I don't think there has ever been a Legendary shoot to loot weapon before. If there has been, it's probably pretty rare. This will be the first weapon I buy when HoW is released! You can see the sniper, and it's perks in DPJ's video: http://youtu.be/1EPMZkv8RCA
The sniper is around the 3:46 mark.
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Nightfall is about the only time I use it. It would be nice to have a Legendary one however.