Just my take. I had issues shooting light rifles from the bench. Found I had the snug them up a bit more than my standard wt. rifles or the groups would open up. Agree that some say, and some find, thinner contour bbls like some pressure. Before you go pulling anything apart, try shooting and snugging the rifle in a bit tighter to your shoulder. Make sure you're only pulling back, not putting any pressure down on the stock. If that doesn't help, then I'd look at the bedding and floating or making sure you don't have any unwanted pressure points.
