My dad's old Leupold, 6x fixed, has been dropped off a horse landing on a rock in Colorado, dropped from a deer stand in Texas, and basically has been worn and torn but it has never needed to be re-sighted. And this dates back to the '70's. He checks it every fall and still on target. He once said he hasn't seen the adjustment knobs in years, hasn't had to. I killed my one and only mulie in '89 with it at approximately 370 yards. A little hold over and an effective lung hit. Hard to beat that that durability.