I just picked up a Weatherby Vanguard .300 Winn Mag w/ 28" barrell. I am looking at different types of rounds and there are a ton of different grains they come in. I am looking for some pro/cons in the 150, 165, 180 grains. Any experience with them as well as factory loads reviews. I'm looking for something that will be flat and accurate around 1200 meters. All input is appreciated