I just bought my first Nightforce a few weeks ago and I have a small issue. I was returning the elevation turrent back to its zero setting and it stopped clinking and began to free wheel. Upon further investigation, the knob just pulled right off the scope. It is not a zero stop and I bought the scope used in what I thought was great condition. Has anyone ever had or heard of this happening or am I freaking out way to soon? Any advice would be helpful. Thanks!!