A look at 3 20mm HEI rounds,and their impact in the game(no pun intended)

[brady]

 After visiting the Oregon Military Museum and poring through several Tech Manuals, I managed to come to the following conclusions.(this may or may not be news to you but I was looking to prove that the Hispano from hell has a worthy adversary,It unfortunately has yet to added to the game      )

 The Hispanos contender is the Ho-5 20mm of the Imperial Japanese Army. I did some number crunching aka grade school math (btw it never fails to amaze me how bad at that I can be from time time  so please check my figures       )and came up with the following figures for the HEI rounds for the 20mm M1 & AN-M2 US (hispano) and the Type 99MK II ,and the Ho-5.

Ho-5: length 2 9/16 inches, weight 78.2 grams,filling 11.9 grams,fusing=non.

AN-M29(Hispano): length 3.21inches, weight 130grams, filling 11.31 grams,fusing=yes

Type 99 II: length 3.23 inches, weight 128.86 grams, filling 9.42 grams, fusing=yes


 Ok so what can we determine based on these figures...well the Ho-5 despite being about 3/4 of an inch shorter has the most explosive content, therefore it has the most destructive power on impact of the 3 above, please bear in mind I am only referring to the shells own explosive power not penetration of any armor.
 fusing: why bring it up?, well the fuse represents a big part of the shell as the pics bellow illustrate. What is signistudmuffinent is that the Ho-5 HEI has no fuse the P.E.T.N. is designed to explode by the crushing action of the impact, thus saving space in the shell for more explosive.That is to say that the shell is shorter since it needs no stinking fuses      

Ho-5: ROF 850 rpm, M/V 820 m/s
AN-M2(hispano): ROF 600 to 700 rpm, M/V 840 to 880 m/s
Type 99 II: ROF 490 rpm, M/V 625 m/s

 Now with the Ho-5 higher ROF and the Japanese tendency to load predominantly HEI and the Ho-5 tracer was a AP (see below)round, this would be the ultimate 20mm for killing aircraft.

       

       

 

         


      Brady

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[GRUNHERZ]

20mm mineshell has more explosive than that IIRC it has about 18 grams, cmon lets all say mineshell for the MG151/20!  

[ra]

I agree with what you write, but I find the pictures confusing.

ra

[brady]

  This is the Ho-5 HEI round I referred to above...(the middle pic above is for a Type 99 (mk I & II used the same projectiles)The lower pic is for a Early H0-5 HEI round and since we would likely get a Ki-84 or a Ki-100 as our first Japanese army fighter it is appropriate that we would use the later HEI round pictured bellow.

   

     Brady

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[This message has been edited by brady (edited 12-28-2000).]

[Tony Williams]

The Ho-5 was not as good as you suggest.  Owing to a shortage of quality steel, the cartridge had to be downloaded to avoid breaking the gun.  Muzzle velocity should have been over 800 m/s, but actually was 700-730 m/s.

The Type 99-2 was better than you suggest; muzzle velocity was 750 m/s.

The 92g German M-Geschoss contained 18-20g of HE, the late-war 105g version contained 25g of HE (but I'm not sure how much service use that had).

Don't underrate the kinetic energy advantage of the Hispano/AN-M2.  The heavy projectiles meant that velocity was maintained better, giving a longer effective range (especially useful against bombers or in ground attack).  Furthermore, the API shell could punch through 18mm armour as well as causing great destruction - something that the Ho-5 or the M-Geschoss could not manage.  Early in the war, the nose-fuzes for the HE shell were unreliable so the RAF just used inert steel projectiles - and found them very effective!

Tony Williams
New book: Rapid Fire - The Development of Automatic Cannon, Heavy Machine Guns and their Ammunition for Armies, Navies and Air Forces.
Details on my military gun and ammunition website: http://www.users.globalnet.co.uk/~autogun/
 

[brady]

  Mr. Williams said:

The Ho-5 was not as good as you suggest. Owing to a shortage of quality steel, the cartridge had to be downloaded to avoid breaking the gun. Muzzle velocity should have been over 800 m/s, but actually was 700-730 m/s.
   
 This may very well be the case, that is to say i am not surprised to hear it can U be more specific on this point, how many were affected just certain plants or certain production runs, and at what time did this occur the Ho-5 having bean around a while.It is just that none of my sources mention this..namely TM-1985-5


The Type 99-2 was better than you suggest; muzzle velocity was 750 m/s.

