If you're an experienced reloader. And you've been able to get a Ruger to give 1/2 inch groups, I would trust your experience, and suspect the gun has a defect.
Check all the usual suspects with a revolver. Cylinder lock up, throat diameters compared to bore diameter, forcing cone integrity, cylinder gap.
Then call the manufacturer. For $1700 I would hope they stand behind their product.
Some other questions: When you shoot a group, do you shoot the entire cylinder? Is the group that large as a whole? Or do you have 3 or 4 clustered together with the others flying wide?