They are rare. The higher your light is, the better chance you have. I've been grinding and was only able to get 297 without any raid pieces. Just found a 300 rare sniper that put my sniper to 300. I did raid on two characters up to oryx and got to 299. Beating oryx will get me past 300. My hold ups are helm, ghost and primary. I should get that tonight as I have 20 oryx shards. That gives you 3-4 loot drops from him.