20mm cannon, best, worst, specs, comparison to LMG, HMG etc.

[claidemore]

20mm cannon...was it the WWII air to air weapon of choice?
How did it compare to LMGs, HMGs, 15mm cannon, 30mm, 37mm?
How did the various 20mm weapons compare, and how did their various ammo types perform?

Any thoughts or opinions?

Or we could all just own up to the fact that the Hispano was the be all and end all of 20mm cannon and be done with it!

claidemore

 

[Jabberwocky]

Start with these articles from Tony Williams

Cannons vs MG:

CANNON OR MACHINE GUN


WW2 gun effectiveness

WORLD WAR 2 FIGHTER GUN EFFECTIVENESS

Ideal WW2 fighter armament

IDEAL WW2 FIGHTER ARMAMENT

Assessment of armament of BoB fighters

THE BATTLE OF BRITAIN

Hispano in US service

Modifications and Attempts at Standardization


Also, Tony's co-conspirator, Emmanuel Gustin has similar web pages:

Gun effectiveness

The WWII Fighter Gun Debate: Gun Tables

Fighter armament comparisons

The WWII Fighter Gun Debate: The Fighters

Analysis of armament positioning and choices

The WWII Fighter Gun Debate: Analysis

Weight of fire assessment

Fighter Gun Table


Also, aircraft gun ballistics tables

Lunatic's WWII Aircraft Gun Ballistics Page


THEN come to a considered answer.

For my money, the best all-rounder would be the Berezin B-20, followed by the Mk V Hispano. Anything heavier and the MK 108 is head and shoulders above the rest.

 

[fastmongrel]

Thanks for those links Jabberwocky lots to read and absorb. First impression is how good the Soviet guns were.

 

[Shortround6]

Thanks for putting all those links in one spot Jabberwocky.

I would add that ammo changed during the war and that affected the performance of guns at various times.

 

[Tante Ju]

Best gun (only gun). Soviet B-20 cannon. Very light, great ballistic, great cyclic rate. Like Mauser cannon, developed from actually heavy caliber machine gun Berezhin..

However if best gun is considered with ammunition, best gun is Mauser 151. Rate of fire, velocity - almost similiar to Berezhin 20, but heavier. However, German Mine shell was better than Soviet shell, or British shell. Both latter are only fraction of explosive capacity because they are drilled, Mauser is drawn type shell. More space. British shell, early type also had serious problems.. bad fuse, very bad. Sometimes explodes in own aircraft near, but on only skin of enemy aircraft, making less damage than possible if explosive in structure occurs.. So hit from Mauser was many times destructive than these.

Hispano - not very suited. Was fine for French designs - single gun, no problem with weight. But too big for what it knows to do. Later shorter, lighter Mark V reflects this, this was good gun, like Mauser, but too late, only on few Haweker Tempest fighter used.

Japanese - copy of Oerlikon, German guns. Total chaos really.. but the 40mm version was very innovative solution. Perhaps best large calibre practical gun.

Also great advantage when syncronized in installation, is electric firing method - no loss - and pneumatic re-charge capacity. Latter was possible on Soviet gun too. Useful if jam.

Best heavy calibre gun - Berezhin UB 12,7mm. Far best. Light, powerful, fast firing. US even copied its incendinary ammo for Browning model heavy calibre machine gun.

 

[Shortround6]

See my previous post. The Hispano fuse problem was sorted out fairly soon and was certainly not a problem for the entire war. In fact it may have been fixed by the time the MG 151/20 was in wide spread service. Hispano API could penetrate the same amount of armor as a US.50 cal AP round but carried 10 grams of HE/incendiary filler behind the plate.

The Japanese 40mm was actually a terrible gun. with a MV half of MK108 it was ultimate "you have to get close' gun. rate of fire was slow and the "Projectile" weight includes the powder chamber if not the propellant giving a rather exaggerated idea of it's hitting power.

