Recently acquired an AR-15 (Colt Match Target HBAR in case it matters). I am in the process of adding the bi-pod, quadrails, etc. what i am not as familiar with are the quality of the optics. I would like a Variable zoom scope that could take me to he weapon's effecive range need be. I know you get what you pay for when you go cheap. Is there anything in the $300 range that wou be effective and quality over 300 yards. I know the guns max effective range is approximately 550 yards.