I would have a gunsmith or someone very knowledgeable about rifles check it out. It could a worn, loose or defective part in the action. Another posibility is something isnot tight/rightbetween the barrel, receiver, action, gun to stock, bases or rings. Is this rifle suppose to be bedded or free floating - if so is that part okay? Is the stock sound? How does the rifling look? Is it pitted or worn? How does the crown look? Is the barrel bent in any way? Is the trigger pull so high it is hard to be accurate? I had a rifle like this - so I adjusted the trigger (make sure you know what you are doing here or have a gunsmith do it for you). Personally, I don't shoot from a vice as you may crack the stock (I shoot from a rest).Is there a hairline crack in the stock from when you bought it? Some peoplehave reallyloading up their Lead Sleds - it is possible the person knew they cracked the stock and traded it in. It could also be a gun that needs to have handloaded rounds to be accurate.