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Posted: 12/24/2008 11:45:33 AM EDT
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Just noticed recently when I was shooting some groups with my flip up sight... I'm shooting much higher with the irons than with my eotech (Eotech is zeroed dead-on at 50/200 yards). Has anyone else had this problem? I will have to move the front sight post WAY up to compensate for this. Is this correct? Help!
I know the irons aren't perfectly lined up in the pic but the point of impact is noticeably higher than what my buis has me aiming at. http://i513.photobucket.com/albums/t336/bpm08a/P1010618.jpg |
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I'm shooting right on, and because of the angle of the pic, it would seem that it's a little left but it's not. But the front sight post would almost need to move up 3/4 of the way to the top of the side posts in order to be at point-of-impact.
AR is a Bushmaster and rear sight is Troy, but i would never think that mechanical zero would be this far off |
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Quoted:
I'm shooting right on, and because of the angle of the pic, it would seem that it's a little left but it's not. But the front sight post would almost need to move up 3/4 of the way to the top of the side posts in order to be at point-of-impact. AR is a Bushmaster and rear sight is Troy, but i would never think that mechanical zero would be this far off Maybe I missed it somewhere in your post, but have you actually live-fire zeroed your iron sights? You can't expect your iron sights to shoot point of aim equals point of impact with just the mechanical zero settings. |
| Yes I have, I shot groups at 50 and they were so far up, I figured I would zero at 25 since my backup sights aren't going to be for long-range shots of course. Even at 25 my groups were 2-3" high, but consistent. It's enough height to be hard to judge accurately if I needed to make a tough shot. I haven't moved the sight post yet because I thought I would draw from the endless pool of knowledge here first.... |
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Just guessing, but from your post is sounds like the buis is new, and your previous rear sight was shooting right on, as well as your eotech? Difference may be a non F fsb which was right for your previous buis, but not for the new one. Think the difference is the F fsb is .04" higher than a non F, which would make up the difference in your current sighting. Again, this is just a guess.
Beware though, more and more, companies are not marking thier F height fsb's as such. Got a caliper you could measure with to verify? Going off memory here, so take it with a grain of salt and verify through a search, but I think the non F fsb is 1.90" high where the F fsb is 1.94" high. Might be something to check. |
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That sounds very plausible, but I don't have calipers to measure. The AR is relatively new as I bought it in June. F or non-F, I'm probably going to have to raise it if it's going to be zeroed with my flip-up sight, correct?
I have noticed that the post on a Troy Front post sits higher in the sight than the stock AR post does: http://www.troyind.com/Images1/frontM4.jpg |
| Yes, you will have to raise it, or purchase a new front sight post that is taller. I believe they are pretty cheap, like $5 or so from multiple vendors. Looking at the Troy front sight as a comparison, or any other sight, doesn't mean much as you would need a size refrence to see if the ears matched up to the overall height of the standard F type FSB. |
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You may or may not find that raising the sight post enough will keep the detent from engaging the base of the post so it rotates freely. Your milage may vary, so give it a shot. If the detent still holds the post from rotating, run with it, if it doesn't, then look to getting a longer post.
This is all speculation at this point though, go shoot the thing, raise the post enough to zero at 50 yds and see what happens. |
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