Sounds to me like the barrel is not true with the receiver, or the base is tilted back on the receiver. You can either replace the current base with a 20 or 30 MOA rail or shim and bed the base you have (my preference because it's cheap). Can you have the gunsmith who built the rifle fix it?
If not, inspect the base by removing the scope and rings. Place a steel straight edge across the top if the base and see if the surface is flat. If the straight edge rocks back and forth the base is bent, and that was likely the culprit. You will have poor fit with a new base as well. If the base is not bent, the barrel is probably not true to the receiver.
Either way, you should bed the base to get a good fit to the receiver. If you stick with the current base, you have to shim the base at the rear attachment point, which is easy. Cut brass shim material to fit around the rear mounting hole. I usually cut the shim in a "U" shape. You need .025-.030" thickness. Four layers of beer can will work in a pinch. Then bed the front and rear of the base using JB Weld. Look for videos online on bedding a base. Make sure the bedding material gets in between the shim layers.
During epoxy set, torque the rear base screw to 10 in lbs (to compress the shim sandwich) and the front screws to 2 in lbs (no more or the base will deform). After the epoxy sets, you can torque the base screws to the usual values (about 20 in lbs).
Good luck.
