AH, check out the rate of twist in the barrel, you'll need to have at least 1 in 10 or tighter to shoot 120 gr bullets in it, but 100 or 115 gr Nosler Partitions should be reasonable pig pills, unless as was suggested you're up close & personal. At 303/25 velocities 1 in 10 is getting marginal to stabilise some of the 120gr bullets out there.
Steve