Picture of ammo: http://www.thegunwiki.org/wiki/imag...jectile.jpg/300px-Ho-301_40_mm_projectile.jpg

 

[Glider]

The BR 20 was a remarkable weapon without doubt but it was a late war weapon and only carried by some of the LA7 where it was syncronised. The comment re the Hispano II is a little harsh. It was heavy but not that much heavier than the 20mm Mg151 and still very effective but like you the nod goes to the Mg151 with its mine shell.

 

[davebender]

The gun and ammunition constitute a weapons system. IMO they must be considered together.

The MG151/20 cannon remained in production in one form or another into the 1970s. How many other WWII era 20mm cannons have that sort of record?

 

[Tante Ju]

See my previous post. The Hispano fuse problem was sorted out fairly soon and was certainly not a problem for the entire war. In fact it may have been fixed by the time the MG 151/20 was in wide spread service.

I read that problem still exists in July 1942. HE round auto-detonate at barrel and damage gun, other get great spread because fault design of driving head. 16 out of 250 round fired effected so, so fairly common.
API rounds good reported, AP two piece design very bad, breaks up in bomber fuselage.. Also API (SAPI) was ineffective causing fires in fuel tanks unless they are armored (were not in German bomber.. were in 109 though) to activate round. doesn't look like 'fixed' and MG 151/20 was introduced a whole year before that report of Hispano rounds..

Hispano API could penetrate the same amount of armor as a US.50 cal AP round but carried 10 grams of HE/incendiary filler behind the plate.

No, I think you mix up Hispano API round with HE round.. it would be funny if near-solid API would carry so much.

It doesnt work this way, you cannot have properties of API round and HEI round at same time... API round could penetrate armor, but had no explosive; HEI round could not penetrate any significant armor. You want both.. Test show HEIT type could penetrate less than 4 mm, as it detonated in the fuselage before attack armor; HEI type about 8 mm.

And no Hispano round carried 10 grams of HE/incendiary filler. Sorry I think this is wrong. Do you have cut diagram of round perhaps in British RAF. US HEI: they carry 5 gram of total, half-half of 2.5 gram: explosive, 2.5 gram incendiary. I think same as RAF. It would be funny if solid API round carry twice as much as special HE rounds of Hispano...

The Japanese 40mm was actually a terrible gun. with a MV half of MK108 it was ultimate "you have to get close' gun. rate of fire was slow and the "Projectile" weight includes the powder chamber if not the propellant giving a rather exaggerated idea of it's hitting power.

I would not call it terrible; it is very light, and gets great punch. The shell carried 65 gramm explosive - say 12 times Hispano round. It like shotgun, but I agree, for a little plus weight, MK 108 is much more practical. Shell 20% more power, MV twice, cyclic rate bigger etc. Greatest advantage is that Ho 301 is limited to 10-round "clips" - MK 108 can can carry as many there is place for.. I think about 135 round per gun was maximum, on Bf 110G. Still I think Ho 301 is very innovative gun, caseless etc.

The BR 20 was a remarkable weapon without doubt but it was a late war weapon and only carried by some of the LA7 where it was syncronised. The comment re the Hispano II is a little harsh. It was heavy but not that much heavier than the 20mm Mg151 and still very effective but like you the nod goes to the Mg151 with its mine shell.

Hi Glider!

I think we can judge firepower aspects

1 weapon as installed, like BR 20 in La 7
2, Weapon as self
3, Weapon as complex system of ammunition and possibilities for installment. Like: possible to install synronized? In wing? Through cannon shaft?

I agree about what you say is BR 20 late war. Late war of course always better - almost - because experience of early war. But I think my insight is analytical, like in No. 3 point. All things consider, possibilities. Good qualities: low weight, high ballistics, high cycle rate, misc. like reliability etc. You are right as you address "BR 20 in La 7" which is point 1, but I think of Point 3 more. So we speak little different when talk of same subject.

