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Weapon Penetration


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I've started playing Darklands again, and it's inspired me to try to work out a penetration mechanic for my BRP games. The aim for my house rules have always been "as realistic as practical". I tend to run games with a grittier atmosphere where people die quickly and messily if they don't find cover or wear armor, depending on the setting.

I think an elegantly done penetration mechanic would add realism without much more in the way of bookkeeping. Has anyone added penetration to fantasy/historical systems in there house rules? Has anyone published something that addresses this?

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Some of the newer BRP supplements use the weapon damage rating like a PEN score. If the damage exceeds the AP the target takes full damage. This reflect the fact that the damage progression is not really linear. That is one round from a 120mm cannon (20D6) has much greater penetration, and hits a lot harder than twenty rounds from a light pistols (1D6, rolled twenty times).

The idea of a PEN stat has some merit, but it would require working out a correlation being AP and armor thickness. You'd have to rework all the weapon damage stats, too.

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My old Striker! conversion uses PEN in this way: Striker! Sidearms - Downloads - Basic Roleplaying Central.

It's actually pretty simple, as 25+ years of use have verified. But I'm not sure it's really needed for fantasy/historical weapons and armour - you don't really get the kinds of weapons that penetrate armour to the same degree as modern firearms.

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I've started playing Darklands again, and it's inspired me to try to work out a penetration mechanic for my BRP games. The aim for my house rules have always been "as realistic as practical". I tend to run games with a grittier atmosphere where people die quickly and messily if they don't find cover or wear armor, depending on the setting.

I think an elegantly done penetration mechanic would add realism without much more in the way of bookkeeping. Has anyone added penetration to fantasy/historical systems in there house rules? Has anyone published something that addresses this?

I seem to remember that Rubble and Ruin:

Basic Roleplaying Central - RUBBLE & RUIN - A World Gone Mad with Killing

Had penetration rules for firearms as well

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Chaosium 2111 Rogue mistress stormbringer adventure ,had some weapons like pistols that gave penetration values .

at one time i had penetration values for many weapons also recoil values. it does get a bit complicated, if you add penetration values then you sometimes have to lower the damage dice. I never realy found a effective version myself. you could try to convert the penetration values from twilight 2000 2nd edition, but i am not sure if that would be worth the trouble. i think probally the striker side arms mentioned above from traveler or even a conversion of mega-traveller would be the best route.

Edited by skull
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DO any of those systems have guidelines to tell you how much protection (in AP) provided by a given thickness of armor? Or how to determine the PEN value for a weapon?

I'm not thinking about personal armor as much as about cover provided by walls, vehicles and such. For instance, if somebody is inside an APC and the APC gets sprayed by a 7.62mm Machine gun, can the bullets penetrate? That sort of thing.

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How I do it...

Weapons have a straight damage causing capability (the dice rolled).

Armor has a straight armoring capability which reduces or eliminates damage from the incoming attack.

Damage that is stopped may still cause blunt trauma to the target.

Ammunition can make weapons penetrate armor better (such as AP rounds) or worse (such as glaser safety slugs, reverse wadcutter, etc.)

The rationale is that weapons start off with a set amount of energy, and the more stuff it penetrates, it has to expend energy to get through it, thus leaving less energy to damage the target. Granted, this is gross oversimplification of wounding mechanisms, but for games it is good enough.

Not having a copy of the game you refer to in the OP, my benchmarks for damage are:

1" of penetration in flesh = 1 point of damage

1 mm of Iron = 1 point of damage

0.5mm of RHA = 1 point of damage

I have a pretty long list of weapon damages and armor types that I can PM you if wish.

-STS

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Just a thought: weapon penetration is shown by the number of dice one would roll for damage, e.g. 2d6 would ignore 2 points of armor. If a player wants to use AP rounds, he couls roll a higher number of dice, but is not allowed to exceed the max amount of damage - in fact he also loses all "hard" damage modifiers. So a 2d6+2 could dor 3d4 points of damage AP. a 1d10+1 my roll 2d4.

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Just a thought: weapon penetration is shown by the number of dice one would roll for damage, e.g. 2d6 would ignore 2 points of armor. If a player wants to use AP rounds, he couls roll a higher number of dice, but is not allowed to exceed the max amount of damage - in fact he also loses all "hard" damage modifiers. So a 2d6+2 could dor 3d4 points of damage AP. a 1d10+1 my roll 2d4.

Nice theory, but bad in practice. Using your example, of a 2D6+2 rifle going to 3D4, you can see that the character would have been better off not using AP ammo. 2D6+2 would have better PEN and damage than 3D4. Same with the 1D10+1 vs. 2D4. I think you got a good idea here, but you have to fiddle with the numbers a bit. The basic concept, improving PEN at the cost of lowering damage is good.

