some rifle barrels when machined get choked at the breech due to the pressure applied when the barrel is turned to fit the breech block. Put a pellet into the barrel and push it to the muzzle end, if it's loose at the muzzle then thats the problem. As mentioned check the crown with a Q tip,any fuzz left there will tel you the crown is bad. Tighten the cross screw for the pivot pin if loose. Check the lock up ball and lug for any dirt in the area, clean and relube. Shoot the rifle with the scope off and using iron sights, if the problem is still there then it's not the scope. Watch how you hold the rifle with the scope on and with the scope off, a different head position will apply more or less pressure to the stock also watch how the hands touch the rifle with and without.