[UT, HT, Basic] Explosive rounds & damage "blow-through"

[LokRobster]

How do you determine where an exploding bullet explodes?

Milam was interested in the way Ryne had killed the shaugarr. When Ryne pointed out the hole made by the slug's entry, the old man was incredulous. He protested, "This is only a small hole, Ryne. Our javelins do better. How can it kill? Where did all the blood come from?"

"Let's look at the other one. You'll see it better."

They stood in the blood-soaked dirt beside the first shaugarr and studied the fallen beast. It was a full four meters long from muzzle to the tip of the stubby tail. The broad red stripe running from shoulder to haunch was broken by an eruption of bloody flesh, shattered bone, and intestine where Ryne's bullet had emerged, tearing the right rear leg half off.

"It makes a bigger hole coming out," Ryne said.
excerpt from Law for the Stars by John Moressey

Background:
I am working up my favorite sci-fi background by author John Moressey - often called the "Del Whitby" trilogy, a series of 6 loosely tied together books set in a retro-tech galaxy ~400 to 700 years in the future. Not a "guns" expert, he has used some interesting weapons in his stories that I am converting to GURPS stats.

As an example, I'm looking at Sternverein Security trooper's weapon, a TL9 slugthrower that shoots a "thumb-sized" bullet that is described as leaving a much larger hole exiting than it does entering. Some of the author's gun and wound details seem like explosive shells more than hollow-point; one scene has a guy blow 3 meter wide hole in 2 meter tall old dead fallen tree log! I figure that the wood is completely dry and rotted, and a hole that large could only be the result of an explosion.

Throughout the series the weapon of the Sternverein is considered to be a one-shot kill on an average unarmored humanoid. The standard TL9 shotgun pistol loaded w/ HE ammo seems to be very close to what I envision...

The Crux:
My gun is a 12 gauge (18.5mm) HE shell, doing 4d pi++ (0.5) with a linked 2d cr ex [1d]. How often will the explosion occur inside a target? Does the cutting fragmentation damage happen inside them too?

Is there a torso "blowthrough" damage maximum? Probably i am remembering 3rd Ed, but i can't find anything in 4th Ed. Does the linked effect always occur if nothing is blowing through?

I know there are HT/2 limits on limbs & HT/3 on hands/feet; does that mean the explosive damage will occur elsewhere? Or on a leg hit can the 4d++ take effect (likely maxing out HT/2) and then the 2d cr ex separately damage up to HT/2 as well?

And how does linked explosive damage affect Overpenetration [Basic pg408]? 4d++ will go through an unarmored 10 hp person very often, (even treating the DR0 as DR1 due to the fractional armor divisor) but if the shell itself has exploded then maybe only the explosive damage & fragmentation would make it to anything behind the main target?

If a DR6 steel breastplate wearer's armor soaks up all the 4d pi++ (0.5) damage, does the linked damage explode on the target's chest?

Thanks in advance for your thoughts and patience with my rambly writing style.

[LokRobster]

Milam was silent for a time, then he knelt and laid his hand on the shaugarr's shoulder and spoke under his breath. Rising, he said to Ryne, "It is a bad way to die."

"They're all bad, Milam."

"This way is without dignity. There is no chance. It tears apart, destroys; it does not merely take the life. I fear these weapons of yours, Ryne. They are too powerful. Think what would happen if they were used upon a man!"

Ryne knew what happened, but he said nothing...

[apoc527]

That's not an explosive shell. An explosive bullet would explode internally, and not leave an exit wound. The wound description you provided is the standard wound for a high velocity projectile. My guess is the "thumb sized" bullet is going rather fast...perhaps rifle velocities. That would cause a huge exit wound.

[LokRobster]

Interesting, good to know. Something like the 14.5mm anti-tank rifle?

Huge piercing (p++) doesn't gain anything by being hollow-point; I don't know of a way to get a higher damage multiplier so perhaps it's just monstrous base damage.

The author gives the Sternverein gun a 9" barrel. I'm sure the weapon effects are based more on plot and poetic impact rather than actual physics!

[Nereidalbel]

Just sounds like a TL9 version of a Barrett .50 cal to me. Super-dense material travelling at super-sonic speeds = one dead beast. Either that, or the bullet expands far faster than the rounds we use today.

