Here are a couple of ideas I have for Artificer technology in Dungeon Fantasy, although it's obviously applicable to any GURPS fantasy campaign where Quick Gadgeteering is a legal trait. I'm trying to explore what's possible with TL 3 tech, not necessarily what's easy, so I haven't assigned Concept penalties or anything.
Energy storage at TL 3 exists in the form of mechanical tension and gravitational potential energy. Repeating crossbows are TL 2 and do thr+1 damage. Slings do sw or sw+1 damage, but of course they're much harder to use and not as accurate because you impart energy at the same time you're firing, whereas with crossbows you cock, aim, and then pull the trigger when you're ready. There's no fundamental reason you couldn't have a crossbow that does sw damage--you'd have to work out a way to cock it by banging it hard on something, and you still have to load the quarrel, but both of those are solveable problems. The best available regular crossbow (composite crossbow from MA) does thr+5 damage and takes four Readies to reload. Thus, it's not impossible that you could get a sw+5 imp crossbow that takes one Ready maneuver to reload, all at TL 3. (The repeating crossbow requires that you take your Ready to work the lever immediately before firing, but a Gadgeteer should be able to solve that problem.) It would be madly expensive and quite difficult to make, but hey, "a man's reach should exceed his grasp, or what's a heaven for?" Right?
GURPS: Martial Arts p. 232 also suggests barbed arrows that inflict half their damage again when pulled out. Why not spring-loaded expanding barbed arrowheads that inflict 1-2 points of damage on a succesful hit as a follow-up attack (i.e. ignores DR if the main attack penetrated) and increases pull-out damage by a like amount? They'll be heavy and not cost-effective, but sometimes more damage is, well, more damage. And sometimes mad inventors just like to play with their toys.
Armor is basically about putting big slabs of material between yourself and an attack. Fundamentally, armor is TL 0 (sandbags are DR 3 per inch and I believe sacks are TL 0), but the trick is getting personal armor that's light enough and flexible enough to still leave you mobile while protecting all your important bits. (If you ignore mobility requirements, burying yourself six feet deep in dirt with a snorkel up to the surface offers dandy protection, at least DR 36 to your whole body by my reckoning--interpolating from B559, I figure that dirt will protect less than sand but at least as much as the softest wood, which is 0.5 DR/inch.)
Therefore, you're really going to be limited chiefly by materials technology and by your ability to form joints with that material. DR in GURPS scales linearly with material thickness. A human male has a surface area of about three thousand square inches. Rolled steel weighs 0.2865 pounds per cubic inch, aluminum weighs 0.0955 pounds per cubic inch, and titanium is 0.1628 pounds per cubic inch. This implies that you could give a human male DR 10 over his whole body for about 120 pounds of weight using steel (maximum of 70 DR per inch of thickness) or 95 pounds of aluminum (maximum of 30 DR per inch), or 81 pounds of titanium (my sources indicate that titanium is about twice as "strong" as aluminum by volume and comparable to steel, although "strong" is a complex concept when it comes to armor, so I'm willing to defer to those with greater knowledge). Anyway, this sets an upper bound on the effectiveness/weight ratio of any low-tech armor, and no amount of clever inventions is going to exceed those bounds. However, Gadgeteering may be essential to actually letting you approach those bounds without losing mobility. One suggestion: GURPS allows you to layer two types of armor at the cost of a DX -1 penalty. A Quick Gadgeteer can invent a suit of armor which combines the weight, cost, and DR of both types of armor with no DX penalty. He can find a way to make the joints still more freely: as much a matter of ergonomics as metallurgy.
A pixie, on the other hand, has a surface area of about 21 square inches. You could theoretically layer him in 1 inch thick steel armor (increasing his surface area to 28 square inches in the process) with 10 pounds of steel. A hefty weight for a small creature, but pixies are strong for their size, and we're talking DR 70 here. On the other hand, it would take a ferociously gifted Gadgeteer to actually invent and build such armor.
So what about a suit of DR 10 plate armor with built-in repeating crossbows on both arms, firing spring-loaded barbed quarrels? Clench your fists to fire two quarrels, then slap your hands (hard) on your thighs to re-cock the crossbows and drop in fresh quarrels. (With the right Fast-draw/Heroic Archer abilities maybe you could even do it as a free action.) When the enemy gets close or you run out of ammo, just draw your greatsword and go to work, like a TL 3 Hatchetman (unfortunately without any Triple-Strength Myomer).
So, that's what I've got so far for TL 3: spring energy and personal armor. Open to more bright ideas.
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