This is an (almost?) complete set of the best projectile weapons in LOTRO as of Book 13, drawn from my priceless collection. Cudur, Bane of Forvengwath and Fortified Black Ash Bow are clearly the best available. I normally have Cudur equipped, and carry the other two in my pack. Cudur becomes available after you reach Rank 4 with the Free Peoples in the Ettenmoors; it costs 3 Luminous Spirit Stones and a further quantity of Glimmering and Dull stones, all of which can either be found in the Delvings of Fror or purchased at the AH. It should be possible to achieve Rank 4 after 2-3 days fighting in the Ettens.
Bane of Forvengwath drops from the first Gatekeeper in Balad Gularan; unfortunately it seems to be fairly rare drop; on the plus side, he isn't that hard to down, and a determined fellowship could farm him. Fortified Black Ash Bow is of course a crafted item. Bow of Keria is a reward item for completing Book 13, and therefore quite achievable for a l.46 or so player. Bow of the Hunt is the reward item for completing the Hunter class quest; it's a nice bow, but usually, by the time most Hunters complete the quest, they will be close to getting something better.
The crossbow Nathfeig, another Barad Gularan drop, is useful to keep around when going after dragon kind (+7), which includes all the worms. Gautar's Ironwork Crossbow (an Angmar/Myrkworth drop) is the best I've been able to come up with as far as dealing out ancient dwarf-make damage is concerned, but there may be something better out there. Finally, Tongannel's Joy is a reward for the Trollshaws quest "Cause for Joy" which comes in very handy when you're in the mid-40s, and was my favourite bow for a long time.