I have spoken with a couple of other guys with the same rifle and they were getting about the same results that I am getting. Perhaps it is the ammunition or some issue with the way the rifle is used on the bench. Are the groups fired using sandbags or a padded rest front and rear? How many shots are fired per group? Are the fairly good except for a flier? Are groups normally horizontal, vertical, or just scattered?
It is unlucky that you would get two lemons in a row when most other fellows are getting good results. People generally good products from Winchester (and Remington) in spite of what some claim on the internet. I hope you and your son get this sorted out soon. Do you handload?