Steve Jackson Games - Site Navigation
Home General Info Follow Us Search Illuminator Store Forums What's New Other Games Ogre GURPS Munchkin Our Games: Home

Go Back   Steve Jackson Games Forums > Roleplaying > GURPS

Reply
 
Thread Tools Display Modes
Old 03-31-2016, 04:20 PM   #1
FF_Ninja
 
Join Date: Feb 2016
Default Bullets: Overpenetration, Tumbling, Traveling

So, in prep for the modern campaign I'm running, I've been pouring over [what I expect to be] one of the more important systems I'll need to be familiar with: gun combat. One particular aspect - round behavior upon impact - has been touched on in various threads and boards, but I feel like there's a disconnect.

So far, just about every thought I've read about rounds has to do with varying damage - I.E. larger caliber rounds doing more "damage" than smaller caliber rounds (which, frankly, I believe is patently false). I've yet to find anyone touch upon the nuances of what a round does after it impacts - other than the general idea which is, "getting shot sucks" (which is patently true).

To further define the issue at hand: small caliber rounds have a tendency to tumble when they impact (resulting in more internal damage) and travel when impacting a bone, as opposed to their larger caliber brethren which generally just over-penetrate. Range is a factor, too: shoot a dude at point-blank with a .308 and it'll tend to make a clean (albeit large) hole front-to-back; the same shot at a more optimal distance would have decelerated a bit already.

I'm envisioning a situation where, say, a Russian agent with a .22LR pistol pops someone dissident the skull (old KGB style), and the round penetrates only the first layer of bone but then proceeds to tumble and travel, turning said dissident's brains into scrambled eggs. A through-and-through shot from a heavier caliber weapon wouldn't do that.

Are there any supplements that deal with these issues? Have any of you run a session where you (or one of your players) felt it important to address the nuances of different caliber ammunition, and at different ranges?
FF_Ninja is offline   Reply With Quote
Old 03-31-2016, 06:29 PM   #2
Boomerang
 
Boomerang's Avatar
 
Join Date: Feb 2016
Location: Melbourne, Australia (also known as zone Brisbane)
Default Re: Bullets: Overpenetration, Tumbling, Traveling

What is the advantage in going to that level of detail?

Damage has a random element, it is already possible for a small calibre round to do more damage than a larger calibre. When that happens you have a in game explanation (the larger round passed through without hitting anything important).

This big disadvantage in making combat more detailed is that it slows down considerably.

But if you are determined to add more realism, there was a really great Mythbusters episode where they looked at the penetrating power of different calibre weapons when fired into a pool of water, that you might want to check out.
Boomerang is offline   Reply With Quote
Old 03-31-2016, 07:21 PM   #3
FF_Ninja
 
Join Date: Feb 2016
Default Re: Bullets: Overpenetration, Tumbling, Traveling

Quote:
Originally Posted by Boomerang View Post
But if you are determined to add more realism, there was a really great Mythbusters episode where they looked at the penetrating power of different calibre weapons when fired into a pool of water, that you might want to check out.
Well, I've got a decent grasp of the kind of damage rounds do when they penetrate. I've observed slow-mos of ballistic gel, read some articles, and even seen a few relevant examples in real life.

I just wasn't sure the discrepancy between ammunition calibers was considered in the game supplements. If it was, I'd sure like to know which one so I can read up on it. :) I find half the interest in loading out a character with a gun is also choosing ammunition and having an idea of what it does.
FF_Ninja is offline   Reply With Quote
Old 03-31-2016, 07:38 PM   #4
Anaraxes
 
Join Date: Sep 2007
Default Re: Bullets: Overpenetration, Tumbling, Traveling

Calibre maps to the 'p' pluses and minuses. Powder load is energy, which maps to damage. Anything beyond that is really below resolution. It's not like some rounds always tumble and others never do, or that on a hit point scale from 1-50 it's going to make a lot of difference.

