Realistic DR for rigid armor

[Gustavus Adolphus]

Maximum damage is a shot that hit a weak point in the armor, and for most TL 4 firearms is about as likely as a critical hit. When determining what armor is considered "proof" against, you should really use average damage, as this is what real-world tests typically check for.

I use another DR for weak points of armor, because I consider automatically maximum damage one point-blank shot vs. an immobile target (and in my HR, critic is only a hit with maximum damage, because I don't want see things like swords who cut plate armors with one lucky shot). In fact in my HR I've recalibrate the power of most guns with caliber major than 7.62x51mm because of this.

[Varyon]

Originally Posted by Gustavus Adolphus

I use another DR for weak points of armor, because I consider automatically maximum damage one point-blank shot vs. an immobile target (and in my HR, critic is only a hit with maximum damage, because I don't want see things like swords who cut plate armors with one lucky shot). In fact in my HR I've recalibrate the power of most guns with caliber major than 7.62x51mm because of this.

Fair enough, but still note that firearms in GURPS are scaled with the assumption that 1 inch of RHA steel is DR 70 and will stop 20d. Thus, you'll need to figure out how much RHA each weapon can penetrate (dividing damage by 20d will give you this value in inches - multiply by 25.4 to get it in mm), and note that RHA probably has a W of 1.5 in your house rule. So, that musket from Low Tech, which is normally 4d+2 (penetrating 5.8 mm of RHA) should instead be 9d+1 (I originally had this as 15d+2, but that's if using average rather than maximum damage).

[Polydamas]

Originally Posted by Gustavus Adolphus

@Polydamas: but this is also incoherent with stopping power and wounds. If one ST 10 ordinary man could do 60 to 130 Joule of force with a 1kg one-handed weapon (typical sw 1d+1; 2-7 damage, coherent because penetrating flesh requires a little extra amount of energy), one ST 12 man with a two-handed weapon could reach ca. 200 Joule of force (sw 1d+5, 6-11 damage). This is quite linear, not quadratic, I think.

PS: corrected 'cause my very bad English!

A ST 12 man is about 1.44 times as strong as a ST 10 man (he can lift 1.44 times the weight, etc.) so ought to deliver 1.44 times as much energy and 1.2 times as much damage. Unfortunately, the swung and thrust damage chart was invented for a game about gladiators before anyone had thought seriously about how to model ballistics and wounding in GURPS, so it is not very realistic or consistent with the rest of the system.

When authors create stats for firearms and armour, they use the model "damage is proportion to the square root of energy divided by projectile diameter, DR of a plate is proportional to thickness." Of course you can change that, but if you change what DR represents, you should change what damage represents too. The firearms and armour in low tech have damage and DR based on Alan Williams' book and the experiments at Gratz.

Many people want to change the GURPS rules to be more realistic about armour and weapons, but it is hard work. Good luck!

[Gustavus Adolphus]

Originally Posted by Varyon

Fair enough, but still note that firearms in GURPS are scaled with the assumption that 1 inch of RHA steel is DR 70

Well, in current linear DR increment rules, the TL3 iron is more resistant than RHA steel.

2,54 cm of RHA steel = DR 70
2 mm of TL3 iron (medium plate) = DR 6; 2,54 cm of TL3 iron = DR 76.2
A TL3 medium plate armor for a colossal fantasy titan is more resistant than tank RHA covering, according to GURPS rules.

I use the Petry's formula:
http://www.earmi.it/balistica/img/perry.gif

D is the penetration in cm, K is the materials coefficient, P is the bullet's weight in grams, C is the bullet's caliber in cm and V is the impact speed of the bullet.
In following days I'll publish some interesting results.

I forgot, in my HR I use GURPS 3 Accuracy for firearms (with eventual penality under the enemy's fire) and I use the following rule:
Damage Dices roll increased by 1 (maximum 6) if the hit has 5+ margin of success and increased by 2 if the hit has 10+ margin of success. Media of dice roll may become 4.33 or even 5 instead 3.5, so one proofed armor must allow to survive against a good shot without any risk of K.O.

-

@Polydamas: strangely, I find more accurate the melee damage, at least until ST 16, the human ST limit (extremely rare but possible, ex. the GoT character "The Mountain").

