Combining and Layering Flexible Armor Against Firearms

[General Lee]

Originally Posted by DanHoward

It might be simpler to simply subtract one die per layer.

First layer gets full value
Second layers gets -1 die
Third layer gets -2 dice
etc.

The result would be that lighter layers effectively contribute nothing extra.

The bottom line of all this is turn more impracticable to munchkins abuse of layering soft armor. But the core rules already have a certain degree of simplification, so subtracting -1 die per layer, despite much appealable to me, is yet another degree of oversimplification.

I confess that I prefer approaches that mirror more realistically, despite a tick more complexity, but nothing too “heavy” to slow-down the game.

[Anthony]

Note that fundamentally, the rounds level IIIa are supposed to stop have a total energy of 12-15J/mm^2, while the rounds level III is supposed to stop have a total energy of ~75J/mm^2, and the protection for flexible armor is fairly linear in thickness.

[General Lee]

Originally Posted by Anthony

Note that fundamentally, the rounds level IIIa are supposed to stop have a total energy of 12-15J/mm^2, while the rounds level III is supposed to stop have a total energy of ~75J/mm^2, and the protection for flexible armor is fairly linear in thickness.

But level III armor is not of the hard type, just being ceramic, or plastic plates, or solid iron? So, not “soft” armor?

Still, this kind of information makes me uncomfortable to state that one additional layer of, say, level IIIa armor, would give the same “protection” than a additional layer of a level II armor.

[Anthony]

Originally Posted by General Lee

But level III armor is not of the hard type, just being ceramic, or plastic plates, or solid iron? So, not “soft” armor?

Level III is hard armor, but the main point is that you'd actually expect a rifle to shoot through around five level IIIa vests.

[General Lee]

Originally Posted by Anthony

Level III is hard armor, but the main point is that you'd actually expect a rifle to shoot through around five level IIIa vests.

Not five layers. Definitely no. Actually, five layers would have stopped a 5d attack most of the times using Armor as Dice, the DR/3 solution, and even in the example of the article (IIa+IIIa+IIIa+IIIa), if it had one additional layer.

The point is that combined in layers of soft armor, did not work against firearms, realistically, as stated in core rules. So how to better represent that realistically? That what I was looking for.

Eventually, stacking soft armor would stop rifle rounds, but that would be awkward, cumbersome, and heavy. Still, it happened before, and I maybe could use it in the future in one of my sessions.

I think we are in the same page here, not in crash route.

[Tomsdad]

Originally Posted by General Lee

No sorry needed here. You helped me a lot. Thanks.

Cheers!

Originally Posted by General Lee

Not five layers. Definitely no. Actually, five layers would have stopped a 5d attack most of the times using Armor as Dice, the DR/3 solution, and even in the example of the article (IIa+IIIa+IIIa+IIIa), if it had one additional layer.

The point is that combined in layers of soft armor, did not work against firearms, realistically, as stated in core rules. So how to better represent that realistically? That what I was looking for.

Eventually, stacking soft armor would stop rifle rounds, but that would be awkward, cumbersome, and heavy. Still, it happened before, and I maybe could use it in the future in one of my sessions.

I think we are in the same page here, not in crash route.

Just to say the (IIa+IIIa+IIIa+IIIa+IIIa) wouldn't stop 5d as per the article, its:

Armour as Dice 5d vs. (2d+1)+(3d+2)+(3d+2)+(3d+2)+(3d+2) turns into

Flexible armour 5d vs. (2+3+3+3+3)

5d - 14 = 1d

don't get me wrong not massive penetration by any means. One more IIIa vest would stop it though.


But if you want to further penalise stacking, DanHowards suggestion of -1 dice per layer in combination here would certainly give you that

it would be (2d+1)+(2d+2)*+(1d+2)+(0d+2)+(0d+2) = 5d-5 = 3d+2

In fact it simplifies the calculation because you can just ignore the layers past the number of dice in the highest rated layer. In the case above only three layers matter, you could safely ignore the 4th & 5th layers.

It does mean in theory that 20, 100 or 1,000 kevlar vests won't stop the round, but really this is already fringe to begin with before we start worrying about '100 vests' so IMO it doesn't matter.


But if you really want to discourage munchkins doing this enforce the -DX penalty rules for additional layers (IME there's nothing munchkins hate more than being less awesome).

Thing is with all this he doesn't need to wear 5 layers of vest here, he could just wear one layer with a trauma plate in.

It's going to be lighter, cheaper, and considerably more effective at stopping a rifle, and less annoying than 5x vests



*not quite sure how it would apply in mixed stacks but either way we're only talking the difference of 1-2 points here

[Tyneras]

How do your calculations work out if you factor in the 1.3 to 1.7 armor divisors a lot of modern bullets would have? I recall a lot of the more detailed ballistics models for GURPS include them in calculations of penetration.

[Tomsdad]

Originally Posted by Tyneras

How do your calculations work out if you factor in the 1.3 to 1.7 armor divisors a lot of modern bullets would have? I recall a lot of the more detailed ballistics models for GURPS include them in calculations of penetration.

Would they necessarily apply to a rifle bullet at 1872fps? (they may well it's a genuine question on my part not a rhetorical one)

But either way if they do you are get better penetration. Although if you go with the rules for flexible armour from "Gaming Ballistic" it's going to come down to thresholds and how you convert the amended DR to dice and pluses.

[Varyon]

Originally Posted by Tyneras

How do your calculations work out if you factor in the 1.3 to 1.7 armor divisors a lot of modern bullets would have? I recall a lot of the more detailed ballistics models for GURPS include them in calculations of penetration.

The GURPS stats are basically "How much RHA steel will this weapon punch through?" When you end up with something that should have an armor divisor in that range, the GURPS stats are typically going to get penetration right but overestimate wounding. As I believe was noted earlier in the thread, Armor Divisor and Wounding Modifier are really just different ways of saying the same thing - a 1d(2) pi attack and a 2d pi- attack are functionally the same thing*. 5d(1.6) pi would probably show up in the book as 8d pi, not as 5d.

*Well, unless using the common houserule of capping penetrating damage at HP or similar (the version in HT caps injury, and thus makes there be no difference between those two attacks).

[Ulzgoroth]

Originally Posted by Varyon

The GURPS stats are basically "How much RHA steel will this weapon punch through?" When you end up with something that should have an armor divisor in that range, the GURPS stats are typically going to get penetration right but overestimate wounding. As I believe was noted earlier in the thread, Armor Divisor and Wounding Modifier are really just different ways of saying the same thing - a 1d(2) pi attack and a 2d pi- attack are functionally the same thing*. 5d(1.6) pi would probably show up in the book as 8d pi, not as 5d.

*Well, unless using the common houserule of capping penetrating damage at HP or similar (the version in HT caps injury, and thus makes there be no difference between those two attacks).

There's a RAW difference, actually: Hardened DR halves the penetration of 1d(2) but has no effect on 2d.