I know giant bows aren't a novel concept on this site, but since I am trying to figure out a good ranged option for high-level Rangers, and I have a very specific concept, I will venture.
The bow itself is made of steel, along with the bowstring. As for size, it's made to fire javelin-sized flechettes (steel arrows) and is sized accordingly. Basically a giant steel longbow. Why steel? Because most monsters with acid attacks (or acidic/caustic physiology) do nothing or next to nothing against steel. Either way, that sums up a Greatbow.
My question is, How Useful Will A Greatbow Be?
Thanks to the Engineering class' discovery of advanced metalworking, steel of modern-grade quality can be created for this bow, which is meant to fire javelin-size flechettes as far and as hard as possible given the materials.
High-level Rangers (300 and up) can use (AKA nock, draw, and fire) this giant bow and its arrows with the same ease as a trained longbowman and have speed and range to match. EDIT: A Greatbow can fire its projectiles just as easily as it would fire an arrow of the right size for it, so expect supernaturally high range and force.
The bow is meant primarily for large, powerful monsters, with or without armor, such as a Giganto or the aforementioned Savage.
Specifications For Best Answer:
The best answer will first take into account how strong a Ranger would have to be to use a Greatbow.
Second, the best answer will determine and take into account the range and power of a Greatbow made of modern-grade steel.
Third, the best answer will determine how deadly (or destructive) a Greatbow's bolts would be.