Ammo question I was unsure. Surely Mauser is very good design. Light, slim, compact, few pieces so easy to maintain. Big plus is however - Mine shells. If we approach from Point 2 - gun itself - it can not escape conclusion that say Shwak could fire Mine shell, had it developed. Hispano too. Or least, very likely. So, if we concentrate on "How good design of gun itself really was"?, ammo can be put aside. To create playing field that is even. Of course life was not. But for analytics this can be useful.

I do not have doubt of Hispano was very effective. It worked well. In my idea however, such qualities gun is best choice when there is only one, like French fighter moteur cannon. I think for ideal air weapon, lighter, more compact is better solution overall - say gain is obvious, when same weapon weight, you could have 3 Mark V Hispano instead of 2 Mark II Hispano and you fire 2 times the bullet because weapon also fires faster. Or you can say Mauser or Shwak. Mark V shows in my opinion British were thinking same, sacrificed bit of ballistics, but ballistic property is not so much important for air gun in opinion of mine (and people designed above guns - fire on aircraft, only 2-300 meter distance typical. Further, hit probability is so low, even with best external ballistics gun, not worth trying..

 

[davebender]

Good weapon. Wrong use. I think the Ho-301 cannon would have made a fine weapon for the Imperial Japanese Army. Just need a decent tripod mount.

Ho-301 Cannon.
108 lbs. Weapon weight.
805 fps. Muzzle velocity.
475 rpm. Cyclic rate.
.59 kg. Projectile weight.


Mk19 Grenade Launcher.
72.56 lbs. Weapon weight (without tripod)
790 fps. Muzzle velocity.
325 to 375 rpm. Cyclic rate.

 

[Shortround6]

I read that problem still exists in July 1942. HE round auto-detonate at barrel and damage gun, other get great spread because fault design of driving head. 16 out of 250 round fired effected so, so fairly common.
API rounds good reported, AP two piece design very bad, breaks up in bomber fuselage.. Also API (SAPI) was ineffective causing fires in fuel tanks unless they are armored (were not in German bomber.. were in 109 though) to activate round. doesn't look like 'fixed' and MG 151/20 was introduced a whole year before that report of Hispano rounds..

less sensitive No 253 fuse introduced in 1941, it may have taken a while to replace most older ammo. My mistake on the API, it was a SAPI, an AP nose cap fitted to a standard incendiary shell body. it carried 10 times what the US .50cal API did not 10 grams but that should still put it at 8 grams or better. Since a 20mm Hispano could penetrate a lot more armor than a .50 cal sacrificing some armor penetration for payload wasn't that much of a sacrifice.

No, I think you mix up Hispano API round with HE round.. it would be funny if near-solid API would carry so much.

see above.

It doesnt work this way, you cannot have properties of API round and HEI round at same time... API round could penetrate armor, but had no explosive; HEI round could not penetrate any significant armor. You want both.. Test show HEIT type could penetrate less than 4 mm, as it detonated in the fuselage before attack armor; HEI type about 8 mm.

Yes, you can have both. You just need a big enough shell and enough velocity. Hispano shells weighed 128-130 grams. German non-mine shells weighed 115-117 grams(?) and had much lower velocity. The problem is getting the fuse to function as wanted and nobody's fuse was 100% or even close to it. German mine shells didn't have a body strong enough to penetrate much armor. In one British test they found that 12mm face hardened armor would offer protection from German 20mm HEI shells with quick action fuses. 6.6mm of homogeneous armor would offer the same protection. A British 20mm Hispano shell MK I.z HE, was expected to blow a hole 75mm to 200mm across in 12mm armor (type not stated). while the shell doesn't technical penetrate whatever was on the the other side of the armor would be in poor condition.

And no Hispano round carried 10 grams of HE/incendiary filler. Sorry I think this is wrong. Do you have cut diagram of round perhaps in British RAF. US HEI: they carry 5 gram of total, half-half of 2.5 gram: explosive, 2.5 gram incendiary. I think same as RAF. It would be funny if solid API round carry twice as much as special HE rounds of Hispano...

