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How does comb adjustment affect POI

Discussion in 'Shooting Related Threads' started by Rollin Oswald, Jun 11, 2009.

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  1. Rollin Oswald

    Rollin Oswald Active Member

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    Please refresh my memory on the effect of comb adjustment on POI. Assume a 30-inch barrel on a repeater.

    Thank you.

    Rollin
     
  2. Neil Winston

    Neil Winston Well-Known Member

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    Raise the comb and you raise the POI. A sixteenth of an inch at the comb is two inches at the bird, more or less. And more or less is all the closer you have to be.

    You can shift some sideways too; that's to line your eye up with the rib.

    Neil
     
  3. Rollin Oswald

    Rollin Oswald Active Member

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    Thanks, Neil. That's exactly what I needed to know.

    Rollin
     
  4. BDodd

    BDodd TS Member

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    If we assert that our eye is the rear sight on a shotgun then raising or lowering the comb will raise or lower the rear sight and, thus, the POI up or down. Same with left or right, move sight left or right and thus the POI left or right.....breakemall....Bob Dodd
     
  5. rick979

    rick979 Active Member

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    Rollin: If you didn't know the answer to this question I suggest that you change your email address....fast!!
     
  6. Rollin Oswald

    Rollin Oswald Active Member

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    I'm familiar with the concept and the reason behind it but did not remember the numbers considering a 30-inch barrel and am not mathematician enough to figure it out.

    Rollin
     
  7. shannon391

    shannon391 Active Member

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    I know this has been talked about much but what does 4" high at 13 yrds translate to at 40 yards?
     
  8. hmb

    hmb Well-Known Member

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    12" high at 40 yards. HMB
     
  9. shannon391

    shannon391 Active Member

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    Thanks HMB,

    What % high would that be called.
     
  10. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    shannon, you'd need to tell us what diameter the pattern was at 40 yards to know the %......
     
  11. shannon391

    shannon391 Active Member

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    AT 13 yards it was 2"

    That should be a good morning exercise for you math guys.
     
  12. Rollin Oswald

    Rollin Oswald Active Member

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    I'm happy to see that my ignorance has been a learning experience for others.

    Rollin
     
  13. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    [AT 13 yards it was 2" ]

    Well Shannon, If the pattern was 2" @ 13 yds, and we surmise it's 6" @ 40 yds.

    And you said it was 2" above Point Of Aim (POA) @ 13 yds, which means it was 6" high @ 40 yds.

    <IMG SRC="http://www.google.com/images?q=tbn:DK16EOJ0nrQLfM::www.thenutritionacademy.com/images/calculator.jpg"

    then the percentage would be 200% above your POA.

    (I think)
     
  14. gun fitter

    gun fitter TS Member

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    Rollin ROFLMAO!

    This is a trap!

    Moving a comb does not change the impact of the gun.

    How one references the muzzle relative to the bore line is the real question.

    On a pattern plate this works since most shooters aim the gun.

    On targets it is trial and error since some shooters look over or parallel with the bore and others look down at the rib.(Advanced fitting 201)

    Joe
     
  15. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    Betcha...
     
  16. Neil Winston

    Neil Winston Well-Known Member

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    Big M swooping in for the easy money again before the rest of us can get our bets on the table.

    I'll tell you, Joe, if you are fitting people with stocks and don't think that where the comb is relative to the bore has an Influence on the POI I wonder what you think does.

    Neil
     
  17. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    I'm sorry Neil, forgot about the Seniority clause...

    Let me have the crumbs....
     
  18. gun fitter

    gun fitter TS Member

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    Even Rollin knows what I'm referring to. Unfortunately you don't Go back to ballistics where you're an expert.

    Joe
     
  19. Neil Winston

    Neil Winston Well-Known Member

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    While you are right that I'm no expert on stocks, Joe, if comb-position really does not affect POI the a whole bunch of adjustable-comb stocksmiths are selling fairy dust. And I don't think they are.

    I'm glad to see that you do accept that at a pattern board and aiming, the POI does move. How can you use a pattern board without aiming? What do you shoot at if not "something?"

    Neil
     
  20. gun fitter

    gun fitter TS Member

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    This is where experience helps in fitting. For some shooters the rules do not apply. There seem to be two types of shotgun shooters that are effected by this differently. I'll call one pointers and the other aimer's. Now few are absolutely one or the other. Some rely quite heavily on eye hand coordination Pointers and the other use vision and aiming.

    Think about a perazzi adj rib. Without moving the comb aswell you may have done little to effect shot placement.

    Some pointers seem to be less influenced by movements in comb height at least initially. These shooters are looking over the gun and allowing memory and coordination to steer the gun to the correct position. For some of these shooters pitch seems to be critical and seems to effect the impact relative to line of vision.

    Now for an aimer all the conventional rules seem to apply most of the time and indeed moving the comb will effect the point of impact when shooting targets. These shooters also will see no change in impact when shooting different pitches. Recoil may change but there will be little or no change in impact on a pattern plate or on targets.

    I hope this helps or at least points out the complexities and relative lack of absolute rules which can be applied.
     
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