.300 Weatherby seems like overkill for deer. But if he can handle it I guess it would work. Too much noise and recoil for me. I am partial to the 6.5x55, have been shooting that caliber all of my adult life. I even used a custom-made Douglas barreled Mauser in 6.5x55 for bench rest shooting back in the late 60s-early 70s. Over 30 years ago I was speaking with a Swedish national. According to him, that's by far the most popular hunting cartridge in Sweden. And with good reason.