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Old 12th June 2006, 17:24
Jon Jon is offline
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20MM Hexagon Ammunition

Just come across a reference to 20mm Hex ammunition being especially effective against heavy bombers.
What and how did Hex 20mm differ from standard Luftwaffe rounds?
Why was it so effective?
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Old 12th June 2006, 20:23
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Re: 20MM Hexagon Ammunition

M-Geschoss, both 20mm and 30mm.

HTA-15 (45% Tri-nitrotoluol, 40% Hexogen & 15% Aluminium-Pyroschliff)
HA-41 (75% Hexogen, 20% Aluminium-Pyroschliff & 5% Montanwachs

Fritz Hahn in Deutsche Geheimwaffen 1939-1945 Flugzeugbewaffnungen

Of course Tony Williams will be able to expand.
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Old 13th June 2006, 00:06
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Re: 20MM Hexagon Ammunition

Jon
IIRC from my combat engineer training hexogen has clearly higher burning speed than TNT, so it should be more powerful explosive. IIRC Hex had a burning speed of 8000m/sec and TNT some 6500m/sec, but it was 30 years ago when I needed that info. So probably the rounds had more or less same explosive power but Hex round had 1/3 more ignition material. I don’t know the wax so I cannot say anything on it, maybe it was a stabilizing element. TNT is very safe explosive but Hex was at least sensitive to heat.

HTH
Juha
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Old 13th June 2006, 01:47
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Re: 20MM Hexagon Ammunition

Quote:
Originally Posted by Ruy Horta
M-Geschoss, both 20mm and 30mm.

HTA-15 (45% Tri-nitrotoluol, 40% Hexogen & 15% Aluminium-Pyroschliff)
HA-41 (75% Hexogen, 20% Aluminium-Pyroschliff & 5% Montanwachs
Hello,

Hexogen (RDX) and TNT are the most common explosives used in military explosive compositions. The percentage of these two are set to achieve the desired detonation speed and detonation pressure.
Hexogen or RDX is the more powerfull one, as Juha already said, with density around 1.8 g/cm3.
TNT is less dense, around 1,65 g/cm3. So if you have two same shells and fill one with RDX and the other with TNT, the RDX round will be 35% more powerfull, but also approx. 5 times more sensitive (dificult to handle).
Aluminium dust is used to increase the detonation speed - side effect: it increases also the sensibility.
Wax used in a compositions is just one of many ways to reduce the detonaton speed and sensitivity. For the same purpose for example motor oil or saw dust are used.


regards,
Tomislav
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Old 13th June 2006, 10:10
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Re: 20MM Hexagon Ammunition

Hello Tomislav
and thanks for much more precise explanation on differences between TNT and Hex. My opinion is that if one replaces 45% of TNT by 35% of Hexogen the explosion power doesn’t chance much, The question is the impact of Aluminium dust in the composition. I cannot say anything of its impact on detonation speed (thanks for the correct English term) but I recall that use of it enhance the flash and so my understanding is that the Hex ammo is more destructive if it explode in or near something easily igniting.

Juha
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Old 13th June 2006, 13:43
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Re: 20MM Hexagon Ammunition

Not directly on topic but are you aware of this site?

There are various cut away drawings of different round types (see 20mm Drivers / 30 mm Drivers)
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Old 13th June 2006, 14:21
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Re: 20MM Hexagon Ammunition

Hello,

@ Wotan
excellent site, thanks!


@ Juha
I'm not sure that i have understood you correctly, but I don't think that aluminium powder itself, increases the amount of flash. Aluminium is a good heat conducter with a low melting point, which helps to increse the energy distribution in the composition and simultaniously the detonation speed.
True, aluminium dust is used in flash powder (old fashion photography), but it is used as a fuel - to produce the flash a strong oxidizer must be added (e.g. potassium chlorate or perchlorate).
If you were refering to incendiary rounds, I think that the Luftwaffe also used thermite (simple mixture of aluminum dust and iron oxide) or white phosphorus to produce the incendiary effect.


best regards,
Tomislav

Last edited by Tomislav Haramincic; 14th June 2006 at 03:43.
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Old 13th June 2006, 22:02
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Re: 20MM Hexagon Ammunition

Tomislav
thanks for correction and explanation. And yes, I was thinking Hex round as an HE/I round.

Juha
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Old 14th June 2006, 06:54
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Re: 20MM Hexagon Ammunition

Juha you're welcome.
Perhaps someone else with better chemical knowledge can add here something.

all the best,
Tomislav
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Old 16th June 2006, 21:40
Tony Williams Tony Williams is offline
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Re: 20MM Hexagon Ammunition

Comparing explosives is not simple as there are different aspects to their effectiveness and one which is good in one respect may be less good in another. This is what I put in Flying Guns – World War 2: Development of Aircraft Guns, Ammunition and Installations 1933-45 which I wrote with Emmanuel Gustin:

The types of high explosive chemicals used in shells did vary, although not by as much as might be thought, as different names were used for similar substances. The basic HE in general use was TNT, as used in the Great War. This was often mixed with ammonium nitrate to create Amatol; cheaper but just as effective, except for increased susceptibility to damp. Some use was also made of picric acid, or Lyddite, another First World War explosive.
Before the Second World War, more powerful substances were introduced into service. One of these was PETN, also known as Penta or Penthrite. The problem was that this was generally felt to be too sensitive to use by itself, as it was inclined to be detonated by the shock of firing (although this did not deter the Japanese, as we have seen). It was accordingly usually desensitised by adding about 15% of Montan wax to produce Penthrite Wax, or Nitropenta. An alternative use was to mix PETN with TNT or Amatol to form one of the Pentolites; this actually helped with pouring TNT and Amatol into shells, as by themselves they solidified too quickly and tended to leave holes. Another new explosive, as powerful as PETN but less sensitive, was RDX (Research Department eXplosive), which was also known as Cyclonite or Hexogen.
Aluminium powder was often added to HE, as this both increased the brisance (shattering effect) and enhanced the incendiary effect; an important issue as, for example, some 90% of RAF bomber losses in the war were attributed to fire rather than structural damage. A typical German HEI mix was 63% Penthrite, 29% aluminium and 8% wax, although these proportions did vary. Shell fillings for the 30 mm M-Geschoss typically consisted of 75% Hexogen, 20% aluminium and 5% wax. The (rarely used) M-Geschoss for the BK 3.7 contained a mix of 45% Hexogen, 40% TNT and 15% aluminium. Much use was made of HA.41, a mixture of 80% Cyclonite and 20% aluminium.
Allied explosive fillings included Pentolite, Torpex (a mixture of RDX, TNT and aluminium) and Tetryl or CE (Composition Exploding). The Japanese used several types, with TNT, Pentolite and Cyclonite all being recorded, by themselves or in various combinations. The Soviets used a mixture of RDX and aluminium.
These explosives exhibited some differences in the characteristics, as shown below. The most powerful have not been much exceeded in destructive power since.

I then include a table of characterstics, which I can't copy-and-paste here, but it shows that Hexogen has about 50% more power than TNT (measured as calories per gram x cc per gram) and 100% more brisance or shattering effect, measured by power x velocity of detonation x density. However, it was twice as sensitive.

Tony Williams: Military gun and ammunition website and discussion forum
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