Maybe dropping the die size, keeping the add, and using the min. roll as the PEN? FOr example, an AP round for a 2D6+2 rifle would do 2D4+2, and have a PEN of 4. The 4 PEN would hake the round slightly better (2 points) against armor, but do less damage (7 vs. 9) on average, and have a lower max (10 vs 14).

Hollow Points could be done by reversing the process. You bump up the dice, but double any AP up to the min. damage rolled. So a HP round for a 2D+2 rifle would do 2D8+2, but double the first 4 points of Armor.

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The risk system from Rubble and Ruin is, as said above, basically the same idea as penetration. AND... you can download the system for free in the download section: Modern_Firearms - Downloads - Basic Roleplaying Central.

With firearms, in our "real" world armor is generally all or none -- not additive as represented with the Armor Point concept. Risk is my answer to this issue.

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Thanks rleduc, the risk system looks pretty good. I have some questions though.

1) You say that the armor is all or none, but the rules say that if the damage beats the protection, the risk is dropped one level (about a point). Which is it?

2) What method di you use to arrive at the risk vales for the weapons, and the protection value for the armors? Did you base risk on energy, energy over area, momentum? Or did you just "eyeball it" I'd like to know so I can get an idea of how to come up with ratings for other weapons and armors. For example if I wanted to add in a Russian 14mm MG, or a Cassul .454 how would I do so? Or what would the protection value be for an M113 APC? I'm just wondering if you used some method that can be applied universally.

THe risk system looks really good, and could help me to solve some of the difficluties I'm having with vehicles and weapons in BRP terms, if it can be expanded to accommodate other weapons and armor.

It looks like an energy/area method.

Edited by Atgxtg
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The risk system from Rubble and Ruin is, as said above, basically the same idea as penetration. AND... you can download the system for free in the download section: Modern_Firearms - Downloads - Basic Roleplaying Central.

With firearms, in our "real" world armor is generally all or none -- not additive as represented with the Armor Point concept. Risk is my answer to this issue.

Some interesting ideas, the risk factor reminds me of BDG (Bullet Damage Group) from FGUs Aftermath but with a bit more variation (BDG simply used d10s, so there were big jumps when you crossed a threshold).

I am a bit unsure of your claim armor is all or nothing, I've never seen anything to suggest that, can you point me to a source?

I do know when you get into large caliber projectiles (tank rounds) there is a good chance the incoming round will shatter instead of penetrating if it issmaller than the armor is thick (75mm round hitting 100mm of armor), which is where the idea of capped rounds (APC) developed during WW2 (protected the penetrator from the initial shock) but I've never seen that applied to soft armor/cover, only hard armor plate.

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I am a bit unsure of your claim armor is all or nothing, I've never seen anything to suggest that, can you point me to a source?

I'm not rheduc, but I think I know the answer to this. It's not a real world issue but an RPG specific one. Damage in BRP is not linear, that is a weapon that does 2D6 is really more that twice as powerful as one that does 1D6. For example a 120mm round (20D6) is more than 20 times more deadly that a 25mm pistol round (1D6). A typical rifle bullet has 3.5-5 times the energy and around twice the penetrating power of a 9mm pistol round. So if a rifle bullet hits a vest designed to stop 9 mm rounds, it still has 2-5 times the energy of a 9 mil left over after the vest. In BRP terms that means that the round should still do more damage than the 9mm.

Since each point of damage is a percentage increase of the previous value, as the damage goes up the value of what is left over increases dramatically.

Whith large cailber stuff, it gets more complicated, since there are things like spauling to consider.

I do know when you get into large caliber projectiles (tank rounds) there is a good chance the incoming round will shatter instead of penetrating if it issmaller than the armor is thick (75mm round hitting 100mm of armor), which is where the idea of capped rounds (APC) developed during WW2 (protected the penetrator from the initial shock) but I've never seen that applied to soft armor/cover, only hard armor plate.

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Thanks for the input guys! I think I'm going to be doing something similar to what Nick and Vile have said about - the PEN score showing how many AP get ignored by the weapon. I'll see if I can get something posted in the next couple of weeks.

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Thanks for the input guys! I think I'm going to be doing something similar to what Nick and Vile have said about - the PEN score showing how many AP get ignored by the weapon. I'll see if I can get something posted in the next couple of weeks.

That's what I am planning to use for Legend:SciFi, if I ever get back to working on it.

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Thanks rleduc, the risk system looks pretty good. I have some questions though.

1) You say that the armor is all or none, but the rules say that if the damage beats the protection, the risk is dropped one level (about a point). Which is it?

