Piercing damage against low tech armor

[Rupert]

Originally Posted by Verjigorm

ST 13 is 1d+1 thrust, right?

1d thrust. Thus 1d+3 imp from a composite bow (reflex bow in LT).

.38 Specials gets 2d or 2d-1 pi in HT, depending on the pistol it's fired from .380 ACP gets 2d-1 pi.

So, yeah, I believe that the damage values of guns and bows are not anywhere near right. Medieval plate armor is not going to protect you against even notoriously under powered pistol calibers.

Which means rebuilding all the DR and damage/penetration values. Which is fine, but you'll end up with quite a different balance from that which GURPS currently has.

[Ulzgoroth]

Originally Posted by Verjigorm

So, yeah, I believe that the damage values of guns and bows are not anywhere near right. Medieval plate armor is not going to protect you against even notoriously under powered pistol calibers.

This is sort of tangential to the subject, but early modern plate armor almost certainly should protect against that. It did, after all, protect against balls from arquebus and the like. Which are a little more potent than those notoriously under powered pistol calibers.

[Icelander]

Originally Posted by Ulzgoroth

This is sort of tangential to the subject, but early modern plate armor almost certainly should protect against that. It did, after all, protect against balls from arquebus and the like. Which are a little more potent than those notoriously under powered pistol calibers.

Lead round balls penetrate a lot worse for their energy than small caliber modern rounds.

.22 LR doesn't have a lot of energy, comparatively speaking, but penetrates surprisingly well, especially the highest velocity loadings.

[Varyon]

Originally Posted by Icelander

Lead round balls penetrate a lot worse for their energy than small caliber modern rounds.

I've wondered before if pure-lead projectiles should have a (0.5) Armor Divisor, at least against hard armor. After all, I believe GURPS treats Jacketed Soft Point (which has exposed lead at the tip) the same as Hollow Point, giving both AD (0.5) (as well as +1 to pi-class, but a cylinder sees a lot more cross-sectional expansion upon smooshing than a sphere would, so I'm fine with not boosting the WM of lead ball).

I then realized that, if the weapons from LT had their damage based on their actual penetration (like many GURPS firearms), to keep them accurate you'd need to double their basic damage. So I promptly abandoned that line of thought, in favor of LT firearms not red-misting unarmored/lightly-armored PC's (the arquebus, at 2d+2 pi+, is already pretty roughly on such characters, averaging 13.5 HP per shot on an unarmored foe (~-1.5 HP per point of DR); change that to 4d+4 (0.5) pi+, you're looking at an average of 25.5 HP per shot on an unarmored foe (24 HP vs DR 1, ~-3 HP per additional point of DR). If the LT weapons based their penetration on some sort of hidden equation, however, and they failed to account for the softness of lead, it could be an option to keep damage as-is and give AD (0.5). Do note that doing so means plate armor of DR 10 or higher is "proof" against anything smaller than a cannon (and it's even proof against the smaller ones of those).

[Icelander]

The Low-Tech weapons used Vehicles 3e formulas and might be less realistic than I might like in many cases, but High-Tech has realistic weapons which fire essentially the same projectiles and the damage there is comparable.

So, lead ball damages are realistic. They won't expand as much as JSP, because the velocities involved are not sufficient to cause the massive expansion you see in modern hunting rounds.

The 'problem', as such, is that .22 LR and 5.56x45mm NATO/.223 Remington penetrate surprisingly well against some materials. Fractional armour divisors on a situational basis would be realistic, but too complex in play for GURPS to use it.

[Rupert]

Originally Posted by Icelander

Lead round balls penetrate a lot worse for their energy than small caliber modern rounds.

.22 LR doesn't have a lot of energy, comparatively speaking, but penetrates surprisingly well, especially the highest velocity loadings.

And yet most of those bullets are lead. Even those with copper tend to have a thin coating, not a jacket like larger bullets. What's more, they're only slightly better shaped than a lead ball.

.22LR isn't a very powerful round, but it's quite efficient.

[Ulzgoroth]

Notice that the .380 rounds that Verjigorm referenced are hardly small-caliber by TL6+ standards at 9mm, though they are a good bit smaller than TL4 or many TL5 loadings.

[Anthony]

Took a bit of poking around because most people aren't super concerned with the armor penetration behavior of .22LR, but I found a post where someone was comparing .22LR to .223 by shooting a few targets, including 16 gauge pipe (1.6mm, and pipe isn't exactly armor grade steel), and, well, .22LR failed to even penetrate one side of the pipe. Given that, it's quite plausible that low tech plate would stop .22LR, at least in a fairly vanilla loading (you can get exotic loads that are nominally .22LR).

Found a Youtube video as well, shooting 24 gauge sheet metal. It went through three layers, which is... not very impressive, but the shape of the recovered bullet is a good demonstration of why hard matters for bullets.

[Verjigorm]

Originally Posted by Ulzgoroth

Notice that the .380 rounds that Verjigorm referenced are hardly small-caliber by TL6+ standards at 9mm, though they are a good bit smaller than TL4 or many TL5 loadings.

While the .38 and .380 are sort of close in size to 9mm, that's about where the comparison stops. The FBI determined that .38 Special +P loads were not sufficient for law enforcement needs in the after-action analysis of the 1986 Miami-Dade Shoot-out, and led to them setting forth what are essentially the most widely accepted criteria for the effectiveness of a pistol cartridge for law enforcement purposes. The FBI specifies that a minimum of 12" of penetration is required, but penetration in excess of 18" is penalized. This is, in the opinion of the FBI, the minimum amount of tissue you need to penetrate to be able to reliably reach vital organs and cause immediate or sudden incapacitation.

.38 +P+ is a round that's comparable to 9mm, but... well, then we're talking about "combat pistol" rounds, as compared to pistols that are primarily intended to easily concealable.

[Rupert]

When shooting 1/4" inch mild steel plate, at about 15 yards, 5.56x56mm rounds (old-style, pre-SS109 bullets, so not great penetrators) went through it about 90% of the time. 7.62x39mm ball (soft steel core) went through without any trouble at all. So did .243 Winchester hunting (soft-point) rounds, and every modern rifle more powerful than that.

12 gauge shotgun slugs made dents about 1/2" deep in the plate, but it showed no signs of giving way. A replica US civil war rifle firing Minié bullets made a smaller dent of about the same depth. A modern muzzle-loaded .45 black powder rifle loaded very high made some deep pits but didn't penetrate, and that's about the best I'd expect of soft lead balls - you could see that they were 'splashing' on impact.

.22LR of various powers including several brands of extra-powerful loads just made little pock marks and dimples.

So .22 LR and pistol calibres can be expected to be stopped by 1/4" mild steel plate (DR 14 at most - the plate was far from new even before we put a whole lot of bullets into it), for what that's worth.

Unfortunately my father wouldn't let us try out the piece of armour plate off a universal carrier, so I can't say how much difference that makes from personal empirical testing.

However, .22 LR bullets penetrate wood far better than you'd expect from this. I assume their relatively low velocity allows them to push fibres aside somewhat, when high velocity bullets just smash their way through, losing energy faster.