Frontier Gander has agood suggestion when he says to try using the open sights.

If you can get a consistent grouping (somewhere) on paper with the open sights that would definately point you toward the scope/scope rings. It might also eliminate a stock/receiver/projectile issue. But as others mentioned, I would try other projectile and propellant combos.

Set that target to 50 yards so it is nice and easy to sight in on with the open sights and see if you can get a consistent group.

You are bench shooting right, not firing from a standing position?

It sounds like you better pack a few sandwichesfor your next trip to the range, you might be there for a while! But there are worse things in life

Best of luck. It is frustrating when you have problems, but as I'm sure you know, that is how we learn.