20MM Hexagon Ammunition

[Jon]

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?

[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

Fritz Hahn in Deutsche Geheimwaffen 1939-1945 Flugzeugbewaffnungen

Of course Tony Williams will be able to expand.

[Juha]

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

[Tomislav Haramincic]

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

[Juha]

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

[wotan]

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)

[Tomislav Haramincic]

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