Results 1 to 9 of 9

Thread: Excessive high/low elevation causes?

  1. #1
    Join Date
    Jun 2006
    Posts
    9
    Feedback Score
    0

    Excessive high/low elevation causes?

    I have run into an issue with a rifle shooting far too low. I have spent some time seraching for an answer and asking those I consider knowledgeable on the AR-15/M-16 platform but have not really gotten an answer to my question.

    So here is the basics:

    Both rifles I have run into this problem with are builds. Barrels were installed and torqued to the proper torque.

    Build #1 is a 20" M16A1 clone with an A1 upper and the A1 small dual peep and round A1 front sight post. I flipped the sight to the long range peep and attempted to sight in from the prone at 25 yards. The rifle shot exremely low (I believe it was 6+ inches low, but it was several months ago). I adjusted the front sight to the point where it bottomed out on the sight base, and the rifle just barely started shooting on the bottom of the bullseye.

    Build #2 is a carbine with a midlength barrel, A2 front sight post, and a bolt-on carry handle. This one doesn't have the extreme issue of #1, but still shoots quite low, and the front sight post had to be dropped to within a few turns of bottomed out to get it on the bullseye (carry handle was set to proper notch and peep prior to sighting at 25 yards, just to cover all the potential questions). Although it is "workable" and within the range of the front sight it does concern me that two rifles seem to shoot low.

    I should also mention I have a staright 16" M4 carbine clone (My very first AR, which I purcahsed during the ban). It is a factory built DPMS carbine with 16" barrel and an A1 upper receiver with an A2 peep. This one is dead nuts on at 25 yards and did not take any radical adjustment of the front site.

    So, my theory is one of two things:

    1. Something about my shooting stance/sighting position is causing the issue. However, if this was the case, why is there no issue with the postban DPMS carbine? One would expect that i would have to adjust the front sight until almost bottom out on this one too(?)

    2. Something is amiss with the builds. The only explanantion I ever could get was "maybe you torqued the barrels too much on installation" but I am sure they are torqued properly. I don't remember seeing anything in my armorer's manual covering this issue, and could not think of another soution short of filing down the front sight post, and it seems that doing that is nothing more than a "band aid" to a larger issue.

    I looked around and didn't see any FAQ covering this. My hope is that some of the more knowledgeable folks here might be able to help me out and give me a bit of guidance.

    Thanks,

    Dawg180

    P.S. I did not see a spellcheck...please forgive my spelling errors and look at the content of the post. I injured my wrist a week ago and typing is a bit difficult.

  2. #2
    Join Date
    Jun 2006
    Location
    12S VA 868 817 (NAD83)
    Posts
    1,502
    Feedback Score
    0
    Not sure if you checked this or not, but the first thing I would look at is if your are using one of the "tall" front sight post... these are designed to use a standard FSB with a flattop upper receiver.

    I would have to rule this out before going on to anything else.

  3. #3
    Join Date
    Jun 2006
    Location
    Florida
    Posts
    354
    Feedback Score
    0
    Make sure you are using standard posts. The post on the left is the correct height. The Bushy on the right is for carbines using non F marked sight towers. If you use the taller post on a rifle that does not need it, you will have the problems you describe.

    Last edited by Boom; 06-19-06 at 08:06.

  4. #4
    Join Date
    Jun 2006
    Location
    Colorado Springs
    Posts
    1,857
    Feedback Score
    0
    deleted

  5. #5
    Join Date
    Jun 2006
    Posts
    9
    Feedback Score
    0
    I will double check this on the midelgnth carbine. I was not aware of the different front sight post issue. I will check the FSB to see if it is "F" marked and measure the front sight post this morning.

    This still does not explain the issues with the 20" A1, which has the round 5 notch front sight post, but at least it is a start.

    Dawg

    [ETA] I just checked and the midlength has a .270" front sight post and a non 'F' makred front sight base (the barrel and front sight base are Rock River in origin, double checked by the code stamped into the barrel under the handguards.)

  6. #6
    Join Date
    Jun 2006
    Location
    Colorado Springs
    Posts
    1,857
    Feedback Score
    0
    Quote Originally Posted by Dawg180
    I will double check this on the midelgnth carbine. .....
    [ETA] I just checked and the midlength has a .270" front sight post and a non 'F' makred front sight base (the barrel and front sight base are Rock River in origin, double checked by the code stamped into the barrel under the handguards.)
    Then you ought to be shooting high with that combo. In fact, you ought to be unscrewing the front post so much that you'd be able to see daylight under the post's base.

    Who made your carry handle, do you think it's up to snuff? Do you have any other BUIS's around you could swap out and test?

  7. #7
    Join Date
    Jun 2006
    Posts
    9
    Feedback Score
    0
    It is a DPMS carry ahdnle, and I don't have another BUIS at the moment to try out. Good thought, though- I'll see if a buddy has a BUIS I can borrow for a week or two and see how things work out.

    Another good question...any way to "reset" the elevation adjustment on the rear A2 sight? I'll leave that until after testing some other BUIS, but it might be a solution. My temporary solution the day I originally took it out to zero and forgot my sight tool (fell out of the bag, doh!) was too crank the rear elevation to the '4' setting and it was dead on at 25 yards.

  8. #8
    Join Date
    Jun 2006
    Location
    MD
    Posts
    50
    Feedback Score
    0
    Dawg,
    '4' is the right setting for 25y, so you're good to go there.


    If you used the 'L' marked peep sight on the A1 then there are 3 things that come to mind. (in order of likelyness).
    1) You are using the carry strap as a hasty sling or you are using another kind of sling to stabilize the barrel when you shoot. This pulls down on the barrel and will make it hit low.
    2) Barrel is bent (test with a straighness gauge).
    3) Upper is machined incorrectly.

    Hope this helps.

    -Forest

  9. #9
    Join Date
    Jun 2006
    Location
    Colorado Springs
    Posts
    1,857
    Feedback Score
    0
    Quote Originally Posted by Dawg180
    It is a DPMS carry ahdnle, and I don't have another BUIS at the moment to try out. Good thought, though- I'll see if a buddy has a BUIS I can borrow for a week or two and see how things work out.

    Another good question...any way to "reset" the elevation adjustment on the rear A2 sight? I'll leave that until after testing some other BUIS, but it might be a solution. My temporary solution the day I originally took it out to zero and forgot my sight tool (fell out of the bag, doh!) was too crank the rear elevation to the '4' setting and it was dead on at 25 yards.
    I recommend you go to the tacked thread on Improved Battlesight Zero (IBZ) on the Optics and Mounts board. Make note of the modifications to the procedure if you are setting your carbine RCH that maxes out at 6/3 (-4 clicks). Otherwise, it's set up for a fixed A2 sight (8/3, - 2 clicks). Also note that it is 50 yd based rather than 25. But once you are set for that, then it will be easier to figure out what's going on with your situation.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •