I aqiured a Striker in .308 from a relative who passed away. It looks and functions great, but I am just not to sure about it. First of all, I can't hit the broad side of a barn with it. Second, it does rattle my teeth. I have shot it from a bench (incorrectly), and that hurt, then I shot it offhand, both hands on the grip, and I shot a three shot group of 5 inches at 25 yards, then I used a set of shooting sticks from 100 to 35 yards, and couldn't get on the paper. I like the fact that it was my uncle's a lot, but if I can't be effective with it, then I won't really enjoy it. I am an avid shooter with lots of experience with different guns. Guess I need some advice, I am pretty sure I am doing it wrong. Thanks for any suggestions.

scope is a Burris 3x7, shooting 7.62 bulk rounds.