GUN let's talk AR front sights

Discussion in 'On Topic' started by spankaveli, Nov 18, 2009.

  1. spankaveli

    spankaveli OT Supporter

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    i currently have A2 sights on flat top uppers. therein lies the problem.

    so my current options are to replace the A2 front sight with either F-marked sight, a flip up sight or a railed gas block and a flip (or fixed) sight on top of that.

    opinions? post pics and links if possible. :o

    here is a picture of the upper in question. i have two that are identical and both have thesame problem.

    [​IMG]
     
  2. The issue with the F vs. non-F FSB is merely that the F raises up the post a tiny amount, so it's properly aligned with the rear sight on an A3/A4 receiver. If you try to zero the elevation of a non-F FSB with an A3/A4 receiver it's possible you run out of upward travel on the front sight post and basically unscrew it. To fix this you can do any of the thing you've mentioned, or you can simply buy a slightly longer sight post. I know there are a few places out there that sell longer ones specifically to remedy this A3/A4 w/ non-F FSB problem.
     
  3. spankaveli

    spankaveli OT Supporter

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    You're right, that is the problem. My other problem is that I'd prefer to not have my post past the ears on my base which is where they are/will be. A longer post will not resolve that issue.
     
  4. You could have included that in your initial post.

    The required height of the post is directly related to the height of the rear aperture. It shouldn't need to stick above the ears. If it does, there's something else going on. If you go to an aftermarket setup you'll have the same problem because they're all designed to fit a standard height, unless you find something with exceptionally long ears.
     
  5. spankaveli

    spankaveli OT Supporter

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    That post you listed is .03" higher. The shelf on an F-marked base is .04" higher. Obviously the higher shelf would resolve the issue and it's my understanding based upon info I've read elsewhere that this will correct the issue while not needing the post as high as it is relative to the base's ears.
     
  6. spankaveli

    spankaveli OT Supporter

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  7. Soybomb

    Soybomb New Member

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    I wouldn't worry about a .04 height increase on the post. Go grab your calipers and look at just how tiny that is. Its a cheap upper, appreciate it for it is and don't double your investment in it over such a trivial issue.
     
  8. As I understand it, the overall height of the FSB is the same regardless of its "F status." The relationship of the top of the post to the top of the ears is the same whether you're running a F FSB or a non-F one with the longer post.
     
  9. spankaveli

    spankaveli OT Supporter

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    The height of the post in relation to the base has it literally "hanging on by a thread." There is actually space between the bottom of the flat part of the post and the top of the shelf of the base.
     
  10. sprite

    sprite Active Member

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    Will the irons be the primary sight system? If not I'd just cut down the FSB, install an extended length handguard and run flips on it.
     
  11. spankaveli

    spankaveli OT Supporter

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    I had that same concern (and soybomb's about the .04 not being significant). Check the two links.

    I'm not sure exactly what the problem is but my thought process is this:

    Two different upper manufacturers = can't blame it on that
    Two larue rear sights = probably can't blame it on that

    That only leaves me with the base or the post. As uneducated as I am on the subject, I feel as though if I get a taller post it will still be at the same height relative to the ears on the base.

    That leaves me with the base. I don't believe that would fix the issue either but I can't argue with people on two different sites who are suggesting the same thing...
     
  12. Quib and Molon are right in the M4 thread, and they're saying the same thing I'm saying.
     
  13. spankaveli

    spankaveli OT Supporter

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    Can you find me an extended length railed handguard that is relatively the same weight as m4 carbine handguards?
     
  14. spankaveli

    spankaveli OT Supporter

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    I suppose it wouldn't hurt to try the taller posts. I did see where they said that was the obvious fix (and I agree, that was my first thought) but if Quib is saying that he used a taller post and it was still within "ear height" then maybe that is the case. :dunno:
     
  15. The distance from your bore centerline to the top of the post has to be a certain value to achieve a zero at a certain distance with a certain rear sight. That value can only change (and keep the zero the same) if you change the height of the rear sight. Since the F and non-F bases are the same overall height it shouldn't matter which one you use, so long as your rear sight is within spec. With the slightly lower platform on the non-F you will have to have commensurately more of the sight post sticking up to achieve that specific over-centerline value, but that should be the only difference, the relationship between the top of the sight post and the top of the ears will not change whether it's F or non-F. If you're in a situation where you actually have to have the post sticking above the ears of the FSB, then I'll put my money on there being something that's out of spec.
     
  16. sprite

    sprite Active Member

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    Not your personal shopper brosef, just making a suggestion.
     
  17. spankaveli

    spankaveli OT Supporter

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    So I've either got two Larue rear sights that are out of spec or two uppers (of different manufacture) that are both out of spec or two front sight bases.

    Right?
     
  18. spankaveli

    spankaveli OT Supporter

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    :ugh:

    I figured I'd ask if you knew of one.
     
  19. You'll have to investigate. Either the non-F with the taller post or the F with a standard post should zero without the top of the post sticking above the ears. If that's not the case, then something's not right. I can't help you by speculating as to what it is over the internet.
     
  20. spankaveli

    spankaveli OT Supporter

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    I think I'll just order two taller FSP's and if they don't stick past the ears I'll stick to them and if they do I'll come back to this thread and re-ask which route to take to replace the base. :rofl:
     
  21. eWRXshun

    eWRXshun hai

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    OT: who local can take off my perm attached phantom and replace it with another perm attached phantom, just with a quick detach and replace the FSB while its in their hands at the same time?
     
  22. How is it permanently attached? Is it soldered or pinned? If it's pinned all you need is someone who can carefully grind the weld holding the pin down, let the pin fall out, unscrew the FH, drill the new one for a pin, screw it on, drop a pin in, weld the new pin in, and then clean it up. You'll have to use some kind of coating like one of those bluing pens or paint or something to protect the metal. It's really a pretty simple procedure. I did it to my own rifle. If you want to be in strict compliance with the law, just make sure your lower (assuming it's a rifle lower) isn't around when you do this.
     
  23. spankaveli

    spankaveli OT Supporter

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    I spoke to the friend who recommended this barrel, he called Tiger and told him about my problem (since tiger uses these barrels) and tiger told him he's never had issues using LaRue uppers & DD rear sights. My friend has a couple DD rear sights on the way. I'm going to try one of those before I go changing parts around.
     
  24. eWRXshun

    eWRXshun hai

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    its pinned/welded.

    i have access to the tools and equipment to do it myself but honestly, if someone local can do a good enough job and keep it clean, $30-40 isn't a problem for me to drop on having an experienced professional do the job and not have to call in favors to use a drill press and welder around someone else's free time.
     

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