  I thought this M/V was for the late model Type 99 II the mark 5, and if memory serves it did not see much use if any in combat(my sources are a little vague on it, can U clarify)


  On the subject of the AN-M2 against armor I am quiet aware that it was a better AT weapon, that is not a point of conjecture, my main focus is on anti aircraft weapons and it still looks to me that he Ho-5 was a better ,if not marginally so, weapon for this role.

  Correct me if I am wrong, but is not the weight of a shell secondary to it's ballistic shape, for determining its performance at a given range.
  The above point aside can U tell what the comparative dispersion of the H0-5 and the AN-M2 would be at say 1,000ft then 1,500 then 2,000ft.

   Brady

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[brady]

  A shot of the Type 99 I and the 20mm Hispano rounds...

 

         Brady

[Hooligan]

Brady:

I've looked at trajectory information for a number of shells and from what I've seen weight is more important than ballistic shape.   A while back I calculated ballistic coefficients for a variety of Mg151 20mm shells.  All of the BCs for 115g shells fell within the .44 to .48 range.  The BCs for 87g - 90g Mine shells (the rounds have very similar shapes to some of the 115g rounds) were around .27.  Similarly the G1-BC for the identically shaped .50 M2 ball and AP/I rounds are about .72 and .65 respectively.  I believe that the only ballistic difference between these two projectiles is that the ball round is a bit heavier.

With the kinds of guns we are firing in Aces High and at the ranges of interest (roughly out to a 1000 yards), I believe the most important ballistic factors are in Order:

Initial projectile velocity
Projectile sectional density (roughly equating to weight)
Ballistic shape

Since none of the ballistic shapes of any shell are really that bad (like a crumpled up piece of paper for example), it just doesn’t make that much difference out to a few hundred yards.  A round with a bad ballistic shape that starts at 900m/s is still going to get to a target 400m away long before a round with a good ballistic shape starting at 700m/sec is going to.

As far as weight goes:  Suppose you have two 20mm rounds of identical shape and going the same speed.  These rounds both generate the same drag, but….  If one round weighs 100g and the other weighs 130g, then the lighter round will decelerate about 25% quicker.  i.e. the force (drag) operating on their masses is identical but one round weighs 25% less so it will decelerate 25% more.

Hooligan

[niklas]

Does someone of our ammo-experts maybe know which german 20mm round for the mg151 had a electronic fuse?

thx
niklas

[brady]

  Hooligan: Nicely stated ty, so a lighter round that had a higher M/V(Thereby making up for a lack of mass by having a higher initial velocity) would still fair well at our threshold of interest (1,000yards).
  Considering as u stated that most of the types represented in AH have a decent Ballistic shape.

  A curious observation could be made at this point, in most cases it could be said that since the tracer rounds are lighter they drop faster than the Ball (or solid) shot they are flying along with. In the case of the Ho-5 it's tracer ammo is heavier than the rest of the ammo in the chain so it would do the opposite,correct? But if this were known would not the powers to be compensate by lessoning the powder load for them so they would be more representive of the flight path for the rest of the ammo?

       
               Brady
 

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[This message has been edited by brady (edited 12-29-2000).]

[Hooligan]

Ideally, whoever was making the guns and ammunition would tailor the propellant charge and projectile weight so that the various types of rounds would have roughly similar trajectories out to 1,000 yards or so.  I know that to some extent they did so:  For example, I know of at least one AP round that has a lightweight inert core so that its weight is not drastically different than other rounds for the same gun.

For rounds with roughly the same mass, I would think it would be pretty feasible to match ballistics well enough.  But I also think that extreme conditions, like firing when pulling heavy G's make the trajectories diverge quite a bit more than they would under normal conditions.

I expect the Japanese probably did tailor the Ho-5 rounds to match ballistics.  Frankly it would have been a bit stupid not to do so, and as far as I can tell, everybody did a pretty good job at designing aircraft weapons that were effective at killing their intended targets.  

Hooligan

[Hooligan]

Niklas:

email Gerzzz (gerzzz@bf109.de.) and ask him.  He will tell more than you want to know about German fusing.

Hooligan

[Tony Williams]

Originally posted by brady:
 Mr. Williams said:

The Ho-5 was not as good as you suggest. Owing to a shortage of quality steel, the cartridge had to be downloaded to avoid breaking the gun. Muzzle velocity should have been over 800 m/s, but actually was 700-730 m/s.
   
