I'm so bummed. My last cheap scope died today. The worse part, I knew it was gonna happen before I even started shooting.
I have gone through (now) 5 scopes in 2.5 years on my AR10's. I had 2 SASS and now my DMR. The average cost of the scopes was about $250. Every single scope I put on any AR10 would work great for 2 trips to the range. On the 3rd trip, it would fail to hold zero. Happened every time. I am guessing its the jarring recoil... but who knows.
I have had a Nikon P223 on my M4 for a year or more. Made dozens of trips to the range. It never missed a beat, ever. A few months ago I got a new EOTech with a magnifier for the M4. So, I moved my P223 scope over to the AR10 to finish the DMR build.
Well, just like always... today was trip number 3 to the range with that scope on my AR10. As you look at the image below, you will see that my first 3 shots all hit the bullseye. By the time the 20th and final round hit the paper, it was 6 minutes high off center (100 yards). You can see how the grouping very rapidly fell apart.
I guess its time to pull out my big boy pants and buy a real scope. I just really thought this would have been the one.

http://fiveguysracing.com/marc/Gun_Stuf ... Breath.jpg