For that matter, the experts still argue about the exact means of bullet damage and which sorts are better. (Sure, there's plenty of people with confident assertions on the Internet -- but nobody really knows, and it's not that certain of a topic.)

High-tech has rules for different sorts of ammo. Tactical Shooting goes into a lot of detail. There's also Gun-Fu for the action-movie style of gunplay. There's also a couple of supplements with more gun stats (Pulp Guns, Adventure Guns).

Douglas Cole has a spreadsheet that's good for calculating damage for all sorts of cartridges and weapons that aren't already in a book.
Anaraxes is online now   Reply With Quote
Old 03-31-2016, 08:10 PM   #5
FF_Ninja
 
Join Date: Feb 2016
Default Re: Bullets: Overpenetration, Tumbling, Traveling

Thanks! You've been a big help!
FF_Ninja is offline   Reply With Quote
Old 03-31-2016, 08:42 PM   #6
Ulzgoroth
 
Join Date: Jul 2008
Default Re: Bullets: Overpenetration, Tumbling, Traveling

Quote:
Originally Posted by FF_Ninja View Post
So far, just about every thought I've read about rounds has to do with varying damage - I.E. larger caliber rounds doing more "damage" than smaller caliber rounds (which, frankly, I believe is patently false).
Well good news: it is! Larger calibers may have more or less damage. There's a correlation, within a particular class of rounds (rifle or pistol) between bigger and more powerful, but it's not remotely absolute.

Larger calibers do directly correspond to higher wounding factors, in a chunky sort of way (and with an exception for small-caliber high-speed rifle rounds). This is Basic material, but particularly addressed on High Tech 163.
Quote:
Originally Posted by FF_Ninja View Post
I've yet to find anyone touch upon the nuances of what a round does after it impacts - other than the general idea which is, "getting shot sucks" (which is patently true).
Ultimately, what happens is injury, and maybe if you use the right optional rules some bleeding and (very optionally) a long-term side effect. Martial Arts has the most advanced version of the wounding rules, I believe.

What exactly happens with the bullet in the process of this is of academic interest, not game-mechanical significance. GURPS does not have a hugely detailed system for trauma.
Quote:
Originally Posted by FF_Ninja View Post
To further define the issue at hand: small caliber rounds have a tendency to tumble when they impact (resulting in more internal damage) and travel when impacting a bone, as opposed to their larger caliber brethren which generally just over-penetrate. Range is a factor, too: shoot a dude at point-blank with a .308 and it'll tend to make a clean (albeit large) hole front-to-back; the same shot at a more optimal distance would have decelerated a bit already.
Tumbling has a lot to do with the balance of particular rounds. I'm not sure size is really much of a determinant. And I'm quite curious as to whether .308 is really more likely to tumble at lower speeds?

Incidentally, both 5.56mm and .308 fall within the same division of sizing for GURPS purposes: they only are credited with pi (rather than pi-) due to high speed, which probably has to do with bullets yawing or tumbling after impact. (It does explicitly in the case of the 5.56, per Tactical Shooting p61.)

Particularly relevant rules for terminal ballistics include High Tech p162: Body Hits and the aforementioned Tactical Shooting p61. Martial Arts advanced wounding rules aren't gunshot-specific but are likely to be something you want if this is where your thinking is.

Overpenetration is in the Basic Set. It is probably overgenerous with respect to the behavior of some less stable solid bullets after penetrating one target. A bullet from an M-16 that's tumbled and torn itself to pieces isn't going to fly well past the first person it hits.
Quote:
Originally Posted by FF_Ninja View Post
I'm envisioning a situation where, say, a Russian agent with a .22LR pistol pops someone dissident the skull (old KGB style), and the round penetrates only the first layer of bone but then proceeds to tumble and travel, turning said dissident's brains into scrambled eggs. A through-and-through shot from a heavier caliber weapon wouldn't do that.
...You're really going with 'a large-caliber shot through your entire brain wouldn't be so bad' as your test claim here?

