This morning I got up at 5 AM (gotta beat the heat here in Arizona) and headed out to the range. I was shooting at 1000 yards with an AR-30 in .338 LM. I got the windage and elevation set up on my NXS, and was doing ok...not great enough to win any competitions, but most of my rounds were hitting inside the black with one which I got in the "X" ring. Then everything went south. I would fire two rounds, and the second one would be completey on the opposite side of the target out of the black with no wind. A few days ago, I marked with pencil on the scope body where it sits in the rings. I checked the markings, and the scope had not moved. I checked knobs on the unimount, and those were still tight also. I shot a few more, all with the same results. At this time the sun had come up and was starting to get really hot so I figured it was just me and not the rifle, and packed up. As I was putting the scope covers back on, I noticed a rattle. The rail mount thats bolted driectly onto the reciever had come loose. Then it all made sense. With hearing protection, I never heard it rattle around while I was still shooting nor did I feel it rattle. So, tomarrow, I'm going to loktite (the blue kind) everything down, and make sure everything is torqued right. Hopefully it wont happen anymore.