The RAW does a great job of defining the categories for melee weapons in terms of how they are used and their encumbrance factors in combat (light, one-handed, two-handed) and they then extend this set of definitions into "size categories" that help to give an idea of the actual size of the object. Thus, a light weapon (such as a dagger) for a medium character is two sizes categories smaller than the character, and so a dagger is roughly a tiny sized object.
All this works well at giving a rough estimation of how big various weapons are in the game.
However ranged projectile weapons don't fall into the handedness categories, and so you can't easily extrapolate the size of the object.
Is there any commentary or analysis that helps flesh this out a bit, either from Pathfinder or 3.x sources?