Argue with Tony Williams, one of his books lists 10.5 grams of Pentolite or 10.2 grams of Tetryl in the MK I.z and 7grams Tetryl + 4.3 grams incendiary in the MK 1 US HEI. Granted the percentage of weight devoted to explosive is under 10% but those heavy shells push the results over 10 grams.

By the way an API cannot be solid just by definition. An AP round can be, but an API is armor piercing incendiary which means there has to e some incendiary somewhere in the projectile, therefor it is not solid.

I would not call it terrible; it is very light, and gets great punch. The shell carried 65 gramm explosive - say 12 times Hispano round. It like shotgun, but I agree, for a little plus weight, MK 108 is much more practical. Shell 20% more power, MV twice, cyclic rate bigger etc. Greatest advantage is that Ho 301 is limited to 10-round "clips" - MK 108 can can carry as many there is place for.. I think about 135 round per gun was maximum, on Bf 110G. Still I think Ho 301 is very innovative gun, caseless etc.

It may have been innovative but it was also near useless as an air to air weapon. The velocity is about that of a .45ACP pistol round. Whatever complaints people had with the MK 108 are doubled for the Ho 301. The low velocity means times of flight even a short ranges are double the MK 108s and the curved trajectory (exaggerated by some critics of the MK 108 ) is all to real for the Ho 301.
The Japanese may have been able to hit a few bombers with it but I don't think it was a viable air to air weapon. Some potential as a barge or small boat straffer perhaps.

 

[Glider]

Hi Glider!

I think we can judge firepower aspects

1 weapon as installed, like BR 20 in La 7
2, Weapon as self
3, Weapon as complex system of ammunition and possibilities for installment. Like: possible to install synronized? In wing? Through cannon shaft?

I agree about what you say is BR 20 late war. Late war of course always better - almost - because experience of early war. But I think my insight is analytical, like in No. 3 point. All things consider, possibilities. Good qualities: low weight, high ballistics, high cycle rate, misc. like reliability etc. You are right as you address "BR 20 in La 7" which is point 1, but I think of Point 3 more. So we speak little different when talk of same subject.

Ammo question I was unsure. Surely Mauser is very good design. Light, slim, compact, few pieces so easy to maintain. Big plus is however - Mine shells. If we approach from Point 2 - gun itself - it can not escape conclusion that say Shwak could fire Mine shell, had it developed. Hispano too. Or least, very likely. So, if we concentrate on "How good design of gun itself really was"?, ammo can be put aside. To create playing field that is even. Of course life was not. But for analytics this can be useful.

I do not have doubt of Hispano was very effective. It worked well. In my idea however, such qualities gun is best choice when there is only one, like French fighter moteur cannon. I think for ideal air weapon, lighter, more compact is better solution overall - say gain is obvious, when same weapon weight, you could have 3 Mark V Hispano instead of 2 Mark II Hispano and you fire 2 times the bullet because weapon also fires faster. Or you can say Mauser or Shwak. Mark V shows in my opinion British were thinking same, sacrificed bit of ballistics, but ballistic property is not so much important for air gun in opinion of mine (and people designed above guns - fire on aircraft, only 2-300 meter distance typical. Further, hit probability is so low, even with best external ballistics gun, not worth trying..

I don't quite get your comment 3 but the Hispano II as you say was pretty effective. Interesting point about the Hispano II and V and that they were interchangable, the mounts wre the same so in theory any RAF fighter could use them. In reality they were assigned to the Tempest.

 

[Greyman]

And no Hispano round carried 10 grams of HE/incendiary filler. Sorry I think this is wrong. Do you have cut diagram of round perhaps in British RAF. US HEI: they carry 5 gram of total, half-half of 2.5 gram: explosive, 2.5 gram incendiary. I think same as RAF. It would be funny if solid API round carry twice as much as special HE rounds of Hispano...