I mean, it's possible (though probably extraordinarily unreliable) for a lighter round bouncing off bone to result in more internal damage, but you pick shot through the brain for your example?

I suspect the GURPS answer to 'bullets sometimes ricochet around inside somebody's body like a deranged wasp' is 'that's a critical hit result, that is'. Bullets tumbling, fragmenting, and the like is factored directly into their wounding factor.
__________________
I don't know any 3e, so there is no chance that I am talking about 3e rules by accident.
Ulzgoroth is offline   Reply With Quote
Old 03-31-2016, 08:46 PM   #7
DouglasCole
Doctor of GURPS Ballistics
 
DouglasCole's Avatar
 
Join Date: Sep 2004
Location: Burnsville, MN
Default Re: Bullets: Overpenetration, Tumbling, Traveling

Quote:
Originally Posted by FF_Ninja View Post
Are there any supplements that deal with these issues? Have any of you run a session where you (or one of your players) felt it important to address the nuances of different caliber ammunition, and at different ranges?
Here's an old article that still might be of use to you.

PM me with your address for the latest spreadsheet.
__________________
Gaming Ballistic, LLC
DouglasCole is online now   Reply With Quote
Old 04-01-2016, 12:35 AM   #8
Tomsdad
 
Join Date: Jan 2010
Location: Brighton
Default Re: Bullets: Overpenetration, Tumbling, Traveling

Quote:
Originally Posted by FF_Ninja View Post
So, in prep for the modern campaign I'm running, I've been pouring over [what I expect to be] one of the more important systems I'll need to be familiar with: gun combat. One particular aspect - round behavior upon impact - has been touched on in various threads and boards, but I feel like there's a disconnect.

So far, just about every thought I've read about rounds has to do with varying damage - I.E. larger caliber rounds doing more "damage" than smaller caliber rounds (which, frankly, I believe is patently false). I've yet to find anyone touch upon the nuances of what a round does after it impacts - other than the general idea which is, "getting shot sucks" (which is patently true).

To further define the issue at hand: small caliber rounds have a tendency to tumble when they impact (resulting in more internal damage) and travel when impacting a bone, as opposed to their larger caliber brethren which generally just over-penetrate. Range is a factor, too: shoot a dude at point-blank with a .308 and it'll tend to make a clean (albeit large) hole front-to-back; the same shot at a more optimal distance would have decelerated a bit already.

I'm envisioning a situation where, say, a Russian agent with a .22LR pistol pops someone dissident the skull (old KGB style), and the round penetrates only the first layer of bone but then proceeds to tumble and travel, turning said dissident's brains into scrambled eggs. A through-and-through shot from a heavier caliber weapon wouldn't do that.

Are there any supplements that deal with these issues? Have any of you run a session where you (or one of your players) felt it important to address the nuances of different caliber ammunition, and at different ranges?
Others have already cited the more detailed supplements for this, but suffice to say effect on target in GURPS is a combination of penetration power (damage) injury multiplier (pi-, pi, pi+ & pi++) and specific rules like over-penetration, injury location, bleeding etc.

All these combine to give a wide variety of end effects in different situations with different bullets. Remembering also the effect on living targets has many variables due to the target as well as variables from what you've shot them with.

Stuff like tumbling is specifically cited as being part of this. As already mentioned the 5.56x45mm round (and other lighter rifle rounds) has been looked at. It has been given a boost in terms of injury type. They would by calibre be pi-, but are in fact pi. This is due in part to tumbling in the wound, which itself is partly* an effect of high velocity. However it makes the point that if velocity is not high (so shorter barrelled rifles/carbines) past certain distances that boost should be withdrawn dropping the injury type to pi-


Lets take you execution of the dissident as an example of all this.

A .22LR out of pistol is going to be 1d+1 pi- and we'll assume the dissident is HP10 and HT10.

right so the round will do between 2 and 7 points of penetrative damage but the skull is DR2 which means you will be left with 0-5 point do damage beating the skull.

