My 308 with 168eldm does about the same thing. Good to 1000 and then all over the place. It has done 5 shots into .5 moa at 1000 with good conditions. After shooting the 308 the 6.5-06 with 147s almost feels like cheating. My AR10 308 with 20" barrel and 168 Amax is good to around 800 maxLocal range only goes to 340, with 600 every other Sunday. I try to make it out every weekend but that's not feasible anymore. However, lately I've been able to do cold bore shots to 600 on the 10, 6, and 4 inch plates with my 6.5cm which has felt gratifying.
I took my .308 to a range about 4 hours away for more distance than we have here. I kept up with the pack shooting steel from 200-1000, but 1050 and beyond my .308 fell flat on its face and went from holding 1moa to about 10moa. I'm guessing bullets were tumbling when they went transonic. My buddy was able to hang on to the mile target with his 6.5, which sold me on getting one for myself