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How far do I drift the front sight?

Discussion in 'Gunsmithing and Repairs' started by tcoz, Jul 7, 2018.

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  1. tcoz

    tcoz Member

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    My Sig P320c has a 6 inch sight radius and after installing a new front sight POI is 2 inches left of POA at 22.5 feet. If possible I'd rather not use the trial and error method to drift the sight since I live about ten minutes from the range and could conceivably involve multiple trips back and forth.
    Does anybody know a formula that I can use to figure out how far to drift it and also if anybody has any tips on doing so I would appreciate it. I have a sight pusher tool so that part isn’t a problem.
    Thanks in advance guys.
     
  2. drband

    drband Member

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    I would just center the front sight on the slide (measuring with a caliper). The front sight could be off such a tiny amount you might not be able to tell by visually inspecting it.
    If it is precisely mounted (centered), then adjust the rear sight for windage.

    Shoot off a rest to test and get someone whose skills you trust to shoot it before moving the rear sight.
     
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  3. 98bluewave

    98bluewave Member

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    Don't know of a formula but a gunsmith showed me how he adjust sights and it works for me. Make a pencil mark on top center of the slide in front of the rear sight. Also make a mark on the sight that lines up with the mark on the slide. I use a soft pencil which makes a fairly wide mark. To move the sight 6", I would move the rear sight the width of the pencil mark. If that's not where it needs to be you can see exactly where the sight was before you moved it. You may have to make one more adjustment but this method works well for me.
     
  4. Chuck R.

    Chuck R. Member

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  5. MEHavey

    MEHavey Member

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    About 44 thousandths. =2*6/(12*22.5)

    Go measure the diameter of a standard paperclip (~30-thou) to calibrate your your eyeball.
    With sharp pencil, mark along side of the existing sight if possible, or sight center point (both sight & slide) if necessary.
    Drift sight (left) about 1-1/2 paperclips using mark as reference
     
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  6. JTQ

    JTQ Member

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    Don't most folks center the front sight and drift the rear sight?
     
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  7. tcoz

    tcoz Member

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    I don’t know whether it really matters. I replaced the front sight so I figure the rear was already properly positioned and I’m trying to basically return to the original POI although it was shooting about 1 inch left before I replaced it.
     
  8. Deus Machina

    Deus Machina Member

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    Good tips.
    Otherwise, why run back and forth?
    If I think I need to adjust sights, I take a sight pusher or hammer and punches to the range.
     
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  9. 1911 guy

    1911 guy Member

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  10. 4v50 Gary

    4v50 Gary Moderator Staff Member

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    Clamp the supported slide in a vise. Put a piece of brass stock in the chuck of your drill (or quill of your mil). Touch off (no power) and then press slightly. If it's a mill, I'd raise it with the knee.
     
  11. Col. Harrumph

    Col. Harrumph Member

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    It’s a simple question of proportion. You’ve measured your sight radius and found it’s six inches. Your target was 22.5 feet, or 22.5x12=270 inches away and the POI was off by two inches. So the problem reduces to, what fraction of 6 inches equals that fraction of 270 that is two inches? Expressing the question mathematically:

    X/6 = 2/270

    Solving for X: X=2*6/270 = 12/270 = 0.44 inch. So that’s how far you need to drift the sight (same answer, front or rear).
     
  12. tcoz

    tcoz Member

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    Should be .044 inch, right? Wow, just over 1/25th of an inch...not much.
     
  13. tcoz

    tcoz Member

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    Thanks to everybody for your help. It looks as though I’m gonna be taking my sight pusher and calipers to the range. Getting the sight drifted 0.044” will take some trial and error.
     
  14. MEHavey

    MEHavey Member

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    Believe me:
    Think 1-1/2 paper-clip/eyeballed... and you'll be fine
    (post#5)
     
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  15. MEHavey

    MEHavey Member

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  16. tcoz

    tcoz Member

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    Thank you. I missed that the first time through.
     
  17. Shimitup

    Shimitup Member

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    If you measure the thread pitch of your pusher it will tell you movement per rotation. For example a 1/4 28 is 1/28 = .0357, I don't own a sight pusher but I would be surprised that they don't provide instructions to that effect. To me .044 seems like a lot, surprised you don't see front or rear way off center without relying on measuring tools.
     
  18. drband

    drband Member

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    I would be interested in how you solve your sight issue.

    I prefer my front sight to be centered exactly. If you are going to adjust it, you should hope it holds position.

    The reason I center mine (and use red loctite) is that it’s easier to have only 1 variable when adjusting sights for accuracy. I assume your rear sight is a standard Sig sight that is easier to engage with a pusher than the front, so it would be easier to sight your pistol that way once you get the front perfect (measuring with calipers).

    Regardless of how you do it, it can be done either way I guess!
     
  19. Bwana John

    Bwana John Member

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    The differences you are trying to change will be very hard to measure.
    I would do it empirically using 98bluewaves method.

    If the sights do not move after regulating them I like to split the windage difference between the front and rear sight instead of having a big offset on one or the other.

    If the rear sights are calibrated and I intend to change windage when shooting I put the rear sight on 0 and regulate the front sight
     
  20. JohnKSa

    JohnKSa Moderator Staff Member

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    MEHavey got it right. Move the front sight 0.044" (or about 1.13mm) in the OPPOSITE direction that you want the point of impact to move.

    I would shoot at longer distance and make the correction based on the results at a longer distance rather than correcting it based on shooting at only 22.5 feet distance.

    Here's a generalized version the formula MEHavey used:

    Shooting Distance (feet)
    Point of Impact Error (inches)
    Sight Radius (inches)
    Sight Correction (inches)

    Sight Correction = (Point of Impact Error * Sight Radius) / (12 * Shooting Distance)

    To determine which direction to move the sight, use the mnemonic 'FORS'. Front Opposite, Rear Same. That is, when moving the front sight, move it in the OPPOSITE direction you want the point of impact to move; when moving the rear sight, move it in the SAME direction you want the point of impact to move.
     
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  21. 98bluewave

    98bluewave Member

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    I've never had a problem with sight adjustment, except when I lost the rear sight elevation screw on my Buckmark! I've changed out the sights on all my Glocks and for several others who asked me to change their sights. I always center the front sight using a scale, and use locktite on the screw holding the front sight. I also center the rear sight using a scale. If I find I need to make an adjustment, I move the rear sight using the pencil mark method as described above. I've never had to move the rear sight more than about the width of a pencil mark and I typically only have to move the rear sight one time. Good luck, it's a lot more fun to shoot when you hit where you are aiming!
     
  22. Col. Harrumph

    Col. Harrumph Member

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    Yas, 0.044. Good catch!
     
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