Combining and Layering Flexible Armor Against Firearms

[Tomsdad]

There is a way you can do this by GURPS (or more precisely by Douglas Cole's rules for armour as dice and his further rules for kevlar style flexible armour here)

The round is 5d

IIIa = 12DR which in armour as dice is 3d+2

Now normally in armour as dice if you put 4x layers of 3d+2 up against 5d the 5d will be stopped dead (by the 2nd layer), pretty much the same as the normal GURPS DR rules.


But if you take the rules tweak for kevlar type armours each layer of 3d+2 Kevlar will subtract 3 points from DR not 3d+2.

So against 4 layers of DR12 Kevlar you'd end up with 5d-12 = 2d-2*

Now to save time I just multiplied the effect of the first layer by the number of layers. You could run it one at a time, (you might get different results due to several instances of rounding)


But basically:

Originally Posted by acrosome

... I'd wager that someone wearing four sets of Point Blank were not considered in the playtest.

Is a key point here.


*now maybe that's not 6" of ballistic gel and 4x milk cartons, but it's still a significant wound. But if we're saying those panels don't qualify as DR12 and 3d+2 (and some here seem to be) but are maybe less protective enough to end up as 2d+x in this system than you'll be left with more penetration. IIa is DR8 = 2d+1 for instance.

Actually since it's DR8+ DR12+DR12+DR12 so (2d+1)+(3d+2)+(3d+2)+(3d+2) you'd be left with 5d-11 = 2d-1 penetration

[Tomsdad]

Another way to do it is the way the old CP2020 rules worked for layering flexible armour.
Instead of just summing all the layers, the first layer got full value but subsequent layers just gave a relatively small bonus depending on how close they were to the value of the first layer.

[Tomsdad]

One other thing watching that chaps video he records 1872 fps

which on a 147gr bullet comes out at 1551j so that's 5d-1 I think according to the reloaded chart (not a big difference, and one that can easily be a rounding difference but since he gave the actual recorded speed)

[General Lee]

Originally Posted by Tomsdad

There is a way you can do this by GURPS (or more precisely by Douglas Cole's rules for armour as dice and his further rules for kevlar style flexible armour here)

The round is 5d

IIIa = 12DR which in armour as dice is 3d+2

Now normally in armour as dice if you put 4x layers of 3d+2 up against 5d the 5d will be stopped dead (by the 2nd layer), pretty much the same as the normal GURPS DR rules.


But if you take the rules tweak for kevlar type armours each layer of 3d+2 Kevlar will subtract 3 points from DR not 3d+2.

So against 4 layers of DR12 Kevlar you'd end up with 5d-12 = 2d-2*

Now to save time I just multiplied the effect of the first layer by the number of layers. You could run it one at a time, (you might get different results due to several instances of rounding)



*now maybe that's not 6" of ballistic gel and 4x milk cartons, but it's still a significant wound. But if we're saying those panels don't qualify as DR12 and 3d+2 (and some here seem to be) but are maybe less protective enough to end up as 2d+x in this system than you'll be left with more penetration. IIa is DR8 = 2d+1 for instance.

Actually since it's DR8+ DR12+DR12+DR12 so (2d+1)+(3d+2)+(3d+2)+(3d+2) you'd be left with 5d-11 = 2d-1 penatration

A good point to work with. I just don't want to go with "Armor as Dice", but with the Kevlar style rule by Douglas Cole you mentioned, I am very inclined to adopted it in the future. Its more simple (for a PC point of view, at least, not so true for GMs that have to do a litle math before sessions) than tweaking in mid-game.

Originally Posted by Tomsdad

Another way to do it is the way the old CP2020 rules worked for layering flexible armour.
Instead of just summing all the layers, the first layer got full value but subsequent layers just gave a relatively small bonus depending on how close they were to the value of the first layer.

Unbeknownst to me, I came up with a similar proposition in the beginning of the thread.

[Tomsdad]

Originally Posted by General Lee

A good point to work with. I just don't want to go with "Armor as Dice", but with the Kevlar style rule by Douglas Cole you mentioned, I am very inclined to adopted it in the future. Its more simple (for a PC point of view, at least, not so true for GMs that have to do a litle math before sessions) than tweaking in mid-game.

I don't run a lot of modern day stuff, but I'm a bit a recent convert to armour as dice. It actually runs quite quick in play I find. It might just be me but I find it quicker to subtract a number from a gun's damage code and roll a smaller number of dice, than roll a larger number of dice.

Originally Posted by General Lee

Unbeknownst to me, I came up with a similar proposition in the beginning of the thread.

Yeah sorry you did

[General Lee]

Originally Posted by Tomsdad

Yeah sorry you did

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

[General Lee]

Originally Posted by Varyon

(...) 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. (...).

What if we consider that if the damage rolled is superior of the DR of the layers, considered separately, then the DR of the layers combined would be the sum of the DR/3 of all layers?

I do some testing with this rule and I think it works very well for me. Considering that soft armor encountered nowadays would have DR ranging from 6 to 16 (DR 6-16), using the rule above, each layer will present only 2-5 DR.

So, in the example, (IIa+IIIa+IIIa+IIIa) against .300 AAC BLK (5d, or 18 Hit Points on average), all layers have inferior DR than the damage rolled, so the rule kick in, giving a combined DR of 14 (IIa[DR2] + IIIa[DR4] + IIIa[DR4] + IIIa[DR4]).

Thence, the wearer of this combo-armor would have 4 Points of Basic Damage. Close to the 2d-1 of penetration achieved [actually 33% less of penetration on average], using armor as dice rule as described in Tomsdad post.

[Dustin]

Another approach to reduce the effectiveness of the extra layers could be to give the best layer its full DR, second gets half, third gets one-third, etc. So for the example of DR 8, 12, 12, and 12, it would add up to:

12 + 12/2 + 12/3 + 8/4 = 12+6+4+2 = 24

[General Lee]

Originally Posted by Dustin

Another approach to reduce the effectiveness of the extra layers could be to give the best layer its full DR, second gets half, third gets one-third, etc. So for the example of DR 8, 12, 12, and 12, it would add up to:

12 + 12/2 + 12/3 + 8/4 = 12+6+4+2 = 24

Yeah, I thought that something like that would be more scalable than the approach of the DR/3, or Armor as Dice for the matter, but still the 5d damage would not punch throught it.

Because of that, I think that both rules above explained better the article that makes me post this thread firstplace.

[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.