Check your action screws for tightness too. Run a piece of typing paper under the rear tang to see if it's correctly floated. As stated check mount screws AND ring screws for tightness. The ring screws need to be snug to hold the scope from slipping in the rings but not "gorilla tight" to the point it may screw up the internal adjustments. In the long run, the factory stock may need to be bedded too. Are you shooting three shot or five shot groups? Five shot groups will heat up the sporter barrel to the point groups will open up quite a bit. Three shot groups are usually the norm for a sporter barrel and I would wait at least two minutes between each shot.

It appears your rifle prefers the Hornady but something is keeping the rifle from shooting to it's full potential. If you contacted Savage about your problem, they would probably tell you 1.5" groups are acceptable and well within their accuracy parameters.