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POI

Discussion in 'Shooting Related Threads' started by capt kirk, Jul 22, 2010.

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  1. capt kirk

    capt kirk TS Member

    Joined:
    May 25, 2010
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    I know this is probably rehashing an old thread but here goes anyway. If a gun was shooting say 60/40, how much would the comb need raised to make it shoot 100% high? what is the common equation for figuring how much 1/8 or 1/2" will raise POI?
     
  2. Bob Schultz

    Bob Schultz Well-Known Member Supporting Vendor

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    Jan 29, 1998
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    Location:
    Tuxedo NC
    To raise the POI to 100% you would need to know the distance (within an inch or two..) between the bead and the shooters eye on the particular gun. Lets make it easy and say its 36 inches or 1 yard. So, for each sixteenth of an inch you raise the comb (or the shooters eye) you would raise the POI 35 yards away 35 sixteenths or 2 1/8 inches.

    Therefore, to raise the POI to 15" or 100% high, and the gun was already shooting 3 inches high(60/40), you need to go up 12 inches or 192 sixteenths so divide that by 35 or 5.48 sixteenths = 11/32"

    On this particular hypothetical gun the math is easy... Most trap guns with 34" barrels put the bead to eye distance at about 40 inches. The longer this distance is the more you need to raise the comb. With 34 inch barrels I use the general rule that each 16th of an inch will raise the POI 2 inches at 35 yards. This will get you close, then pattern and fine tune.

    Hope this helps. Bob Schultz
     
  3. zzt

    zzt Well-Known Member

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    Capt, I use the same method as Bob, but I convert it to POI per spacer so I don't have to do math every time I want to play with POI.

    There are 45" between my eye and the front bead. I divide the distance I am interested in by 45" to get a multiplier and go from there.

    For example, at 40 yards (1440") there are 32 eye/bead units (45" for me). 1440" / 45" = 32. So at 40 yards, any change you make to the comb will be magnified 32 times.

    For a 1/8" spacer that comes to 4" (0.125" x 32 = 4"). A 1/16" spacer is half of that (0.0625" x 32 = 2").

    4" at 40 yards is 3" at 30 yards, and 2" at 20 yards. So just by remembering that (for me) a 1/8" spacer moves POI by 4" @ 40 yards is enough. If I want to raise POI by 8" @ 40, then I'll add two 1/8" spacers under the comb.

    All I have to remember is that at 40 yards, a 1/8" spacer moves POI by 4", a 1/16" spacer moves POI by 2", and a 1/32" spacer moves POI by 1".
     
  4. JTEA

    JTEA Member

    Joined:
    Jul 13, 2007
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    367
    Location:
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    Ljutic One-Touch monoguns have settings to change the rib angle equivalent to 10% increments. Standard rib adjusts from 60/40 > 100 over. They include corresponding spacer washers to raise your comb, one washer per 10 % increment. The washers are 1/16" thick. You would need 4 washers @ 1/16" = 1/4". Get some 1/16" washers and start the trials!

    The rib is really an optical device for the eye, the two real factors are the front bead and the eye in the rear (comb height). If you "get it right" you may want to order an add-on rib, try making one from balsa wood or pine first.


    JT
     
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