I have been a member, and match competitor in the Fifty Caliber Shooters Association (FCSA) since 1992. I have used both the NF Benchrest series and NXS series, and the S&B PMII 5-25 on competition .50 bolt guns, & prone/tactical semi-auto and bolt .50's (Barrett M107A1 & the Navy Mk15/McMillan TAC-50). I have also used a Kahles 6-24X on a DTA HTI. All were sturdy enough to hold up reliably. Many people do not realize it is not the recoil or muzzle blast that causes the reliability problems of scopes on .50's. .50's are like piston air guns. It is the "reverse" recoil that occurs that shakes things loose inside the scope. Scopes are generally designed to withstand normal "rearward" recoil. The muzzle brake on a .50 causes up to a 21 g reverse recoil shock wave to the scope (Eric Williams did the experiment and wrote an article on it in the VHP in the early 90's). Many scopes in the past did not have internals designed to withstand this. In the late 80's and early 90's, the Leupold Mk4 Ultra series was the only one that consistently held up. After Jeff Huber listened to requests/needs of FCSA competitors, Nightforce first released the benchrest series scopes in the Mid 90's, and later the NXS series, both of which have set a track record of holding up well. Now there are probably many others that will hold up, but there are still many that may not. I have no reliability concerns when using either NF or S&B's on my .50's. A look at the "equipment lists" of the top competitors in the match reports will give you an idea of what they trust and use. Personally, I would also not hesitate to use the Kahles or Steiner tactical series scopes either. As Jester308 stated, just be sure to have a quality set of rings or mount. And recheck the torque on all the screws frequently the first several times you use the rifle, as they tend to "shoot loose." Once everything is settled in, they usually stay tight.
Scott
