RE: Glass bedding
Glass bedding helps stop the stock from heating up,,(causing the wood to expand).It also stops moisture from entering the stock,which would result in the same problem,expansion of the stock.If the stock is too close to the barrel,and either of these problems occur,,then the stock will expand ,touching the barrel,resulting in the rifle not holding point of impact.As for tightening of the barrel bolt,,i have a Mod 70(pre 64),that would only shoot well if the bolt was loose.So try tightening AND loosening the bolt(screw) and give it a try both ways and see what happens.