[lexington]

Originally Posted by LokRobster

Huge piercing (p++) doesn't gain anything by being hollow-point; I don't know of a way to get a higher damage multiplier so perhaps it's just monstrous base damage.

Other than easy of play (and possibly balance) there's no reason not to have the progression continue.

lwcamp has house rules that follow the SizeSpeedRange table. http://panoptesv.com/RPGs/HouseRules/ImpPierce.html

A bullet that does 4d damage with a x3 multiplier would be close to an automatic kill on an an unarmored human (if you don't apply blowthrough rules) followed by insanely severe bleeding if they live through it.

Originally Posted by LokRobster

The author gives the Sternverein gun a 9" barrel.

That suggests a weapon about the size of an MP5 submachine gun. Larger than a pistol but smaller than a rifle.

[Ulzgoroth]

Originally Posted by apoc527

That's not an explosive shell. An explosive bullet would explode internally, and not leave an exit wound. The wound description you provided is the standard wound for a high velocity projectile. My guess is the "thumb sized" bullet is going rather fast...perhaps rifle velocities. That would cause a huge exit wound.

An explosive bullet doesn't stop having forward momentum just because it exploded. Exploding would make it expand more and penetrate less, but not necessarily stop it without an exit wound.

The little hole in front big hole in back thing doesn't require exploding rounds. Expanding or fragmenting ones can certainly do it. I wouldn't think non-deforming bullets would, but I could be wrong. But it doesn't rule out exploding bullets either.

[lexington]

Originally Posted by Ulzgoroth

An explosive bullet doesn't stop having forward momentum just because it exploded. Exploding would make it expand more and penetrate less, but not necessarily stop it without an exit wound.

The little hole in front big hole in back thing doesn't require exploding rounds. Expanding or fragmenting ones can certainly do it. I wouldn't think non-deforming bullets would, but I could be wrong. But it doesn't rule out exploding bullets either.

Wouldn't an explosion inside of a person produce nasty effects at the front, as well? I can't find any videos of explosions inside ballistic gel or anything like that but the path of least resistance is presumably to follow the entry wound back out. I suspect this gun is meant to be an exaggeration of how the 5.56 NATO was advertised as blowing out a baseball sized chunks of flesh.



The discussion of how to treat an internal explosion is still worth having to HT and UT weapons. For a UT gun it should go off perfectly every time and for a HT gun I expect there would be a significant change of the bullet passing through before it detonates. As far as I know there are no explosive bullets designed to be used on human targets so information is lacking.

We could say it has a skill of 12 and TL 8, a skill of 14 at TL 9, and a skill of 16 at TL10, and gets a bonus equal to SM. If it fails the roll it goes off behind he target as a normal explosion. If its stopped by armor it is a contact explosion.

That doesn't seem wildly unreasonable to me at first glance.

[Nereidalbel]

Originally Posted by lexington

Wouldn't an explosion inside of a person produce nasty effects at the front, as well? I can't find any videos of explosions inside ballistic gel or anything like that but the path of least resistance is presumably to follow the entry wound back out. I suspect this gun is meant to be an exaggeration of how the 5.56 NATO was advertised as blowing out a baseball sized chunks of flesh.



The discussion of how to treat an internal explosion is still worth having to HT and UT weapons. For a UT gun it should go off perfectly every time and for a HT gun I expect there would be a significant change of the bullet passing through before it detonates. As far as I know there are no explosive bullets designed to be used on human targets so information is lacking.

We could say it has a skill of 12 and TL 8, a skill of 14 at TL 9, and a skill of 16 at TL10, and gets a bonus equal to SM. If it fails the roll it goes off behind he target as a normal explosion. If its stopped by armor it is a contact explosion.

That doesn't seem wildly unreasonable to me at first glance.

Explosive rounds vs ballistic gel for ya

[lexington]

Originally Posted by Nereidalbel

Explosive rounds vs ballistic gel for ya

Those rounds are explosive in the sense that they are frangible and thus "explode inside the target" not that they're loaded with an explosive. It's slightly outdated wording that is a great modern marketing buzzword.