I'm shooting a 300 Winchester mag. factory chambered Savage varmint rifle with a muzzle brake
. I've came up with a load that shoots 6 1/4" @ 820yrds. I'm shooting the Hornady 208grn. A-max "Awesome B.C. rating" over 71gr. of IMR 7828 with CCI large rifle primers. Not Magnum primers it made a difference in my groups. I'm getting about 2800 fps. I shot an 8 point at 560 yards last year and he didn't take a step the bullet performed well. good luck.