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Old 05-16-2020, 10:19 PM   #1
Join Date: Mar 2013
Default [HT] Hypothetical Multi-Purpose Shotgun Slug

Hey all,

So, I don't post frequently enough for ya'll to have picked up on this, but I L-O-V-E love GURPS shotguns. Like, they are hands down my favorite kind of weapon, and a lot of my characters that probably shouldn't use them end up doing so because I just love them so gosh darn much. It all started with a velocity-boosted Gauss CAW with HEMP rounds and an extended magazine with an integral non-rechargeable power cell, and the rest was history.

Having watch quite a few Taofledermaus videos on Youtube, the idea of a custom round formed in my head. A solid lead or steel slug with a tungsten carbide penetrator for defeating armor. My question is how realistic is this sort of shell, could it work, and, most importantly, how would one stat it in GURPS. I whipped up the attached graphic in MSPaint in about 10 minutes to better illustrate the idea, which is (of course) not to any kind of exacting specificity.

The basic idea is that when the slug strikes, the WC rod strikes first and continues through targets too tough for the slug to penetrate. On softer targets, the slug strikes as it normally would, not sacrificing wound potential. The polycarbonate sleeve makes separation easier for the WC rod and equalizes the additional density of the denser material, giving the slug the same overall density and thus (hopefully) virtually identical aerodynamics and performance.

Here's hoping the fantastic Mr. Cole is trolling the forums,

Thanks everyone for listening to me gush, ya'll are still the absolute best,

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Old 05-17-2020, 07:00 AM   #2
Join Date: Jun 2013
Default Re: [HT] Hypothetical Multi-Purpose Shotgun Slug

I've considered something like this in the past, and for more than just shotgun slugs, although I dismissed it assuming it wouldn't be as useful as I was hoping. The design would probably resemble the Hydra Shok, but with the center post made of tungsten carbide (or other armor penetrating material) that is weakly attached to the base, rather than formed from the bullet material. You need something designed to mushroom out, as otherwise the lead will probably go inward as well, likely trapping the penetrator. In theory, on impact the penetrator would detach, going deeper than the rest of the (hollow-point) bullet. In practice, however, I suspect the penetrator would be too light to go very deep at all, invalidating the design.

Assuming you can make the penetrator around half the weight of the rest of the round, and for simplicity we'll say it goes the entire length, the penetrator would have roughly half the kinetic energy (which scales linearly with mass) and 65% of the caliber of the round itself. If a non-expanding round of the same same size, density, and velocity would penetrate, say, 10 inches, the penetrator (going off of Douglas Cole's spreadsheet) would have 80% of the penetration of the non-expanding round. The expanding portion, meanwhile, would have half the kinetic energy but normal caliber, for 70% of the penetration. So, unless I'm misinterpreting things, against an unarmored target the weapon would function as a hollow-point round with 70% of normal damage, while against an armored one it would have 80% of the normal damage (and -1 to wounding class) of a solid round. Technically, the performance against an unarmored target would be a bit better than the above, as the penetrator would still do its damage - you'd be looking at 70% at +1 wounding class, 10% (80% minus 70%) at -1 wounding class; for 5d pi+, that's an average of 24.5 HP + 1.75 HP, or 26.25 HP, equal to the wounding from a solid slug. Honestly, considering the penetrator has less penetration than a solid slug, this means the design is invalid - against an unarmored target, it does no more wounding than a solid slug, and against an armored target, it has inferior penetration (and wounding, as most of the wounding character is eaten up by the armor) to a solid slug, unless I'm missing something (and I may be, I'm not certain exactly how Cole's spreadsheet handles armor-penetrating materials).

That said, at least in a cinematic setting, feel free to have this design function better. Something like 80% damage, and use the higher wounding of if the round were HP (+1 wounding class, AD (2)) or APHC (-1 wounding class, AD (2)). To work for a 12G shotgun, you'd need to allow for a pi+++ class (wounding modifier 2.5 or 3, up to you; we'll go with 3). So, a solid 12G shotgun slug is 5d pi++, an HP 12G shotgun slug is 5d (0.5) pi+++, an APHC 12G shotgun slug is 5d (2) pi+, and our bullet (we'll call it APDP, Armor Piercing Detached Penetrator) is the better of 4d (0.5) pi+++ and 4d (2) pi+.

Using 3.5 per die (technically, when DR comes into play this understates the average wounding a bit, as it effectively counts negative wounding results, but it's close enough), against a target with DR 0, a solid slug deals 35 HP wounding, an HP slug deals 49.5 HP wounding (remember, poor armor divisors mean -1 damage against unarmored foes), an APHC slug does 26.25 HP wounding, and an APDP slug does the better of 39 HP wounding (hollow-point) and 21 HP wounding; obviously, 39 is better. Against a foe with DR 5, these become 25 for solid, 22.5 for HP, 22.5 for APHC, and the better of 12 and 17.25 for APDP (17.25). Against a foe with DR 10, this is instead 15 HP for solid, 0 HP for HP, 18.75 HP for APHC, and the better of 0 and 13.5 for APDP (13.5). Note this still isn't great, but if you're expecting to go up against foes who have a mix of DR levels, it could be worthwhile as an all-around projectile. x2 cost (comparable to APHC) would be fair, x3 may be more likely (it's a fiddly round to produce).

Of course, for a really cinematic setting, just treat it as the better of HP and APHC.
GURPS Overhaul
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Old 05-17-2020, 05:14 PM   #3
Join Date: Mar 2013
Default Re: [HT] Hypothetical Multi-Purpose Shotgun Slug

Originally Posted by Varyon View Post
I've considered something like this in the past....
My first thought was to label it as 4d pi++ with a linked 4d(2) pi- with 1/2D, Max, and Acc as a standard Rifled Slug, giving it the same overall wounding potential but making it much better against armor that would otherwise stop a slug cold, but I don't know how realistic that is. You'd still have to deal with the very real problem of over-penetration for the penetrator and if the initial slug blows all the way through a soft target on its own and renders the penetrator useless, it deals less overall damage than a regular slug.

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Old 05-18-2020, 04:29 AM   #4
Join Date: Aug 2004
Location: Udine, Italy
Default Re: [HT] Hypothetical Multi-Purpose Shotgun Slug

I might be wrong, but I suspect that these rounds do already exist in reality and are not even experimental any more. And yes, you can stat them in GURPS, with GURPS High Tech, p. 103. The box on that page provides examples of APHC slugs for shotguns. They get an armor divisor of (2). Also compare with p. 167.
Michele Armellini
GURPS Locations: St. George's Cathedral

Last edited by Michele; 05-18-2020 at 07:13 AM.
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armor divisor, high-tech, inventing, rifled slug, shotguns

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