300 win mag ammo

[berjerkin]

was just at the range this afternoon plinking around and now seem to have a problem. i sighted in with 150 gr. federal premium speer soft point, cheap factory stuff. dialed in to 1 inch group at 100 yards. opened another box to check at 200 yards and was shooting all over the place, barley keeping the group on the papaer. went back to shooting at 100 yards and same results, all over the place. maybe just got a bad batch of shells or somthing, but i should probably step up to some better ammo. what would you recomend? i only chose 150 grain due to only antelope and whitetail tags this year. i hear 180 gr. are best for a 300. let me know what is accurate.