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Posted: 3/1/2003 7:28:26 AM EDT
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Here's what's happening: If I start out with the elevation wheel bottomed out, I can see a small gap between the front of the rear sight assembly and the rear of the upper. As I turn the elevation wheel to raise the sight, the little gap stays the same until the 5th click up on the wheel, at which point there is an audible "pop", where the sight assembly is moving forward slightly (where the little gap was), so that the small gap that was there is gone and the assembly now rests against the back of the reciever. Now... if I start turning the elevation wheel back down, I can see that little gap slowly starting to open back up a little with each click of the elevation wheel. It appears that something is forcing the sight assembly backwards during the last 3 or 4 clicks of the elevation wheel. Anyone have any idea what the problem could be? Could it be that the sight assembly wasn't installed properly, or would it be a problem with the upper reciever? Part of me wants to guess that maybe the spring in there might be binding against something. Any ideas? Thanks, Tim |
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Its just torque/tension and a new tight receiver that is causing the difference that you are seeing. When the housing is all the way down, the bottom of the housing is held against the receiver below the sight housing. As the sight housing is raised, the bottom sight housing and receiver tension is released, and then the sight housing can index off the right lip like it is supposed to do. The receiver will loosen up in time, so I wouldn't worry about sending anything back. As for the popping, the sight housing retainer cross pin is catching the sides of the guide slot in the threads and you are hearing it pop when the tension is released. If it really bothers you, you could just remove the entire sight housing from the upper, and take the burs out of the slot on the elevation threads of the housing. As for zeroing the rifle, just raise the housing a few click to allow the housing to index off the upper right rail, and not the receiver below the housing. Dano |
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Hi, Thanks for the reply. This particular upper isn't really "old", but it's not terribly new either. A friend of mine bought it as part of a complete rifle (bushmaster) about 4 years ago, and put probably about 1500-2000 rounds (I'm guessing) through it while he had it. He's never been someone who worried too much with "details" (like accuracy, etc. ;-)... so he may never have moved the sight from the 8/3 position. Anyway, after I got the upper from him I switched barrels and then noticed the problem the first time I went to shoot it. The short term fix I used was the same one you suggested... I just set the drum so that I could zero the rifle with the sight set a few clicks up. After doing that, I took the rifle out yesterday to zero it and I found that I'm now having to set the front sight so high to get it zeroed, that it's starting to wiggle around a little. Not good for zeroing. I think I saw someone somewhere on the net selling front sight posts that are slightly higher than the standard one, but I can't remember where I saw them. I'll probably just do as you suggested and pull the sight assembly and see what I can do as far as de-burring. With any luck that'll do the trick. Thanks for the info. Tim |
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