I would start by chronographing your loads ,if the standard deviation
is over 20 ft/sec this could be your problem.
Next thing that I would look at is the position of the bipod or sand bags.
If they are to far out on the forearm then this could be the problem.
Bedding or lack of could also be causing this problem.
Last but not least is trigger control (To heavy,creep or inconsistant grip control.
Thats all I can think of to start with.
J E CUSTOM