If you want an explanation, Jurassic Park was on a few days ago
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Anyway, the things were even bigger than elephants- about 20' tall, and six tons. So I think they'd need an even bigger bow and arrow than needed for elephant (100#, 1500 grain arrow).
So, how big? Since the heart/lung of the things were pretty high up (10-15 feet), the bow would have to be strong enough to toss the spear (the 5 ounce arrow) up there, all the wile you're at least 25-30 yards back (they do sem to like people-mc'nuggets!). So what, 150#? Or more?
The bow would need to be long, about 80" or so, with a long draw (30-32"), so the finished bow would be much like an Old War Bow, and since I like to make D bows, it pretty much would be.
So, for the fun of it, what do you all think would be necessary?
And yes, once I figure this out, I will start trying to make this stuff