If bore scope looks good I would ask about how tight the barrel nut is. Then I would ask about the stock. Is it pillar bedded? Are the screws torqued? Out of all of the cartridges you shoot, the 300 WM is a hammer. Are you sure you are not flinching. Use a video camera to tell. My son could shoot anything but when behind a lightweight 7mmRM he looked like a girl. A video helped him out.