This is not unreasonable .22's have been stopped by skulls before. In fact that travelling you describe can be that, where the bullet enters the scalp but having been stopped by the skull travels along the skull.

So it now got to the brain (well unless you rolled a 1 on damage). Once there you ignore that pi- injury multiplier as any thing at thsi point gets a x4 injury multiplier due to being inside the skull. so the range is now 4-20pts of injury in 4pt incremental steps, (so 4, 8, 12, 16 & 20).

But before we apply that injury to HP we get the knockdown effect. Any skull hit that cause any injury will require a HT roll avoid being knocked down and stunned, if you fail that roll by 5 you will not only be knocked down and stunned but unconscious. Here's the thing a major injury to the skull will penalise that roll by a whopping -10. What that means is if were talking a 4pt injury it's a straight HT roll to avoid knockdown, but at 8pts or more it's a -10 to the roll and your likely to be unconscious not just knocked down/stunned.


Right so lets apply the injury 4pt is not so bad. Maybe the bullet didn't penetrate that far past the skull, maybe is travelled along the inside curve of the skull (this has happened)

8pt is a major wound, that's getting you -10 penalty on your knockdown test.

12pt has you at negative so even if the dissident somehow stayed concious he rolling every second to remain so if he acting.

16pts pretty much the same as 12pts (but see below)

20pt that's death roll time, he fails a HT roll and he's dead straight away. (50% chance, depning if you use mortal wounds)

So at this point you can see a pretty wide range of immediate effects (although most involve high likelihood of dropping to the floor unconscious) This makes sense because that scenario you described of the bullet bouncing around the brain like a pinball is not a guaranteed one but just one possible behaviour in that situation. It's also factor of bullet energy, and well .22LR just doesn't have that much energy.

Also please note baring massive trauma to certain bits of the brain instant death is a quite hard to inflict in real life (but again see below for instant death vs. delayed death)


So now we come to ongoing effects of the injury, this is what likely kills him in the end.

If your using the optional more realistic wound rules from Martial arts the dissident will bleed a -1 for each 5 points of injury, and because it inside the skull it's a test every 30 seconds and first aid is no use you need surgery to stop it. (not that treatment is on the cards in this scenario anyway)

So that will bleeding rolls at -1 if it's an 8pt injury, -2 if it's 12pts, -3 if its 16pts and -4 if it's 20pts. For the bleeding to stop by itself you need three successes in a row (or a critical)

Executions are a messy and sometimes uncertain business, even back of the head KGB style. This is why they tend not to rely on a single bullet.


If you really want to read up on this there are some quite detailed descriptions of the Katyn executions by the NKVD in 1940 floating about.

Long story short a bullet to your target's head will stop them moving very quickly in GURPS but that is not the same as instantly dead. But for them to survive the experience they will need to be lucky:

1. You rolled low damage,
2. They rolled well on subsequent bleeding tests,
3. They made it to surgery before bleeding out.

Or a mix of all three of course

But 2+ bullets even from .22Lr will get you there pretty quickly though. The thing is unless your KGB killer is going to check for pulse and breathing afters shooting his target "you shoot him in the head he drops unconscious to the ground immediately and all brain activity ceases soon after" is functionally the same as "you shoot him in the head and he dies"

*shape being a big factor

Last edited by Tomsdad; 04-02-2016 at 12:38 AM.
Tomsdad is online now   Reply With Quote
Old 04-01-2016, 01:40 AM   #9
Polydamas
 
Join Date: Jan 2006
Location: Central Europe
Default Re: Bullets: Overpenetration, Tumbling, Traveling

One thing to remember is that firearm stats in GURPS are based on penetration of steel plate, which is pretty well understood. That base damage is them modified with a Wound Channel Modifier, hit location multipliers, bleeding, etc. to represent how some rounds with roughly equal penetration tend to have different effects on the target. As others have said, wounding is a topic which gun bunnies argue about a lot, but is not well-enough understood for everyone to agree on a simple model (and any replacement for the current core rules would have to be no more complicated, take no more time, and require no more background knowledge).

