They aren't bugged. They are simulated somewhat crudely:
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Weapons consist of only one material, so the calculations assume solid metal spears and whips.
Weapons are assumed to be rigid, for whips, this means we have ~1kg of metal impacting at supersonic speeds instead of a bullet-like tip.
Weapons aren't simply turned away, they hit perfectly straight and either penetrate or not. Needles would poke through armour like butter.
Weapons of the same weight all handle the same. A weapon balanced towards the tip may benefit from a higher velocity multiplier, but it won't be harder to handle (chance to parry, recovery speed).
Weapons don't receive damage.
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And adamantine is indeed quite nonsensical, which I ranted about often enough.
It has the density of balsa wood when solid, the density of normal stone when liquid. Solidifying adamantine would gain 12 times its current volume.
If I understand the properties right, a max_edge exceeding obsidian shouldn't be possible with its molar mass and density (obsidan fractures to edges a couple of molecules wide).
Urist Da Vinci already pointed out the problems with its perfect rigidity.
I always felt it was an unsightly blemish on the otherwise very cool materials system, created by 'let's pull extreme values out of nowhere' rather than 'let's think what we expect our god metal to be like, then simulate that'.
To which the reaction by most players seems to be 'shut up, we don't want it to be just slightly better steel'... which in my opinion misses the point.
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Not getting into the details of weapon usefulness, as I've written far too much about that already. Perhaps I should sum it up some time and link to it/put it in my sig.