A Mithril Crossbow (level 36 ranging) or better.
Monster Drop (Chaos druids), Player made with the Smithing skill. Smithing level 53 required and gives 50 exp. Requires one Mithril bar (to make the bolttips). Then use your fletching skill to attach feathers (level 54 Fletching needed and gives 5 exp per bolt). Also dropped by red dragons.
Used as ammo for Mithril crossbows and better.
Used in the ranging skill, you must use a Mithril crossbow or better to fire these bolts, a Mitril crossbow requires at least level 36 ranging to use it.
Can also be player made.
Mithril crossbow bolts.