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Posted: 6/24/2009 12:02:41 PM EDT
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I recently got to fire my CMMG 14.7" upper for the first time and I seem to be having problems with it. It is a flat top with an ARMS 40L and standard F marked FSB. With the sights zeroed out at the beginning the rifle was firing high and to the left of point of aim. To get the rifle to remotely fire at point of aim at 50 yards we had to adjust the ARMS 40 all the way to the right and still have not properly zeroed it. From visual inspection by several individuals, the barrel and FSB don't appear to be canted. I'm going to pull the barrel sometime today to inspect the indexing pin. Is it possible the problem could be fixed by lapping the front of the upper and reassembling? Even with the windage all the way to the right it is still short of point of aim and groups terribly.
Thanks |
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Before pulling the barrel, make sure the rear sight is centering on the upper rail, hence mount the sight backwards, and bore sight the rifle again.
As for the barrel, confirm that you are not getting bullet strikes off the FS first, then maybe slip the barrel in the upper barrel socket instead of pulling it to see if you can get the sights to bore sight with the barrel. But yes, if the upper barrel socket is not square with the upper bore line and the barrel is not warped, then socket lapping will resolve such. To add: if you do pull the barrel, confirm that the barrel extension pin is on the same plain as the FSB. If these are not on the same plan, having bullet strikes to the FS, or the barrel is warped, then you could be in for more trouble than it's worth, and the barrel needs to be sent back for replacement. |
| Thanks for the reply. I believe I have found and corrected the problem. The FSB WAS canted about 2 degrees to the right. If my thinking is right, the 5 good whacks with a hammer I gave it should at least help to correct the windage problem. To my eye and hand it looked and felt like the barrel moved in the right direction. If I can move it with a hammer I think its important I re-torque the barrel just to be sure. |
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