Equipping the Dorgeshuun c'bow incorrectly requires completion of the 'The Lost Tribe' quest.
What I did: I attempted to equip a Dorgeshuun c'bow without having had done the 'The Lost Tribe' quest.
What I expected to happen: I expected to be able to equip the Dorgeshuun c'bow.
What actually happened: I was unable to equip the Dorgeshuun c'bow.
IDs of related NPCs/items: 8880
2009-era source (if relevant): https://runescape.wiki/w/Dorgeshuun_crossbow?direction=next&oldid=748780 - Source states that purchase from Nardok and use of the special attack, Snipe, are locked behind the quest, but it makes no mention that use of the crossbow itself is locked behind it.
Screenshots or video: I did not take a screenshot as I did not realise this was a bug until I looked up the crossbow for info on the special attack.