A few inches behind the flash suppressor is a stamping of the 308 caliper on your thin barrel. Check inside the barrel to see that the stamping has not transferred to the bore. If you can see a dimple there send the rifle back to S&W. Barrel is no good and will never shoot accurate when it deforms the bullet because of this problem. There is another post on this subject with pictures.
S&W needs to make a recall on this problem. The suggestions by folks on this thread indicate very few folks seem to be aware of this problem.