HEP vs HE

[Nemesis Lead]

Guys,

In terms of the 105mm rounds fired by the gun variant of the Stryker....I am assuming that the difference between High Explosive rounds and High Explosive Plastic rounds is that the explosive in the latter is plastic explosive.

A few questions:

1) Is this correct?

2) Are there advantages or disadvantages in using HE-P vs HE?

3) Assuming that HE-P is more powerful than standard HE...why aren't all HE rounds HE-P rounds?

Many thanks,

Jay

[Guest Mike]

HEP has an anti-armour (& anti-bunker) function, and IIRC it can be sub-optimal for engaging your basic foot walking infantry in the open as the round explodes when teh base fuse strikes something - if the "something is earth then the HE part of the round can be partially smothered by having penetrated.

[Nemesis Lead]

Thanks, SO.

That sounds like High Explosive Squash Head (HESH). Are HESH and HE-P the same thing?

[John Kettler]

Nemesis Lead,

HESH and HEP are the same thing under different acronyms. The former's British, the latter American.

Regards,

John Kettler

[Michael Emrys]

Also, I wonder if HEP is in a casing that fragments as well as a standard HE.

Michael

[John Kettler]

Michael Emrys,

Would rather doubt it, seeing as how HEP is designed to mold itself to the target on impact. This would seem to rule out the substantial hardened steel shell walls commonly found on HE projectiles. Suggest you check www.battlefield.ru under artillery projectiles for comparative section drawings.

Regards,

John Kettler

[Nemesis Lead]

Thanks John. Do you know if the plastic explosive used in HE-P is more powerful per unit of weight than regular HE?

[Michael Emrys]

Originally posted by John Kettler:

...seeing as how HEP is designed to mold itself to the target on impact. This would seem to rule out the substantial hardened steel shell walls commonly found on HE projectiles.

That was precisely my thought.

Michael

[John Kettler]

Nemesis Lead,

Off the top of my head, no, but the numbers comparing, say, C4 (for HEP) with TNT (for HE) are certainly available on the net, most likely in a table which uses TNT as the baseline for comparison.

Regards,

John Kettler

[Sykes]

High Explosive Plastic (HEP)

Shell Shell with deformable nose, designed to contain a plastic explosive, for use against armor; shock transmitted through the armor causes the back of armor plate to spall. Also referred to as Squash-Head Shell.

(from Hydrocut.com)

I really don't know why they use this instead of HEAT, maybe its cheaper to produce than the shaped charge. I wouldn't use this though against MBT armor, most of the plastique's power transmitted will blast to outside because the lack of damping. Just like Stalin's Organist mentioned, the bunkerbusting ability might be the key issue. Light infantry doesn't have too many armor threats anyways and i presume they have HEAT rounds for those 105mm's as well.

[Kurtz]

HEAT will make a small hole in a concrete wall, HEP/HESH will blow away the concrete over a larger area.

However, the steel reinforcement (if any) may still be intact and prevent entry.

IIRC, HEP/HESH is less effective against armour with layers of different materials or with air spaces between layers of armour.

[flamingknives]

AIUI, HESH has a larger proportion of HE for a given shell size due to the thinner shell walls. The explosive is no more powerful, there's just more of it. Nonetheless, the walls still have to be substantial to withstand in excess of 5000g's of acceleration on firing.

Some HESH rounds have smart fuzing that can differentiate between the surface struck and detonate accordingly. They are extraordinarily effective at breaching concrete and the like - originally HESH was developed for anti-fortification work. Against light vehicles, HESH is devastating and will probably do severe external damage (sights and the like) even when it has no chance of penetrating the armour.

Compared to HEAT, even multipurpose HEAT, HESH yields better HE effect for a given calibre.

Finally, HESH is vastly cheaper than HEAT rounds, as the latter requires micron tolerances on the liner, sophisticated fusing (point detecting, base detonating) and a high quality of explosive just to work. To make it into a multipurpose round requires the use of fancy fragmentation jackets made of, amongst others, tungsten, which is a sod to work with and horribly expensive.

[John Kettler]

Sykes,

Welcome! (if I haven't done so already)

flamingknives is spot on with his incisive commentary, but probably low by a factor of twenty

on the projectile G load at launch. ISTR the U.S. Copperhead, launched from the relatively low velocity 155, had to withstand 100,000 Gs, but my memory may be shorting out, too.

flamingknives,

Where HESH really shines is against old school monobloc armor. Saw interior shots of a T-55 hit in the turret rear in the 1967 War. The HESH hit knocked a spall chunk loose as big as a pie tin and sent it whistling through the tank. Could tell this was so because the spall chunk first went right through the radio, leaving a more or less neat hole from back to front of the transceiver. Suspect that Chobham and similar would be very effective protection vs. HESH.

Regards,

John Kettler

[flamingknives]

5,000 G, 100,000 G, it's all a factor of wah? higher than most people's comprehension.

5,000 G is the minimum acceleration needed to attain 800m/s from a 55 calibre, 120mm bore barrel. Peak acceleration in real life is obviously higher, but probably not half as high 100,000 G, even from a tank gun.

John's right that HESH is very effective against monoblock armour, plus it also has the added bonus that it is relatively insensitive to angle - plate thickness is the only important factor until you are way past 60 degrees from the vertical.

Interestingly, the Challenger 2 KO'd in Operation Telic (what the Brits did during OIF) was destroyed by a HESH shell.

The armour wasn't comprimised - it hit the open commander's hatch and detonated, killing the turret crew and setting off secondary deflagrations/explosions from stored HESH shells*.

*Not the charges though, Challenger 2 uses two-part ammunition and the propellant charges are stored outside the fighting compartment.