01-07-2017, 04:28 AM | #1 |
Join Date: Jan 2008
Location: Somewhere between Cape Horn and Zenith Point
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Combining and Layering Flexible Armor Against Firearms
Hi everyone!
I was reading this when I decided to check how gurps would deal it - yeah, I did not have it by rote. By the rules in Basic Set: Characters, 4ed, p. 286 armor could be combined in layers, if inner layers are flexible and concealable, adding DR from each other, with penalty of -1 per layer added. So, in the example explained there, the armor combined (NIJ Ratings IIA+IIIA+~IIIA+~IIIA) would have ~DR 44, tested against a .300 AAC Sellier & Bellot 147 gr FMJ cartridge shot by an AR Rifle -- with muzzle energy roughly equal to "a 7.62x51mm M80 FMJ fired from an M14 at about 400 yards", by which for GURPS means nothing because 400 yards is below half-damage range --, which I estimated it doing 5d+2 of damage (or 20 Hit Points on average), and clearly it fails to protect a wannabe wearer of this armor. Why? How come 20 Hit Points could blowthough an armor with ~DR44? My immediate answer to that -- IT COULDN'T, according to the rules as it is. So I come up with this House Rule, against firearms only, layering soft armor would add only 20% of the original DR layer, round down, added to the highest layer DR. So, in the example above, the armor combined would have DR17, easy to a .300BLK, or any other rifle-powered cartridges, to overcome. So, any ideas, is this the right direction, any comments, would you do it differently? Thanks in advance. Last edited by General Lee; 01-07-2017 at 04:37 AM. |
01-07-2017, 07:10 AM | #2 |
Join Date: Nov 2015
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Re: Combining and Layering Flexible Armor Against Firearms
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01-07-2017, 07:58 AM | #3 |
Join Date: Aug 2010
Location: The Land of Enchantment
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Re: Combining and Layering Flexible Armor Against Firearms
My response is that calling the two IBA groin panels "level IIIA" is probably optimistic. I'd look into that a bit, first. But generally, yeah, soft armor is not meant to stop rifle bullets.
GURPS is a model, and to be playable it cannot be comprehensive to reality. If it were, what you'd have is some sort of AI reality simulation, and one combat second would take 32 years to play out. So there are going to be corners where it fails spectacularly. (Another is attacks against some structures and ships, which are WAY too easy to destroy in GURPS. There are others.) I'd wager that someone wearing four sets of Point Blank were not considered in the playtest.
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I'd need to get a grant and go shoot a thousand goats to figure it out. Last edited by acrosome; 01-07-2017 at 08:03 AM. |
01-07-2017, 08:08 AM | #4 |
Join Date: Jun 2013
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Re: Combining and Layering Flexible Armor Against Firearms
From what I understand, penetrated armor protects much less than GURPS suggests. A simplified version is that the square of armor protects against the square of damage - so if those armors were, say, DR 8, 12, 12, and 12, that's not DR 44, it's DR (64+144+144+144)^(1/2)=22, which still should have been enough to stop the 20 damage of the shot - it's possible our DR values are off, or the damage is off. A gameable version of this rule is to state that, if damage is greater than DR, divide DR by 3 to determine how much it reduces damage by. Above, we'll round that DR 8 up to DR 9, in which case the first layer is penetrated (17 damage remaining of our 20), as is the second (13 remains) and third (9 remains), but the fourth is enough to stop the bullet. Something is definitely off, particularly with the fact that the bullet apparently had enough chutzpah left to punch through an estimated 20 inches of flesh - which works out to right around 20 damage on its own (flesh is roughly DR 1/inch). That implies that, if the bullet can get through soft armor, it outright ignores it, rather than just reducing it via a difference of squares approach (or the simplified divide by 3 method, which tends to give very similar results). That, or the bullet in question has some sort of armor divisor to it.
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01-10-2017, 11:39 AM | #5 |
Join Date: Oct 2008
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Re: Combining and Layering Flexible Armor Against Firearms
Soft ballistic armor works a lot different in real life than in Gurps. In Gurps armor reduces damage by a given value and thus the object on the other side takes less damage. In real life soft ballistic armor that fails to stop a projectile will tend to "catastrophically fail" at the location of the penetration and not slow down the projectile much thus it would hit a second such panel with most of it's energy left. Only if the penetration is really marginal can we see a large slowdown but penetration like the Gurps armor model.
To model the real behavior Gurps you would need to give such armors a fairly high "penetration value"(PW) and really low(or no) DR. The PW would then be compared to the damage and if damage was less then no penetration happens and blunt trauma is applied. If the damage was more then only the minor DR is applied and the resulting damage is applied to the object protected or inner layer armor. If doing such penetration value thing it would likely make mostly sense to use armor as dice type thing for the PWs and express them in dice of damage and not damage values. |
01-10-2017, 12:06 PM | #6 | ||
Join Date: Jan 2008
Location: Somewhere between Cape Horn and Zenith Point
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Re: Combining and Layering Flexible Armor Against Firearms
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Your approach is appealing, still it not answers what happen. I was wondering if the armor used in the “test” were in good shape, i.e., could have its performance degraded by lower HT? |
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01-10-2017, 12:24 PM | #7 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: Combining and Layering Flexible Armor Against Firearms
The problem with the GURPS damage model is that it's trying to use a single DR value for multiple different armor and weapon types. This is an understandable simplification, anything realistic is going to be hell of complicated, but it means you get anomalies. Notably, flexible armor has somewhat different thickness scaling than hard armor, and also has variable protection with projectile velocity. A truly realistic assertion for the protection of level IIIa armor is that it stops the attacks it's rated as stopping, and no reliable statements can be made about its performance against other attacks.
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01-10-2017, 06:48 PM | #8 | ||
Join Date: Jan 2008
Location: Somewhere between Cape Horn and Zenith Point
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Re: Combining and Layering Flexible Armor Against Firearms
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All that for sake of playability with a sense more accurate sense of reality, instead of ruling that “as this situation is beyond the curve of the system, I blinded myself and accept in play an unrealistic result”. |
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01-10-2017, 07:09 PM | #9 | |
Join Date: Jan 2008
Location: Somewhere between Cape Horn and Zenith Point
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Re: Combining and Layering Flexible Armor Against Firearms
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Maximun damage could happen in critical hits or pure luck in dice, but it could not be considered as for rating armor. In Adjusting Damage, GURPS High Tech 4ed., p.166, the first step is multiply damage dice by 3.5, retaining fractions, and add the damage bonus or penalty, before apply any modifier due to upgrades or options. Also, look this blog by HANS, it could help explain why I estimated damage this way. The example is in the link that I post it, not in the p. 286. Sorry if I was not clearer before. |
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01-10-2017, 07:50 PM | #10 | |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: Combining and Layering Flexible Armor Against Firearms
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Tags |
flexible armor, high-tech, layering armor |
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