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Question on taper of rib

Discussion in 'Shooting Related Threads' started by 7571, Dec 24, 2008.

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  1. 7571

    7571 Well-Known Member

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    Does anyone know for sure how much taper is needed in a rib for a gun to shoot a full 15" high (or 100% if you prefer) at handicap distance? Meaning sighting straight flat down the rib, not elevating your eye higher than the rib and looking over the middle bead.

    I'm meaning the amount in relation to the center line of the bore. Does something around 11/16" difference from rear to front sound about right?

    This would be in the 31" sighting plane of a 34" barrel.

    Thank you,Tom
     
  2. Neil Winston

    Neil Winston Well-Known Member

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    Tom, unfortunately, it can't be calculated without knowing what the present POI is, not for sure, anyway. Roughly speaking, it should be about 0.52 inches (but check that*) my calculations, but it could be upset by the gun not shooting straight down the bore, which happens a lot. You have to find that out first.

    Neil

    * Others will correct me if I'm far wrong, and if so, I suspect zzt will get it right; he's got all this at his fingertips.
     
  3. 7571

    7571 Well-Known Member

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    Hi Neil,

    Thanks for responding. What I was meaning not to change a point of impact, but rather what relation to the center line of bore assuming the barrel is perfectly straight shooting.

    What I wanted to know if there is a known drop from rear to front that will tell how high above point of aim a barrel shoot at say 40 yards.

    All this considering the rise of shot and the drop from gravity.

    Thanks again,,Tom
     
  4. phirel

    phirel TS Member

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    Tom- I think you are talking about projecting two straight lines to 40 (1440 inches) yards and then adding in the 3 inch fall due to gravity at 40 yards. If you want a line to go up 15 inches at 1440 inches, in relation to another line, it must go up 0.0104166 per inch of travel at a club where there is no gravity. If you shoot at a club where there is gravity, you have to have the line project to 18 inches high (3 inch gravity fall) to end up with 15 inches high at 1440 inches. That means the line must rise 0.0125 inches per inch of travel. On a 30 inch rib, this would be a difference of 0.375 inches along the length of the rib.

    If my calculations are wrong, please blame that on my calculator. It was on sale at Wall Mart for $1.

    Pat Ireland
     
  5. 7571

    7571 Well-Known Member

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    Pat,

    Thank you for the math lesson, I had forgotten all that in the 48 years that I left school. You are probably correct on your calculations. I thought around those same dimensions before, but it just don't seem to work that way for me. It seems more like 5/8 to 11/16" for me.

    Again, thanks and have a very Merry Christmas and Prosperous New Year,,,Tom
     
  6. Neil Winston

    Neil Winston Well-Known Member

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    Psst! Tom! (Whispered) Listen to Pat.

    Neil
     
  7. 7571

    7571 Well-Known Member

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    Neil/Pat,

    Thank you both.

    Again, Merry Christmas and Happy New Year.

    Tom
     
  8. Gary Waalkes

    Gary Waalkes Well-Known Member

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    Let me walk out on to this rather thin ice and just say that calculations and or static POI test results may not mean anything once you mount a gun and say "pull".
     
  9. Bob Hawkes

    Bob Hawkes Well-Known Member

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    And there Gary, is the problem! What the heck happened?? LOL Shoot well and often while we can, Bob
     
  10. 635 G

    635 G Well-Known Member

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    3/4"----5/16"---this is what Dennis DeVault uses on his Elite conversions & Infinity guns-this config---will give you 100% or 15"

    Lou
     
  11. mixer

    mixer Well-Known Member

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    Am I correct in assuming that with a flat non adjustable rib gun the only way to change the POI is to change the comb height?


    Eric
     
  12. phirel

    phirel TS Member

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    Eric- Changing the comb or bending the barrel is the only way. I have done both.

    Pat Ireland
     
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