Sight Problem

Discussion in 'The Powder Keg' started by Cyrano, May 8, 2008.

  1. Cyrano

    Cyrano Resident Curmudgeon Forum Contributor

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    I was at the range today helping to rewire the lights to get things up to code. While we were working, John, one of the members, was trying to sight in a new AR-15. He has others, but wants to set this one up for 3-gun event shoots. It's one of the ones with the Picatinny rail that runs the length of the upper, and while it came with a scope he was trying to adjust a rear peep sight and a moveable front post.

    He couldn't get on the paper with it at 100 meters, so he shortened the range to 50 meters and tried again. He still couldn't get on the paper. When we stopped for coffee, I went over to where he was glaring at his AR-15 and we started chatting. I offered to spot for him though his spotting scope. He said, "I'm so fed up with this gun I could spit. YOU try shooting it and I'll spot for you."

    So I took his place at the bench and aimed at the 50 yard target, a standard NRA 100 meter paper bullseye target. Two rounds aimed at the bull were not on the paper. For some reason he had put a black spotter at 6 o'clock about 3 inches below the black, so I told him I was shifting my point of aim to that, and fired three rounds slow-fire that grouped in the seven-ring at 12 o'clock. There was a rip in the paper halfway between the spotter and the bottom edge of the target. I shifted point of aim again, told him, and fired four aimed rounds that you could have covered with a dollar coin in the 10-ring.

    Now that's a whole lot of Kentucky windage, especially for an AR-15 at 50 meters. John, Louis the Mosin Kahuna and I fiddled with the adjustable sights for 20 minutes and the three of us could not come up with a front sight position that would lower the point of aim enough to get the thing on the paper. Either John needs a new, lower front sight on the beast, or he needs a much taller rear sight to get the rifle to shoot true. I wasn't impressed with the way the aftermarket sights that came with it line up on the rail. Is it possible he was shipped a front and rear sight that are from two different sight sets? And am I right that either lowering the front sight about an inch or raising the rear sight about the same is the correct solution to his problem?

    Postscript: I offered John the opportunity to try Natasha, my Mosin-Nagant 91/30. He accepted, I ran him through the safety, loading with a stripper clip and bolt-closing procedures, and he let off a round. He then tried to take a second shot and nothing happened. He looked at me.

    "I think there's something wrong with your rifle."

    "John, it shoots a little better when you work the bolt, eject the old round and chamber a new one."

    We both laughed. He said he hadn't fired a bolt-action in years, just semi-autos and over & under shotguns. Once he got used to the bolt, he liked the rifle and was astonished when I told him what they cost these days - he's used to paying much more. But then again, he does shoot AR-15s, which cost about 10 times as much as a Mosin!
     
  2. rfc357

    rfc357 Guest

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    If I read this correctly, the rifle is shooting high? If so, to lower the the point of impact, you must raise the front sight or lower the rear sight. Forgive me if I have misunderstood.
     

  3. +1
     
  4. at4rxj

    at4rxj G&G Newbie

    When you say the rail runs the full length of the upper... do you mean over the handguard as well, or just on the upper receiver itself? Does he have a fixed front sight or a flip front sight?

    If he has a flip sight, make sure he has the right one... they make 2 different heights. One mounts on the gas block rail and is taller to match the rear sight, and the other mounts on the handguard rails and is shorter as that rail is higher than the gas block. If he has the wrong one, he'll never get it zeroed.
     
  5. Cyrano

    Cyrano Resident Curmudgeon Forum Contributor

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    rfc, madcrate, at4, thanks for the replies. Further info:

    The rail runs from the rear of the upper all the way up over the handguard.

    The rifle is shooting WAY high. His flip sight is mounted to the rearmost slot in the rail and is a flip-up. I got my results using the target peep sight with the rear sight laid down flat.

