I had a buddy that went after them rather aggressively .
He got permission to hunt on a ranch that had a decent size stock pond on it.
He'd wait until a herd of them came down to drink.
He'd start at the back, and work towards the ones in the water.
He'd get 5-7-8 of them with a standard AR in 5.56 with the max. load for 55 or 60 grain spire points.