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Posted: 1/5/2011 4:37:11 PM EDT
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Here's the archived thread: The gist of it was that I had bought a used upper with a Sabre 18" SS Grendel barrel. The previous owner claimed 1 MOA or better. I had taken the rifle apart when I received it, put it back together, and had AWFUL accuracy. I swapped optics, swapped muzzle devices, thoroughly cleaned it, and torqued and retorqued the barrel nut - all in vain. I even bought a barrel vise, thinking that the use of an action block was not the best way to install a barrel (even though I'd built another 1 MOA 5.56 carbine using just an action block for barrel installation.) As it turned out, that was more true than I imagined. The strangest thing was that it had a weird tendency to shoot a nice 3-shot group at first, then open up to an awful 7" at 100 yards. I now know why... I've just returned from the range and I'm happy to report that the rifle is shooting 1 MOA groups. I'm happy with that performance. How did I fix it? I had the barrel locked in the barrel vise, and had the upper receiver snugly (but not tightly) secured in the action block. I wanted the action block to index the upper as I torqued the barrel nut. As I was torquing the nut, I suddenly noticed that the nut was impinging on and compressing the action block, and not fully capturing the barrel flange. So all this time I'd been torquing the nut to 50 ft.-lb., but not torquing the nut to the receiver at all! I dremeled the face of the action block so that the nut would have clearance, and voila! |
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