Probably just an oversight, but the section of the bounty in which you must dismantle "10 rare or higher quality fusion rifles" does not seem to count Exotic as such a quality.
I had 9 rare fusion rifles and a spare Plan C, expecting to be able to complete the bounty, but I didn't get Fusion Rifle Energy out of the Plan C.
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I wouldn't bother going through with the bounty. It sucks compared to Plan C.