-ST 10: sw 1d (1-6, medium damage 3.5, Maximum Damage 6)
-ST 11 (BL x1.21): sw 1d+1 (2-7, m.d. 4.5, MD 7); md 4.5/3.5 = x1.28, MD 7/6=x1.16
-ST 12 (BL x1.44): sw 1d+2 (3-8, md 5.5, MD 8); md 5.5/3.5 = x1.57, MD 8/6=x1.33
-ST 13 (BL x1.69): sw 2d-1 (2-11 [minimum 1 BD per dice], md 6.58, MD 11); md 6.58/3.5 = x1.88, MD 11/6=x1.83
-ST 14 (BL x1.96): sw 2d (2-12, md 7, MD 12); md 7/3.5 = x2, MD 12/6 = x2
-ST 15 (BL x2.25): sw 2d+1 (3-13, md 8, MD 13); md 8/3.5 = x2.28, MD 13/6 = x2.16
-ST 16 (BL x2.56): sw 2d+2 (4-14, md 9, MD 14); md 9/3.5 = x2.57, MD 14/6 = x2.33

Well, STRENGHT is quadratic, but according with these results, Basic Damage and DR by themselves are linear, so DR 2 isn't four times more resistant than DR 1 and 5 BD isn't 25 times the impact force of BD 1.

[Tomsdad]

Originally Posted by Gustavus Adolphus

...
WITH GURPS LOW-TECH RULES:
Gonne: 2d pi++ (medium 7 BD, maximum 12 BD)
vs. Gothic armor (iron medium plate armor with DR 6 plus 1 DR padding): 0-5 BD = 0-10 total damage (15 if the shot hits the vitals)
vs. Milanese armor (steel medium plate armor with DR 7 plus 1 DR padding): 0-4 BD = 0-8 total damage (12 if the shot hits the vitals)
...

I think you might like Load Outs Armour low tech, its written by Dan Howard (a man who I know has read tKatBF).

A C16th Milanese plate is DR9 on the breast plate that will stop a lot of damage, the English Cival war 'proofed' breastplate is DR12 (but of course heavy as ****) and there's no real reason why your ritter or conditorrie couldn't have one, its just they were facing proportionally less gun fire then your civil war Lobster.

That's also without the various mods available for hardening, duplex, tailoring etc.

Another thing that comes up a lot in the load outs is layering, it happened, and it happened quite a lot. (Noticeable at lower TLs plate and mail is layered to give the same DR that plate alone can reach at high TL4, although the abdomen is still layered).

If you really want to have the ridiculously thick stuff then there's an article in pyramid lowtech 2 that has various materials DR by weight, cost and thickness. (I find this works for high ST characters vs. high ST characters who can wear un-historically thick, heavy stuff).


One last thing to say about The Knight and the Blast Furnace I recognise the figures you using are from the final chapter outlining the experiments and assumptions. But do remember that definition of penetrating blows was a blow that would stop an opponent. I.e a point or two of damage (especially damage that has been turned into crushing by edge protection) is probably still within tKatBF's definition of a stopped blow.

TKatBF was not written with modelling incremental damage for RPGs in mind, but for showing how good armour would save your life and keep you fighting.

DR6 of plate will stop 9pts of cutting damge and 12 of Imp damge, that is in GURPS quite alot.

[Gustavus Adolphus]

Originally Posted by Tomsdad

I think you might like Load Outs Armour low tech, its written by Dan Howard (a man who I know has read tKatBF).

A C16th Milanese plate is DR9 on the breast plate that will stop a lot of damage, the English Cival war 'proofed' breastplate is DR12 (but of course heavy as ****)

Well, according to my HR, the typical rounded heavy cuirassier breastplate (the thickest part of armor, 4mm, but made in very bad iron, W = 0.5) has exactly DR 12
Formula: DR = 6 x (4mm/2mm)^1.6 x (0.5/0.75) = 12 (12.12 rounded down), DR 13 with padding or a light buff coat.

Muskets (4d+2 pi++) can reach more than 3000 J (but they have heavy round caliber and lead balls are 20% less effective than equal caliber and form jacketed slugs), and heavy non-portable muskets can reach even 7000 J (the monstrous 9d+1 pi++ cited by Varyon)

[Varyon]

Originally Posted by Gustavus Adolphus

2 mm of TL3 iron (medium plate) = DR 6

Whoa, whoa, hold up. Where are you getting these data from? Using Low Tech Armor Design (Pyramid #3/52), a 20 lb plate cuirass made of good iron (DR/inch of 68) is around 2.25 mm thick and provides DR 6.

Originally Posted by Gustavus Adolphus

Well, STRENGHT is quadratic, but according with these results, Basic Damage and DR by themselves are linear, so DR 2 isn't four times more resistant than DR 1 and 5 BD isn't 25 times the impact force of BD 1.

Again, the ST based damage chart isn't very realistic, and every other damage calculation used in GURPS is quadratic, from firearms to explosions to beam weapons. I'm afraid I can't realistically accept someone slinging a bullet and getting more penetration out of it than a typical TL4 pistol (ST 16 matches the petronel, which again is more like a carbine than a pistol).