2) What method di you use to arrive at the risk vales for the weapons, and the protection value for the armors? Did you base risk on energy, energy over area, momentum? Or did you just "eyeball it" I'd like to know so I can get an idea of how to come up with ratings for other weapons and armors. For example if I wanted to add in a Russian 14mm MG, or a Cassul .454 how would I do so? Or what would the protection value be for an M113 APC? I'm just wondering if you used some method that can be applied universally.

THe risk system looks really good, and could help me to solve some of the difficluties I'm having with vehicles and weapons in BRP terms, if it can be expanded to accommodate other weapons and armor.

It looks like an energy/area method.

Sorry for my tardy reply. For number 1, if Risk of attack is greater than Risk "protected by armor" then attack risk is droped by one. I hit you with Risk 11 weapon, and you have Risk 10 or less of protection then you take damage from a Risk 11-1 attack. (Of course other modifiers may apply.)

For question number 2, I used a totally geek-aligned system (explained in the Firearms download, but not in the R&R monograph). What I did was to use a non-linear regression on "typical" muzzle energy versus the average damage listed in the Big BRP book. I then used that relationship to calculate Risk for other rounds (with a few asides listed in the download document -- particularly I am giving each calibur a "typical" energy and then individual firearms can raise or lower the Risk of the calibur -- it is just a gaming expedient).

For the record, in play the system goes very quickly and give a first-blush approximation of modern firearms damage. The reason I used the muzzle energy instead of other metrics is because I can get those values easily from gun magizines and the Shooter's Bible. This gives me a system that will accept a large number of modern firearms without a lot of work.

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Some interesting ideas, the risk factor reminds me of BDG (Bullet Damage Group) from FGUs Aftermath but with a bit more variation (BDG simply used d10s, so there were big jumps when you crossed a threshold).

I am a bit unsure of your claim armor is all or nothing, I've never seen anything to suggest that, can you point me to a source?

For the record, R&R started life in the 1980's as a series of Aftermath games... BDG was certainly on my mind when I developed the Risk system (as was e-values from Morrow Project).

The all or none property of ballistic armor comes from gel studies. I'll see if I can find an original source -- the idea is to use a fixed round and energy and then fire it into increasing thickness of Kevlar, while measuring penitration depth. The response is sigmodial with a very step rise from near-zero to near-final penitration. I modelled this as square response...

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Sorry for my tardy reply.

Thaks for the reply. I don't mind waiting a bit.

For question number 2, I used a totally geek-aligned system (explained in the Firearms download, but not in the R&R monograph). What I did was to use a non-linear regression on "typical" muzzle energy versus the average damage listed in the Big BRP book. I then used that relationship to calculate Risk for other rounds (with a few asides listed in the download document -- particularly I am giving each calibur a "typical" energy and then individual firearms can raise or lower the Risk of the calibur -- it is just a gaming expedient).

For the record, in play the system goes very quickly and give a first-blush approximation of modern firearms damage. The reason I used the muzzle energy instead of other metrics is because I can get those values easily from gun magizines and the Shooter's Bible. This gives me a system that will accept a large number of modern firearms without a lot of work.

Understood. I am/have been working on a vehivcle desing system for BRP and have used formulas for determining some game values for the same reasons. It's easier to stat out large numbers of things, and do so in a consistently that way. I've got some spreadsheets that automate the process with hundreds of cars and other vehicles.

I don't suppose you could let me know what progression you used for armor? I've been using AP=log(mm)*20, lately, which matched up with the 1 inch plate=28AP from the BRP core book, and gives about a +6 AP per doubling of thickness, but I'd be willing to adjust that if somebody has something better.

BTW, your non-linerar regression method gives results fairlysimilar to EABA. Most risk rating are within a point or so of the EABA damage ratings.

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  • 2 weeks later...

For question number 2, I used a totally geek-aligned system (explained in the Firearms download, but not in the R&R monograph). What I did was to use a non-linear regression on "typical" muzzle energy versus the average damage listed in the Big BRP book. I then used that relationship to calculate Risk for other rounds (with a few asides listed in the download document -- particularly I am giving each calibur a "typical" energy and then individual firearms can raise or lower the Risk of the calibur -- it is just a gaming expedient).

Sorry for my lack of perspicacity! I just noticed the formula at the end of the Firearms Document. I missed it before. I thought there were just weapon tables at the end. Thanks for providing the details-sorry I was too dense to notice it before.:o

Are the vales for Risk 16 (2D10) and 17 (2D6) reversed? The doc says that average and max risk never go down, but they do here.

BTW, any idea for expanding the table beyond Risk 20?

Edited by Atgxtg
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