i want to buy my hubby a new scope for his ar, he has had it a long time. He wants to shoot 3 gun and I know they shoot out to 450 yards. His eyes aren't the greatest so he needs something really good. The clerk at our sports store recommended a burris 1.5x6 I believe. Any recommendations would help please. Also, would a 3x9 be a more powerful scope which he also recommended. thank you