H&K MP7A1 versus Ballistic Helmet [High-Tech]

[Ragitsu]

Originally Posted by Anthony

First of all, GURPS has issues with armor layering.

Asides from this specific failing in the rules, what other issues do you speak of? I'm interested to hear them.

[Anthony]

Originally Posted by Ragitsu

Asides from this specific failing in the rules, what other issues do you speak of?

In the real world, two layers of armor do not provide the same protection as one layer of double thickness armor. The exact details depend on the nature of the attack and the spacing of the layers, but typically the double thickness layer provides well over twice the protection.

[DouglasCole]

Originally Posted by Ragitsu

Average damage (3s on all d of a 5d caliber) is 15 for the 5.56mm, right?

As for the pistol: http://www.gunblast.com/Bushmaster-Pistol.htm

Usually one uses 3.5 per die to figure average damage. This is explicitly how firearm damages are calibrated, by the way: 20d = DR70 = penetrates "one inch of Rolled Homogenous Armor steel"

RHA isn't the greatest steel armor in the world, but it is a standard. That's one of both the benefits and quirks of GURPS, and why firearms and fists or even bows are so wonky at some levels; the Penetration of homogenous armor is DARN good representation, by and large. How that translates as through-armor (or even no-armor) injury requires rather a lot of tap dancing, witness arguments about bleeding, blow through, the variability of wounding, etc.

[SimonAce]

I never had much of a problem with the 4.7 round in GURPS. I suspect it might have a bit too much penetration (average of what 26 or something) but given the standard round is 30 grains AP at about 2400 FPS using Tl8 design (as vs the TL7 M16 round) I can buy it

Besides it only does 1/4 damage to a human (std round is AP) -- thats about 1d6 or so against flesh

Say you roll very well and get 20 points -- thats 1/2 vs armor -- say 12 points -- drops you to 8 divide by 4 (ap and size) and your target takes a big honking 2 points

[Ragitsu]

A burst of 4.6mm to the vitals, even at a target wearing a basic ballistic vest, is going to seriously wound or kill them.

[tshiggins]

Originally Posted by nick012000

Yes. Helmet has 12 DR, and the gun does an average of 15 damage before damage multipliers are taken into account.

Moreover, helmets are primarily designed to stop the things mostly likely to cause injuries to the head -- shrapnel, as well as the rocks and splinters that get kicked up when an explosive charge goes off nearby. They're not made to stop bullets. The odds of injury from getting shot anywhere (much less the head) are much smaller than the chance of injury from explosives (artillery, mortars, IEDs, etc.).

A quarter-pound rock thrown up by a mortar that nails you in the chest is gonna hurt, but you'll mostly swear a lot, may holler for a medic, but will probably walk it off. That same rock to the noggin, on the other hand, could put you down and out for a long time.

[Ragitsu]

I take it you didn't buy into the marketing strategy either ;-)?

[Fred Brackin]

Originally Posted by Ragitsu

I take it you didn't buy into the marketing strategy either ;-)?

Within it's limited niche the HK is probably a better weapon than the P90 but the "PDW" concept is almost certainly a failure.

You're just not going to issue one of these to everyone who isn't carrying a bigger weapon. It's a specialist's weapon rather than a general purpose one.

You give it to Spec Ops who need an ultra-compact weapon with good AP qualities and can still manage to put multiple shots into the vitals. You don't give it to low skill users so they can spray and pray.

[DouglasCole]

Originally Posted by SimonAce

I never had much of a problem with the 4.7 round in GURPS. I suspect it might have a bit too much penetration (average of what 26 or something) but given the standard round is 30 grains AP at about 2400 FPS using Tl8 design (as vs the TL7 M16 round) I can buy it

Besides it only does 1/4 damage to a human (std round is AP) -- thats about 1d6 or so against flesh

Say you roll very well and get 20 points -- thats 1/2 vs armor -- say 12 points -- drops you to 8 divide by 4 (ap and size) and your target takes a big honking 2 points

Here's the basic argument in a nutshell:

M16 round (M193 5.56x45mm, 55gr / 993m/s ) is 1760J, 55gr and 5.6mm.
5.7x28mm SS190 round: 31gr at 715m/s. 514J, 31gr and 5.7mm
4.6x33mm round: 25gr at 725m/s. 420J, 25 gr, and 4.6mm.

Penetration in GURPS (and more or less in real life) goes basically as sqrt(KE), and inversely with the cross section of the bullet, but a much weaker function.

Still, let's look at the first two: the M16 round is 3.42x the energy and basically equal cross section, so the basic damage should be sqrt(3.42) = 1.85 times less. Versus the 5d universally accepted (and well proven through empirical studies) that the M193 round gets out of our M16, the P90 round should be 2.7 dice of damage. That's 2d+2.45, call it 2d+2.

Now, if you've seen the SS190 round, it's POINTY. It's also constructed as an armor piercer, which perhaps makes it eke out something between a 1.5 and 2 armor divisor. Possibly. But I'd expect that of the two bullets, the M16 would be superior. Possibly VERY superior. But it ain't.

[Kale]

Originally Posted by Fred Brackin

You give it to Spec Ops who need an ultra-compact weapon with good AP qualities and can still manage to put multiple shots into the vitals. You don't give it to low skill users so they can spray and pray.

I've seen PDWs issued to SWAT teams up here in Canada. I saw a newspaper article about a SWAT action in Montreal and in the photo all the cops had P90s.
I can't see it being issued to mainline troops or the like, although I thought I remember that Saudi Arabia bought a big pile of them for its military. (Then again they are filthy rich and can probably afford it.)