No, this is not about the weight of arrows.
Right now there is very little diversity of arrows and bolts, so, how about a new type of arrow just called heavy arrows? The normal 4 arrows could be be turned into heavy arrows, heavy barbed arrows, heavy Tatar arrows and heavy bodkin arrows. The only differences is that they will lower missile speed greatly and inhance damage slightly(if needed I can give you a physics lay down).
Thoughts?