Iron,
One other thing you need to consider is intervening brush. Assuming that the rifle and scope are ok, and that you made a "good" shot,a small branch can really send the bullet astray. Regardless of the nonsense you hear and read about brush bucking calibers, "THERE AIN'T NO SUCH THING". Any bullet can be deflected by brush, and it doesn't take much. I grew up in Pa. and started with the quintessential Pa. deer rifle the .30-06 pump with 180gr bullets. I shot many deer with the 180, and did quite a bit of target shooting over various ranges with it. There is no way that a rifle sighted at 100 yds. would exhibit enough trajectory difference to miss a chest shot at 80 yds--uphill, down, sideways, or inside out. But, hit an unnoticed piece of brush...