RE: Sighting In Problem....
If they didn't put blue lok-tite on the base screws they should have. As far as overtightening, you don't want to crank it down with an impact wrench, but you don't want any play in them at all. Get them good and snug.
Also, make sure that you are letting your barrel cool suffiecently between shots. A lot of the time, your groups, or in your case "patterns" will be in straight lines. IE: The bullet's point of impact will "walk" or "string" in a direction. Make sure you give it at least 10 minutes between shots. Bring a .22 to pllink with, or a good book to kill the 10 minute lulls, but don't cheat.
Beyond that, you might have a bedding problem, but if it is in the scope, it should be pretty easy to fix, and based on what you have told us, I would blame the scope. Take it back.