Lets say you have even contact on your locking lugs because youve taken the time to lap them in. Whats to say that the face of the bolt head is strait with the bore?
The proper way to lap in the locking lugs is to first true the bolt face and the rear of the locking lugs so they are square or concentric first. After that the action needs to be straitened (all actions are crooked). If the actions crooked/twisted/bent but the locking lugs are strait you still are pushing more against one recoil lug than the other knocking the face of the bolt off.