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raising the comb x amount=how much diff in poi ?

Discussion in 'Shooting Related Threads' started by kevin a., Jul 4, 2011.

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  1. kevin a.

    kevin a. Member

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    about how much added comb hieght adds 6" of poi ?

    thanks kevin
     
  2. Unknown1

    Unknown1 Well-Known Member

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    On average, raising the comb 1/16" raises the POI at 30 yards by 2 inches.

    MK
     
  3. timb99

    timb99 Well-Known Member

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    It depends on a couple of factors.

    What is the distance, when your gun is mounted, from the bead to your eye?

    At what distance do you want this 6" change in the center of your pattern?

    Is it a fixed rib or an adjustable rib, and if adjustable, will you adjust it (this opens up a whole new can of worms)?

    If it is a fixed rib, do you understand that you will no longer get a "figure 8" sight picture, but will most probably be seeing a lot of rib between the beads?

    OK, if we assume your eye is about 36" from the bead, and if we assume you want that 6" change in your POI at 35 yards, the answer is approximately 3/16 of an inch.

    BUT, you should only use this as a starting point, and check it on the pattern board.

    X = ((change in POI in inches) x (length from eye to bead in inches)) / ((yardage you want the poi change) x (36 inches per yard))
     
  4. BigM-Perazzi

    BigM-Perazzi Well-Known Member

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    I like the short answer lol...
     
  5. timb99

    timb99 Well-Known Member

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    BigM

    Ha, ha. Yeah...I chose the "rigorous" method.

    Its a throwback to those days of college engineering courses where you had to "show your work."

    But the short answer is just as right as mine.
     
  6. mixer

    mixer Well-Known Member

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    I question if 1/16" actually does anything considering the amount of give in a face and the cheek pressure applied to a comb.


    Eric
     
  7. fssberson

    fssberson Active Member

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    I have the same question. If I raise the comb 1/8", how much down range yardage does it raise/lower the POI. I have lost weight, especially in the face and my gun's POI became almost 2' floating of the target. Changed the washers [larger][Dennis Devault colored washers] by one color and the POI seemed to flatten out by a foot. No longer shooting over targets... dead center/6" below target = 50 straight yesterday. Fred
     
  8. timb99

    timb99 Well-Known Member

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    <i>I question if 1/16" actually does anything considering the amount of give in a face and the cheek pressure applied to a comb.</i>

    Eric,

    If you mount the gun the same way and apply the same cheek pressure as you did before you made the change (and accept the fact that you see more rib), your POI will move. By calculation, 1/16" will move the POI up by 2" at 30-35 yards, but as I said, you need to check it on a pattern board to see what is reality.
     
  9. Unknown1

    Unknown1 Well-Known Member

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    <blockquote>"I question if 1/16" actually does anything considering the amount of give in a face and the cheek pressure applied to a comb."</blockquote>OK... MATHEMATICALLY a 1/16 inch rise at the comb will result in about a 2" rise in POI...

    But if you have a flabby face that swallows up that comb rise in fat displacement, REALISTICALLY just stock up on spacers and experiment until you get what you want!

    MK
     
  10. 1brucem

    1brucem TS Member

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    The question seems to me to be wrong in it's inception. One raises or lowers the point of aim to center targets not some conceived and forced perception that a 70/30 or 80/20 p.o.i. is what you should shoot. It doesn't matter what that per cent is and you will find that with every gun, trigger, weight, length that the percent is different for you. What matters is centering targets and use that as your guide. Bruce
     
  11. Unknown1

    Unknown1 Well-Known Member

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    The guy simply asked how much he had to raise a comb to raise the POI 6 inches.

    It's a simple question.

    His motives for asking it are irrelevant.

    Just give the guy a simple answer.

    MK
     
  12. kevin a.

    kevin a. Member

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    A Change in Comb Height (inches) 0.1875

    B Comb to front sight (inches) 42
    Change A, B or C to
    C Distance to target (yards) 41 determine change in POI

    D Change in POI (inches) 6.589285714



    1/16 0.0625
    1/8 0.1250
    3/16 0.1875
    1/4 0.2500
    5/16 0.3125
    3/8 0.3750

    sent buy tada1 to me - thanks
     
  13. kevin a.

    kevin a. Member

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    Point of Impact (POI) Calculation


    A Change in Comb Height (inches) 0.1875

    B Comb to front sight (inches) 42
    Change A, B or C to
    C Distance to target (yards) 41 determine change in POI

    D Change in POI (inches) 6.589285714



    1/16 0.0625
    1/8 0.1250
    3/16 0.1875
    1/4 0.2500
    5/16 0.3125
    3/8 0.3750







    this was sent to me by tada1 from this site- thanks ted








    kevina_2011_17044.jpg
     
  14. Unknown1

    Unknown1 Well-Known Member

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    Before some of the seriously out-of-shape get stiff necks from the physical exertion of trying to read sideways... <center>
    [​IMG]
    </center>

    MK
     
  15. chipking

    chipking TS Member

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    Thanks MK that really helped.


    chipking_2008_030359.jpg


    --- Chip King ---
     
  16. pullll

    pullll Member

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    This is somewhat related to this thread but concerns head/eye positioning.



    Next time you are at the patterning board cheek the EXACT position of your face/eyes including, pitch forward, left/right pressure on cheek, view through shooting glasses exactly same each shot.


    I feel that is why short neck vs. long necked shooters seem to have an advantage. The long neck shooter has a very wide range of rotating motion, probably more than six. Up/down, twist, tilt, shoulder/cheek distance.


    I have found myself snugging up tighter to the stock after a miss just to make sure I smoke the next target. I have changed all the parameters from the norm.


    Tough game,
    shoot well.
     
  17. fssberson

    fssberson Active Member

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    Pattern Board vs Actual Gun Placement on the Target. I will take pattern board for the horizontal BUT take actual gun on target for the vertical. Why?
    Because for an experienced shooter you know where you want the gun to be in relation to the target. I don't want to adjust to the gun, but the gun to adjust to me. After 40 years, I know where I want the end of the gun to be in relation to the target whether raising or dropping. The horizontal needs to be dead on for every shot so the pattern board will tell you how much bend to put on the barrell from your car bumper. Fred
     
  18. 9point3

    9point3 Well-Known Member

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    Take a look at this, remember all values are in inches

    http://www.brownells.com/.aspx/lid=13093/GunTechdetail/Sight_Correction_Calculator
     
  19. bluedsteel

    bluedsteel Member

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    In my experience, moving the comb or the rib has minimal effect on point of impact for many shooters. Unfortunately, shotguns are not like rifles, where moving the rear sight or scope reticle has a profound effect on where the rifle bullet impacts the target. Yes, in theory, raising the shotgun's comb raises the point of impact, just like elevating the rear sight on a rifle raises the bullet's point of impact. However, in practice, this is not often true with the shotgun.

    There are many reasons for this. One of the main reasons is when shotgun shooters shoot a moving target, they are focused on the target, not on aligning a front and mid bead (if there is a mid bead on the shotgun in question).

    True, the beads may be aligned almost like rifle sights (in a figure eight, or similar), when the shotgun shooter calls for his clay, but at that point everything you know about rifle shooting (and thought you knew about shotgun shooting) goes out the window. Hence, the mystique of learning to shoot a shotgun well.

    bluedsteel
     
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