Blowthrough and Armor as Dice

Apologies for references without links, but I’m behind a work firewall and for some reason they don’t want me surfing the SJG Forums from work. Unreasonable folks, corporate IT. It’s like they want me working or something.

In any case, there’s a weekly thread that got started up over on the GURPS forums called “Tweak of the Week.” It’s a neat brainstorming idea, and the first one on strength can be mined for good stuff.

I was pleased to find that the second one is about Armor as Dice, a concept I embrace (and while I may have published the first Pyramid Article on the topic, it seems to be a case of parallel evolution, since I remember way back when more than one person positing this as a solution to some perceived issues.

On that same thread, +Mark Langsdorf brings up a few cognitive challenges for Armor as Dice, which I can’t help with, and one issue of figuring blow-through, which I can.

So, since you roll damage and stuff after primary armor penetration, would you then have to convert left-over damage back to dice, etc., to figure out how to kill five giants, all in a row?

Dice, Dice Baby


I think the notional solution to this problem is to invoke the dice concept one more time.

Blow-through thresholds should be expressed in dice, based on the HP of the target. Ideally, a 10HP average guy would have about a 2d+1 blowthrough threshold, allowing a .45ACP to not typically overpenetrate, but a 9mm at 2d+2 will. But frankly, that’s more trouble than it’s worth. I’ll get to it later, though, for those that care.

Ultimately, just convert mass-based HP (or just use racial average HP) to dice, and for people, that would look like the chart to the right. For a 5-ton mecha, it’d be about 6dx2. 

So just look at the armor. If you’ve got (say) 6dx3 DR (DR 60-65 or so) on top of a 6dx2 mech by mass, and you hit it with a 6dx6(2) projectile (say, an APFSDSDU shell), you can look at a total interference of 6dx5 (DR plus HP), halved for the (2) AD to 6dx2.5. The downrange threat is thus 6dx6 – 6dx2.5, or 6dx3.5(2). That will penetrate the armor and the HP of the guy behind it, leaving a 6dx0.5(2), or 3d(2) threat, which won’t penetrate the third guy’s armor, but might be a threat to human personnel.

Parting Shot


It’s all about the dice, ’bout the dice.


Kidding aside, Armor as Dice is supposed to make things simpler, not more complex. You deal with dice as long as possible, and only convert to injury at the end.

The assumption inherent is that the injury is variable (and thus rolled), but the penetration is consistent enough – even through flesh and whatnot – to just treat as dice.

It should be simple, playable, and fast – though the issues such as keeping the mystery of what the foe’s stats are still remain, it’s designed to keep the math a bit more simple where it can be kept simple.

4 thoughts on “Blowthrough and Armor as Dice

  1. As I indicated in the thread, I eventually realized that I could just convert HP-for-overpenetration into armor dice and redo the dice subtraction for each target. My points were
    1) that it's not an obvious solution at the table
    2) dividing by 3.5 in the middle of an already hectic combat while you're looking up a rule for first time in ages is kind of pain.

    But this is an admittedly obscure corner case and I really prefer working with armor as dice in general. It's much easier to look at WWII tanks and tell if they can penetrate each other's armor if you're comparing 40d of armor to weapons that do 6dx7 damage than it is when comparing 140 DR of armor to 6dx7 damage, even though it's the exact same thing. 42d barely penetrates 40d of armor; that's obvious. 6dx7 maybe penetrates 140 DR, because 6d is ~20 and 20×7 is 140, but that's some annoying math.

    1. Unsurprisingly, precalculation is your friend here. If damage is in dice, and you convert mass-based HP into dice (and I say mass-based because there's a bit too much variability in blowthrough values), and DR into dice. That way, it's all pre-figured, and you don't ever do it at the table. List DR140 as DR 140 (6dx6.5) or something like that, but always have it handy.

  2. I've been leery of armor as dice because it seems like it would produce rather odd results.

    42d gun vs. 40d armor seems to lead to 2d penetration. Against a tank with 100-150 HP, this would seem to result in odd, ahistorical results of tanks slowly chipping in with 2d penetrations.

    In the "standard" version the much larger spread results in a good chance of bounce off or a fairly deep penetration (30-40 points), which if combined with, say, a hit to the vitals may lead to a kill.

    This seems far more realistic to me, given both a historical 15% or so deviation in penetration and the fact that actual armor variations across the frontal aspect of an AFV are likely to be much higher than GURPS models with its uniform frontal DR.

  3. My quick solution through the years with blow through has been to multiple HP with Pi damage of the gun. So .45 vs ST 10 man would have BT of 15 while 9×19 would have 10 and .22LR would have 5. Of Course hit locations like vitals would x3 blow through and brain x4.

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