To determine if lug setback exists, you need to perform a test on the action. With the bolt stripped and inserted in the action and closed, fasten a dial indicator to the action and the indicator pointer touching the back of the bolt. With a free hand, try to move the bolt fore and aft in the action and look for movement of the indicator needle, Do this with the go gauge inserted. Next, with the bolt partially opened (hopefully over any unaltered action lug surface) and notice if there is any movement or note the difference in the two indicator readings. What this will do is show if there is a step in the action lug surface. Confusing? Sorry
