Yeah, I know, a weapons thread. However, I think this one is different because it wouldn't involve adding completely new and massively powerful stuff (such as a railgun or battle laser) to the game, instead just building on what vanilla Minecraft already has (eg. pickaxe --> drill, axe --> chainsaw, furnace --> electric furnace, etc.).
I see a carbon fibre bow as behaving much like the normal bow, but with greatly increased durability, *less* damage (since carbon arrows are lighter and thinner than wooden arrows) and a much flatter trajectory (along with higher arrow speed?). Perhaps the carbon bow could also be drawn slightly faster to maximum charge than the vanilla bow (presumably, it would be easier to draw a bow made of modern materials for the same arrow energy)?
It would be created like so:
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where is either string or raw carbon fibres and is a carbon plate. .. indicates a gap (so it's crafted like the vanilla bow, but with different ingredients).
Alternatively, the centre piece could be advanced alloy, indicated by :
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Likewise, carbon fibre arrows would be a nice counterpart to the carbon fibre bow, which have a tendency to destroy wooden arrows in reality should you attempt to shoot a wooden arrow from a carbon bow. They'd be crafted just like normal arrows, but with refined iron or bronze instead of flint, a carbon plate instead of the stick and perhaps another carbon plate instead of the feathers - like this (again, is a carbon plate):
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8 arrows (maybe even 12?) from one of these recipes sounds like a reasonable output, since the metal tip on a carbon fibre arrow is very small and the arrows themselves are usually hollow (so they won't use a lot of carbon plate material).