It takes more than that to kill a Bull Moose.
The Rare Shield The Rough Rider is manufactured by Jakobs and comes from the Borderlands 2 Big Game Hunt - DLC.
This Shield has technically 100 Capacity, but never recharges.
The 0 Capacity will activate skills that are linked to shield depletion.
The Rough Rider's Drop-Rates and all Sources:
3 Epics count as legendary ingredients and may come as a result: Deadly Bloom, Supernova, Cryo Spike