My long-range scope was a Leupold Mk 1 Ultra 16X It was part of an extra order for 50 cal. scopes used by the Navy. The lenses were glued in as the original intention was to use them on the semi-auto Barrett. The folks at Crane figured out that the Barrett kicked both ways so the scope lenses had to be protected , they were glued in. If a lens ever broke, it could not be fixed. I was lucky and used for many years with a sling at 1000 yard matches on my .300 WM bolt gun. It worked great and I didn't get sea sick watching my crosshairs. I have it on a tactical M1A.