Shaped charge warheads and overpenetration

[z0boson]

Hello,

I was wondering how to treat an attack by a shaped charge warhead (like HEAT and HEMP rounds) after it hit a first barrier. If a target is standing a few meters/yards behind a wall and is hit by an over penetrating attack, should the attack still have the full armor devisor or should it be reduced, as the charge is not correctly focused anymore?

Thanks in advance for your help!

[The Colonel]

Originally Posted by z0boson

Hello,

I was wondering how to treat an attack by a shaped charge warhead (like HEAT and HEMP rounds) after it hit a first barrier. If a target is standing a few meters/yards behind a wall and is hit by an over penetrating attack, should the attack still have the full armor devisor or should it be reduced, as the charge is not correctly focused anymore?

Thanks in advance for your help!

For a single stage warhead, I'd recommend stripping off all the armour divisor and treating it as nothing more than an explosion - especially meters away (consider that schuzeren or bar armour a matter of inches away can seriously interfere with penetration). Multi-stage warheads would just lose a stage.

Someone around here probably has some physics that will give you more detail...

[Nereidalbel]

Armor divisors on explosives only apply to targets that take a direct hit. Thus, the guy standing nearby is only hit by a normal explosion.

[z0boson]

Originally Posted by The Colonel

For a single stage warhead, I'd recommend stripping off all the armour divisor and treating it as nothing more than an explosion - especially meters away (consider that schuzeren or bar armour a matter of inches away can seriously interfere with penetration). Multi-stage warheads would just lose a stage.

Someone around here probably has some physics that will give you more detail...

Thank you for your answer. Now I realize that I don't really understand what happens with the shaped charge after penetration. Does the explosion "fill" the space behind it or is it still directional (like a cone)? For example, if a vehicles is hit by a HEAT warhead, is all the crew hit by the explosion?

One of my players had the idea to use a riot shield as defense against HEMP micro missiles. This would actually be a good strategy then...

[z0boson]

Originally Posted by Nereidalbel

Armor divisors on explosives only apply to targets that take a direct hit. Thus, the guy standing nearby is only hit by a normal explosion.

While I understand this rule for targets standing around the detonating warhead, and only getting hit by the non-directional effect, I am not sure if it can equally be applied to targets directly in front of the directional attack. Maybe it does, I just would like to know if the rule reflects the reality of this sort of attacks, as they are quite common in my campaign (TL 10).

If I understand it right, the shaped charge creates a jet of molten metal. Naively, I would imagine that this behaves like a projectile for some distance before dissipating.

[lwcamp]

Originally Posted by z0boson

Thank you for your answer. Now I realize that I don't really understand what happens with the shaped charge after penetration. Does the explosion "fill" the space behind it or is it still directional (like a cone)? For example, if a vehicles is hit by a HEAT warhead, is all the crew hit by the explosion?

A shaped charge jet is a narrow stream of hypervelocity metal (from the liner) and some assorted crud from the exploded explosives. It typically propagates 2 to 3 meters before breaking up, past which it loses most of its penetrating power. Smaller shaped charges don't go as far, larger charges go farther. So - no over-penetration to anything more than a couple of meters behind the first barrier. Within that first couple of meters, I would apply normal GURPS rules - roll damage and treat the first thing as cover DR.

You can treat this jet as a separte thing from the explovie blast. The jet reaches the target first and blows out a narrow hole; the blast arrives later and is going in all directions.

Luke

[z0boson]

Originally Posted by lwcamp

A shaped charge jet is a narrow stream of hypervelocity metal (from the liner) and some assorted crud from the exploded explosives. It typically propagates 2 to 3 meters before breaking up, past which it loses most of its penetrating power. Smaller shaped charges don't go as far, larger charges go farther. So - no over-penetration to anything more than a couple of meters behind the first barrier. Within that first couple of meters, I would apply normal GURPS rules - roll damage and treat the first thing as cover DR.

You can treat this jet as a separte thing from the explovie blast. The jet reaches the target first and blows out a narrow hole; the blast arrives later and is going in all directions.

Luke

Thanks Luke, that was very helpful. In my campaign I am mostly concerned about very small blasts from gyroc warheads. So using a riot shield at arms length might not offer much protection, but standing a few meters behind a wall will. I am toying with the idea to reduce the armor penetration one step (10/5/3/2/1) for every meter to simulate the dissipation of the beam.

[Fred Brackin]

Originally Posted by lwcamp

A shaped charge jet is a narrow stream of hypervelocity metal (from the liner) and some assorted crud from the exploded explosives. It typically propagates 2 to 3 meters before breaking up, past which it loses most of its penetrating power. Smaller shaped charges don't go as far, larger charges go farther. So - no over-penetration to anything more than a couple of meters behind the first barrier.

When the Mythbusters attempted to re-create the "magnum pistol v. RPG" stunt from the movie Red they were getting high velocity droplets of molten metal something like 80 ft downrange. this would not be an efficient attack. Perhaps no more than 1 or 2 D of Burn damage.

On the other end, even the full concussion from the detonation of an RPG-7 had no significant effect just 10 feet away. Particularly for small weapons I would ignore the possibility of concussion damage coming in through the hole made by the jet. Even if it woks that way and you go through the calculations you won't get meaningful damage. Concussion falls off _very_ fast.

[z0boson]

Originally Posted by Fred Brackin

On the other end, even the full concussion from the detonation of an RPG-7 had no significant effect just 10 feet away. Particularly for small weapons I would ignore the possibility of concussion damage coming in through the hole made by the jet. Even if it woks that way and you go through the calculations you won't get meaningful damage. Concussion falls off _very_ fast.

That is of course true. Still, if the target is right behind the wall or a shield, it might have some effect.

[Nereidalbel]

Originally Posted by z0boson

That is of course true. Still, if the target is right behind the wall or a shield, it might have some effect.

If they're in-line with the charge, a stream of molten copper tends to be very bad for your health. Otherwise, they might be knocked down and experience a bit of bruising. Granted, that should be a Fright Check for anybody who isn't Unfazable.