RE: Caliber Selection
It sounds to me like the guy didn't have much experience with rifles and, that being the case, I would NOT have recommended a magnum caliber. I would have suggested a .270, .280, 7mm-08, .308, or .30-06. Any of those would do the job at reasonable ranges using the correct bullet.
Everyone's tolerance for recoil is different. A .300 Magnum, for what appears to be a first "big game" rifle, is a surefire way to create a shooter who flinches...