Aside from Doug's explanation of his model, the Pyramid article "Survivable Guns" and the "My Carbine Sucks!" sidebar in GURPS Tactical Shooting are also relevant.

Quote:
Originally Posted by FF_Ninja View Post
I'm envisioning a situation where, say, a Russian agent with a .22LR pistol pops someone dissident the skull (old KGB style), and the round penetrates only the first layer of bone but then proceeds to tumble and travel, turning said dissident's brains into scrambled eggs. A through-and-through shot from a heavier caliber weapon wouldn't do that.
Executions are an excellent example of the kind of situation where its best not to roll damage, since the damage rules are designed for combat. A common house rule is to give executioners who can set up the situation correctly (and maybe make a skill roll) an automatic high-damage critical hit (see Low Tech, I think).
__________________
"It is easier to banish a habit of thought than a piece of knowledge." H. Beam Piper
Polydamas is offline   Reply With Quote
Old 04-01-2016, 02:51 AM   #10
Tomsdad
 
Join Date: Jan 2010
Location: Brighton
Default Re: Bullets: Overpenetration, Tumbling, Traveling

Right given my last post was long one I thought I'd split few things off.

.22LR really isn't good execution round through the skull. Your cold war era KGB executer is more likely to be using something like the Izhmekh PM, 9x18mm Makarov at 2d pi and an average hit on the dissident's skull is a HT roll vs. instant death. It has roughly the same velocity but more mass and is a more energetic round then the .22LR.


Skull hits and through and though. Right OK yes obviously a fast/energetic enough round will go all the way through a skull and out the other side.

However skull hits is one of the few areas were hydrostatic pressure is actually a significant aspect of damage in the human body. Soft tissue contained within a hard, rigid case. Any bullet that has enough energy to go in through and out a skull will also put a lot of energy into the brain. The brain is not very resistant to that energy, and we are not very resistant to damage to our brains. So yes larger more energetic bullet going all the way through (and not fragmenting or rebounding around) is very capable of scrambling the brain due to this, and thus killing us. The softness of brain tissue and lack of hard objects within the brain also reduce chances for fragmentation


But obviously in same cases bullet travel through and out the body having failed to leave all their energy inside. This is covered by over penetration rules*. These rules don't apply to vitals, skull, veins & arteries and neck hits. Generally because damage to these areas are pretty serious and not just about wound channel size. But again the actual game effects are a mix of different knockdown penalties, location wound multipliers and penalties to bleeding. for instance as above the skull/brain comes with x4 injury multiplier that replaced the attacks injury mod. Veins & arteries add another 0.5 to weapons injury mod, but come with an extra -3 or -4 on bleeding, etc, etc.


Your basic point about larger bullets don't do more damage then smaller ones, is really too abstract to accept. It's subject to so many variables. Yes a .22 through the eye will do more damage than .45 through the hand, but which is the deciding factor the bullet diameter or wound location? (this is obviously an extreme comparison, but really you'll find variables in most comparisons).

Out of roughly similar hand guns the faster but smaller 9mm (2d+2 pi) will penetrate further but leave a smaller wound channel (pi) than the larger slower .45 (2d pi+)

Just on those ratings on average they are pretty equal the 9mm will do average a 9pt injury, the .45 will do 10pt.

But which is better will depend on the specific situation more than just those ratings. (EDIT: Just to quickly point out I consider the 9mm vs .45 to be closer comparison than the .22 to either of these)
*and by reducing injury mods, having an armour divisor etc.

Last edited by Tomsdad; 04-03-2016 at 12:43 AM.
Tomsdad is online now   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Fnords are Off
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 09:27 AM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2020, vBulletin Solutions, Inc.