    We tried raising the apparent height of the front sight by moving the front sight back toward the rear of the upper, but it did not help. I really think John has the front and rear sights from two different sets of sights here. I have never heard of the sights on an AR being so screwed up you could not get on the paper without using Kentucky Windage.
     
  6. at4rxj

    at4rxj G&G Newbie

    Can you post pics of what he has? It sounds like he either has the rear sight on the wrong plane (like on a riser), or the front sight is the wrong kind.

    They shouldn't be that far off if everything is right.
     
  7. rfc357

    rfc357 Guest

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    Going back to your original post, it still looks like you are trying to correct the problem in the wrong direction. If the gun is shooting high, you must lower the rear sight and/or raise the front sight.
     
  8. Cyrano

    Cyrano Resident Curmudgeon Forum Contributor

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    Hey, all I know is that if it's aimed at the center of the target at 50 yards, it's not on the paper. If you aim toward the bottom of the target, it hits dead center.And that was with the front sight as far forward as it would go. Moving it back along the action (that giving it an apparently taller front sight) should have reduced or eliminated the problem, but it didn't.
     
  9. Actually moving the front sight closer created the optical illusion of the front sight getting taller. What actually happened was the sight plane was shortened and it made it harder to aim. If the rifle is shooting high which from your post it is then the front sight must be actually raised or the rear sight has to be lowered or a combonation of the 2 must occur.
     
  10. Paper

    Paper I can justify anything. Forum Contributor

    I'm new to the AR world, so forgive me if it's a dumb question, but is there a tool needed for raising the front sight?
    I took my CMMG to the range for the first time tonight and even at 50 yards the rifle's shooting around 7-8" high, even with the rear sight bottomed out in the down position.

    Can I just turn the sight up, or is a tool needed.. I thought I'd ask before screwing something up..
     
  11. Most AR post type front sights have a detent that holds them in place. It is spring loaded and is designed so that a 5.56 bullet can be used to depress it and turn the sight. The easiest way is to get a front sight adjustment tool. They are inexpensive and well worth the money.
     
  12. Wingwiper

    Wingwiper Guest

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    There are THREE types of Front sight posts, that I am aware of.

    The OLDER M16A1, 5 position front post and it should have its base at almost dead even with the top of the hole. Use a 6 penny nail to turn the front sight in the direction of the arrow that corresponds with the direction of the bullet impact.

    The Newer M16A2 has a Square 4 position front post and it should be adjusted the same way.

    the British Needle Post, only used it once and threw it away, so can't tell you much about it.

    First off, the plane of the rear and front sights should be somewhat parallel to the plane of the barrel. It sounds to me as if the Rear Sight ramp is seated at too much of an angle and probably needs some machining to get it correct. There may be a burr under it that is preventing it from seating fully down on the ramp.

    If you need to adjust by that much, there ain't much, other than filing that you can do to the front site post and I would only take off about 1/8" the most. The rear sight mounting is where I am sure the problem is at. Unless you have a bent barrel.
    For 50 yards My AR-15 is 1click from bottom on the Rear and his center. If you can NOT achive this, your mounting is faulty..
     
    Last edited: May 15, 2008
  13. Cyrano

    Cyrano Resident Curmudgeon Forum Contributor

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    John's AR-15: A Follow-Up

    I ran into John down at the range yesterday and asked him if he'd ever gotten the bugs out of that AR he was setting up for three-gun competition. He chuckled and said, "Yes, I did, and you aren't going to believe this.

    "The problem was with the gas tube. The one on that AR is proprietary. It's just a little taller than the standard tube. That means that if you try to use anything other than their propritary front sight, which is shorter than the other aftermarkets to compensate for the difference in their proprietary gas tube, it won't shoot to point of aim. I bought a new set of sights from that company, and now it shoots just fine! Stupid, isn't it?"

    I had to agree it seemed mighty bizarre. But he let me try five rounds out of it and I put them into a group you could cover with a quarter, so I guess it turned out all right in the end.