GaryW,
With Double Rifles, improper bench technique can cause targets that make it seem that the rifle dosen't shoot as well as it really will. Try normal 180 gr loads and this time hold the rifle in both hands, raise the front rest so you have to sit upright,and fire the right barrel followed by the left as quickly as you can get back on target.Let the barrels cool to ambient temp. barore shooting the next right/left.When you shoot a cool barrel next to a warm one the target looks bad.
Mike