change significantly? I don't know myself, I'm just asking

Ok, this is my wheelhouse, as I know way more about guns than planes. The cartridge case would be the same, but the neck (where the bullet goes) would be enlarged to .75, making a cartridge that would have all of the same dimensions as far as the internals of the gun are concerned. All you would need to do to convert an existing .50 to .75 BMG is replace the barrel.

Read up on "Wildcat" cartridges and you'll find that this has been done with every major rifle cartridge in history by sportsmen.

Yes, it would be a light cannon, more like the Japanese 20mm than the H.S.404.

As for trajectory and performance, I'm not an expert on WWII powders, but I know modern magnum velocities were unattainable and just about every cartridge on the planet had a ~2800 fps speed limit. The only cartridge in the world that had broken 3000 is the 250 savage (.25 caliber varmint cartridge). Whenever you hit these limits it becomes easier to throw a heavy bullet than it is to make the bullet go faster.

The .50 BMG is a fantastic cartridge case, lots of inherent strength, lots of powder capacity, long for its diameter so well suited to developing pressure smoothly and moving heavier projectiles. It is a scaled up 30-06, and that says a lot considering the universality of both the .50 and the 30-06 in the free world. I believe that in 1940, it certainly had untapped potential. I think that going up to a 1000 grain projectile for the AP (the heaviest projectile you'll throw) would only slow the MV slightly, maybe to the 2650 range, not enough difference to make shooting harder.

 

[Colin1]

...The cartridge case would be the same, but the neck (where the bullet goes) would be enlarged to .75, making a cartridge that would have all of the same dimensions as far as the internals of the gun are concerned. All you would need to do to convert an existing .50 to .75 BMG is replace the barrel...

All good
I twigged it from tomo's post, it's the warhead that would change diameter not the casing, hence the need for a new barrel