4u,
Try it at 50 yards before you move out to 100. The problem doesn't sound like it's with the rifle... unless the scope mounts are loose. I would put a box or 2 through the rifle and get comfortable with it. Recoil shouldn't be a problem with the .308, a lot of the time it's just form. First, make sure you have a clean barrel...run a bore brush (I prefer the Boresnake) down it to loosen up the crud and then let it soak a few minutes with solvent or foaming bore cleaner. Run a few patches (or the Boresnake) through until they come out clean. Once the barrel is clean, fire 4-5 rounds through with at least a minute between shots (since it is summer) and let it cool for at least 10 minutes. Brush it out again and repeat the sequence. You should see your groups tighten up significantly. Again, the choice of ammo is of utmost importance. Once you sight in with a certain brand of ammo, if you shoot another brand or even different bullet weight, you will have to resight for that certain brand...most are not interchangeable. For instance, I went from Remington Core-lokt 150s to Winchester Balistic silvertip 150s and the point of impact at 100 yards shifted almost 3" high and 4" to the right. As far as bullet choice, I use a 150gr Winchester Ballistic Silvertip (around $20-25 per box)with excellent results on deer, although almost all manufacturers put out a good choice these days. Winchester Failsafes are also excellent bullets but they will cost you apr $30 per box. Good luck and let us know how it turns out.