Figures I have for 20-mm Hispano ammunition:

High Explosive 10.2 grams tetryl
High Explosive Incendiary - 7.0 grams tetryl, 4.3 grams SR379
Semi Armour Piercing Incendiary - 9.2 grams SR379

 

[davebender]

For which ammunition lot?

A bunch of different shell types were produced for the Hs.404 and Hispano Mk II cannon. I believe most of the WWII era Hispano HE ammunition contained about 6 grams of HE.

 

[Shortround6]

Ammunition lots are not going to vary that much. total weight of projectile may vary by a few percent at most. considering the difference in density of HE filler and steel a variation in HE weight of 40-50% would call for a different shell body design.

There were different shells for the Hispano just like there were different shells for the MG 151/20 and just about every other gun that was used for any length of time.

Something to remember when looking at some of the charts in the links provided is that some of the shell weight values seem to be a "nominal" weight or a weight of the various shells in a belt or magazine averaged together.

We could start discussions on which was the best machine gun/cannon of 1940? and of 1942? and of 1944? and answer would change, not because of the gun but because of changes in the ammunition fired.

For instance even such a simple gun as the .303 Browning. The British often didn't mix belts of ammo but loaded different guns with belts of the same ammo. In the BoB a popular mix was 3 guns firing "ball", two guns firing AP, two guns firing MK IV incendiary tracer and one gun firing MK VI Incendiary (De Wilde). In later years Mosquitoes and Spitfires with four .303 guns had two guns firing AP and two guns firing MK VI incendiary/De Wilde ammunition. Half the guns but firing more effective ammunition.

 

[Greyman]

For which ammunition lot?

A bunch of different shell types were produced for the Hs.404 and Hispano Mk II cannon. I believe most of the WWII era Hispano HE ammunition contained about 6 grams of HE.

I don't think I've ever seen figures for a high explosive Hispano round with so little filling. The only one that comes to mind as a possibility is the French High-Explosive/Tracer. I don't have numbers for the HE filling but looking at diagrams I could definately see it in the 4 to 6 gram range.

 

[davebender]

Total projectile weight matters only for AP rounds.

For HE rounds what counts is the amount of explosive filler delivered on target. That holds true for 20mm aircraft cannon shells just as it holds true for army field artillery.

 

[Shortround6]

No, that is not entirely true for aircraft shells and it certainly is not true for army field artillery shells.

And this is dodging the original question. Production tolerances from lot to lot would never be so loose as to allow one batch to have 10 grams of filler and next batch only 5 grams.

Armies spent months if not years and large amounts of money developing shell bodies that would give better/more uniform fragmentation patterns. Fragmentation allows projectiles to damage personnel AND material beyond the blast radius of the HE itself.

 

[Kryten]

Total projectile weight matters only for AP rounds.

For HE rounds what counts is the amount of explosive filler delivered on target. That holds true for 20mm aircraft cannon shells just as it holds true for army field artillery.

actually thats incorrect, a HE round is generally more efficient with a thicker case (within reasonable parameters) due to fragmentation, which is the primary cause of damage, hence the reason grenades have little filler but are specifically designed to produce fragments!
on the Rapier missiles I used to man the warhead was very small but carried fragmentation components to increase the lethal radius!
there is also the issue of case stability upon firing, to achieve a higher velocity, therefore range, the case must be robust enough to accept the firing pressures and acceleration,

 

[tyrodtom]

Artillery shells and aircraft 20mm meant for aircraft use are probably best designed differently. The idea behind the German mine shell ( high filler to shell weight ratio ) was that most of the fragments from a bursting shell was provided by the structure being hit. A conventional 20mm shell just doesn't have enough metal in the shell to provide much fragmentation.
A missile like the Rapier probably in most cases, never actually hits the target, it comes close and explodes, the warhead itself has to provide all the metal for framentation.

The Sidewinder missile had a proximity fuse that would let the range to the target decrease, the millisecond the range began increaseing, the fuse set off the warhead , I would think the Rapier used something similiar.