[Gustavus Adolphus]

Originally Posted by Varyon

Whoa, whoa, hold up. Where are you getting these data from? Using Low Tech Armor Design (Pyramid #3/52), a 20 lb plate cuirass made of good iron (DR/inch of 68) is around 2.25 mm thick and provides DR 6.

Actually, if you use Mosteller formula to calculate body surface area, a DR 6 20 lb breastplate made of iron for a standard-sized man (1.72 m x 70 kg) is exactly 2 mm thick. Iron, not steel, steel armor has an extra +1 DR.

So, iron is stronger than RHA steel?

[Tomsdad]

Originally Posted by Gustavus Adolphus

Well, according to my HR, the typical rounded heavy cuirassier breastplate (the thickest part of armor, 4mm, but made in very bad iron, W = 0.5) has exactly DR 12

Well there you go then (honestly Load out lowtech armour is well worth the money) 4mm is very thick but yours is based on very bad iron, The the load out isn't.

Originally Posted by Gustavus Adolphus

Formula: DR = 6 x (4mm/2mm)^1.6 x (0.5/0.75) = 12 (12.12 rounded down), DR 13 with padding or a light buff coat.

I see your using the Power1.6 from tKatBF which as people have said is counter to how armour works in GURPS but so long as you get similar result I guess it doesn't matter too much.

Remember that formula is to match the overall effect of everything in combination up to and including a serious wound .

Originally Posted by Gustavus Adolphus

Muskets (4d+2 pi++) can reach more than 3000 J (but they have heavy round caliber and lead balls are 20% less effective than equal caliber and form jacketed slugs),

Yeah but it was an arms race between proofed armour and firearms, Firearms were made better and heavier to beat armour, armour was made better and thicker to beat firearms etc. etc. Ultimately muskets won, but they were big and heavy.

The reality is a DR12-14 (depending on what else you do) will likely save your life when getting hit by a musket.

Also the half damage range is a bit generous and all or nothing in effect here. The penetration power of low velocity lead shot dropped off reasonably quickly. (although long range shots were rare anyway).

What I think happens here is people look the fire arms tables on Low tech and say "look, the musket still penetrates and can leave nasty wounds, armour is broken in GURPS". Well that's what muskets were there for, and at the time they were facing such armour they were 20lb specialised bits of kit wielded by elites.

But I think you have to look at that table in terms of what heavy DR12-14 renders you immune or largely resistant to, and its pretty much all of it. I.e it takes a 20lb musket with a rest to beat such armour.

Originally Posted by Gustavus Adolphus

and heavy non-portable muskets can reach even 7000 J (the monstrous 9d+1 pi++ cited by Varyon)

Sorry I don't think Varyon was making a new weapon, I think we just adjusting the current musket's ability to penetrate using materials other than RHA as the basic calculation. So I don't think it would be 9d+1 pi++ but just 9d+1 pi. So you'd get better penetration of that material but penetrating damage would be equal (4d+2)x2 pretty much equals 9d+1.

There is a wall gun thats 5d+ something , but that's a wall gun.

[Varyon]

Originally Posted by Gustavus Adolphus

Actually, if you use Mosteller formula to calculate body surface area, a DR 6 20 lb breastplate made of iron for a standard-sized man (1.72 m x 70 kg) is exactly 2 mm thick. Iron, not steel, steel armor has an extra +1 DR.

So, iron is stronger than RHA steel?

Steel armor (DR 70/inch) has about the same DR as good iron (DR 68/inch), it's Hardened Steel that gets the +1 DR (the Pyramid article has Hard Steel giving 16-20% more DR for the weight, but Dan Howard has noted previously that TL 4 metallurgy wasn't really up to the task of producing thick plates of such uniform hardness, and that a flat +1 DR was probably the most realistic compromise).

I realize now I misunderstood what the Construction Weight Modifier for Plate really represents - it's for the angling of the armor to reduce the chance of a blow "biting," as well as weight reductions in areas that aren't considered very vulnerable (Chinks in Armor and Armor Gaps). A 20 lb iron breastplate that was 2 mm thick would lack such modifications and thus wouldn't have weak points, but would be more-or-less impossible to construct for the human form. Such a theoretical breastplate would use the Solid (rather than Plate) construction, and would provide DR 4.76 (which we could be kind and round up to 5). As it stands, a 20 lb Plate breastplate is going to be mostly around 2.25 mm thick (it can probably get away with being a bit thinner, thanks to angling tricks), but with some thinner areas (Chinks in Armor) and outright gaps making up the difference.