 This may very well be the case, that is to say i am not surprised to hear it can U be more specific on this point, how many were affected just certain plants or certain production runs, and at what time did this occur the Ho-5 having bean around a while.It is just that none of my sources mention this..namely TM-1985-5

AGW - My source is a restricted US Military Intelligence Division report on Japanese 20mm ammunition, dated July 1945.  They tested the muzzle velocities of the Ho-5 rounds and found that the HEI did 2,400 fps, the AP-T 2,300 fps, equivalent to 730 and 700 m/s.  As far as gun weakness is concerned, this information comes from Ted Bradstreet, an American enthusiast of Japanese aircraft guns who probably knows more about them than anyone - period.

The Type 99-2 was better than you suggest; muzzle velocity was 750 m/s.

  I thought this M/V was for the late model Type 99 II the mark 5, and if memory serves it did not see much use if any in combat(my sources are a little vague on it, can U clarify)

AGW - I think you are confusing muzzle velocity with rate of fire.  The Type 99-2 had a 101mm case length, compared to 72mm for the Type 99-1.  So, the mv went up from 600 to 750 m/s.  I have both in my collection and they are very different!

  Correct me if I am wrong, but is not the weight of a shell secondary to it's ballistic shape, for determining its performance at a given range.

AGW - both are important, but all cannon shells of that era had a poor shape in comparison with bullets (see my post about ballistic coefficients at http://www.delphi.com/autogun/messages/

  The above point aside can U tell what the comparative dispersion of the H0-5 and the AN-M2 would be at say 1,000ft then 1,500 then 2,000ft.

AGW - sorry, I have no info on that.  It would depend on the mountings (how stiff they were) and any such variations would probably be minor in comparison with the errors caused by aircraft movement and vibration anyway.

Tony Williams
New book: Rapid Fire - The Development of Automatic Cannon, Heavy Machine Guns and their Ammunition for Armies, Navies and Air Forces.
Details on my military gun and ammunition website: http://www.users.globalnet.co.uk/~autogun/

[Tony Williams]

 

Originally posted by niklas:
Does someone of our ammo-experts maybe know which german 20mm round for the mg151 had a electronic fuse?

thx
niklas

AFAIK none did.  They used either mechanical or percussion (detonator) type fuzes.  You might be confusing this with electric ignition of the cartridge.  The MG 151 was built with both percussion and electric primers.  Ammo was not interchangeable.

Tony Williams
New book: Rapid Fire - The Development of Automatic Cannon, Heavy Machine Guns and their Ammunition for Armies, Navies and Air Forces.
Details on my military gun and ammunition website: http://www.users.globalnet.co.uk/~autogun/

[brady]

  Mr. Williams said:

AGW - My source is a restricted US Military Intelligence Division report on Japanese 20mm ammunition, dated July 1945. They tested the muzzle velocities of the Ho-5 rounds and found that the HEI did 2,400 fps, the AP-T 2,300 fps, equivalent to 730 and 700 m/s. As far as gun weakness is concerned, this information comes from Ted Bradstreet, an American enthusiast of Japanese aircraft guns who probably knows more about them than anyone - period.

 Could u give me the Number of the report so that I may look it up I would love to read it, I have had the pleasure of speaking with Ted Bradstreet,and have had correspondence with him, In fact he is the one who helped to spark my interest in this weapon, regrettably he did not mention this aspect of the guns performance to me, I will have to get in touch with him on this matter.

 AGW - I think you are confusing muzzle velocity with rate of fire. The Type 99-2 had a 101mm case length, compared to 72mm for the Type 99-1. So, the mv went up from 600 to 750 m/s. I have both in my collection and they are very different!

 I am well aware of the differences in the shells for the type 99 , I have put my hand on them myself. I even refer to that in an above post. The projectiles were the same however.
 I was referring to the different marks of the Type 99 II: MK3,MK4,MK5.rate of fire ranging from 490rpm to 750 rpm, M/V ranging from 1,970ft per sec to 2,490ft per sec(model II MK5)

The above point aside can U tell what the comparative dispersion of the H0-5 and the AN-M2 would be at say 1,000ft then 1,500 then 2,000ft.

 Well what I was getting at is do the have a significant difference in drop at range(I could of been clearer on this point sorry)


                       Brady

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[This message has been edited by brady (edited 12-30-2000).]