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Posted: 5/16/2014 12:52:34 PM EDT
| First off I don't think the rail is the issue. I had it on a different upper and it fit fine. Just got a new barreled upper today and went to install the rail and right away noticed that the fit of the rail between the upper and the barrel nut was very snug. The rail is touching the receiver at the top as well as the bottom where the front lug is. But it's on there. Problem is if you look at the barrel where it comes out at the end of the rail, the barrel is not centered inside the rail. And because the rail is so tight against the receiver, I can't push the rail over any to center things up. As it sits I think it will have excessive windage and not zero. Has anyone run into this? Shouldn't there be at least a very small gap between the upper and rail? |
| Not much, 2mm. Doesn't seem right that the rail contacts the upper solidly top and bottom. I have two other Centurions and both have about a .020 gap. This gives you some wiggle room to get the rail straight. I did some more checking, I think the barrel nut is the issue. The one on the upper measures .825 front to back. Two others that I have here measure .854. And from the rear of the barrel nut notches (which is what the rail butts up to) to the back of the nut is .690, while the other nuts I have are .725. |
Here are some pics. First three are before pics, you can see that the rail is slammed up against the receiver top and bottom, so there is no room to adjust it side-to-side or up-down either. Last pic is after i put on a new barrel nut. Now it has a small gap like it should. However I'm noticing that the rail is sitting below the top rail of the receiver, and now it trails of at a slight upward angle. That seems to indicate that the reciver threads aren't 100% straight in relation to the centerline.
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This could possibly be related to the receiver and not the rail. The upper receiver and rail may be true, but the barrel may be canted from the receiver face being ever so out of spec. Where the barrel extension and receiver meet may be slightly off angle. This would lead to extra barrel offset typically noted by being off center.
Might look into getting the Brownells receiver lapping tool. That would true the receiver face and then everything should be straight. |
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I agree that it is not the rail. I never really suspected the rail as it had been on another complete upper and fit fine. The first issue was the barrel nut, but now with that part being fixed there seems to be an issue with the receiver. I actually thought lapping it might fix it, but being that it's brand new I might swap it out.
Quoted:
This could possibly be related to the receiver and not the rail. The upper receiver and rail may be true, but the barrel may be canted from the receiver face being ever so out of spec. Where the barrel extension and receiver meet may be slightly off angle. This would lead to extra barrel offset typically noted by being off center. Might look into getting the Brownells receiver lapping tool. That would true the receiver face and then everything should be straight. |
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