Currently working on exotic sword. I've heard rocketyard is a good location, but haven't had much success.
Edit: Finished! I got bolt caster!
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Heads up. It sucks ass. When you spawn in, stay in that area and the moth yards. (The place with airplanes) Get a ghost with spin metal detector on it and a sniper. When you look through the sniper scope it will show you the spin metal anywhere on the map regardless of distance. Really expedites the process. Also you can only get it from the spin metal leaves, not chests. Probably knew that though. Second also, the map will only load so many items. As you start collecting spin metal leaves they will be replaced by chests or more leaves. So if it only loads ten items, and there are ten chests, you won't find spin metal until you pick up a chest. Good luck! Bolt caster kicks major ass!