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Rib Height Mathematicians

Discussion in 'Shooting Related Threads' started by loophole, Jan 10, 2010.

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  1. loophole

    loophole TS Member

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    Gentlemen:
    Disregarding the pull of gravity and assuming that a projectile shot from a gun with a rib exactly parallel with the barrel will impact exactly the rib height low on target.
    Now, how much in thousands of an inch, will you lower the rib height at the front of a 30" barrel to raise the point of impact one inch at 30 yards. I'm assuming that you multiply that by 2 for two and 3 for a three inch raise in impact.
    Now if your barrel is 32" long do you multiply Answer A by 32/30 to achieve the same impact? Or 34/30?
    Now if the point of impact is at 35 yards would you multiply Answer A by 30/35? 40 yards by 30/40?
    How much will gravity drop a #7 1/2 pellet at 35 yards? Any charts available for this measurement. Awaiting a mathematical genius for the answers. Loophole
     
  2. Unknown1

    Unknown1 Well-Known Member

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    Pardon me for asking but... why even worry about one inch unless you're Phil Kiner?

    MK
     
  3. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    It's proportions and ratios that will tell you what you need to know. 25 yards equal 1080 inch's divide your 30 inch barrel into 1080= 36 times. Divide 36 into 1 which equals 1 inch rise, you come up with .0277 of an inch. So if you stuck a .0277 shim under the back of the rib, your point of impact would be 1 inch higher, or removed that much from the front of the rib would be doing the same thing.
     
  4. acss

    acss Well-Known Member Supporting Vendor

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    for simplicity, i,ve always went by- 1/8" = 4" at 30yds-- whether thats true, i'm not exactly mathmaticly sure-- but is does work for me when setting a comb or rib!!
     
  5. Onceabum

    Onceabum TS Member

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    I was sitting in the clubhouse one day working on that very important problem and missed my squad.

    BB
     
  6. Neil Winston

    Neil Winston Well-Known Member

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    It's more complicated than it looks; this covers all the important considerations. The pellet falls a little less than 3 inches at 35 yards.

    Neil
     
  7. Dr.Longshot

    Dr.Longshot Banned Banned

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    If you keep the same sight picture and every thing the same before you shoot and the same making the sight picture adjustments, for approx every .030 you lower the fron bead or raise the rear of the rib, you will raise the POI 1 inch. If you want to raise poi 4 inches raise the rib in the rear .120 to .125
    of an inch, I have had to raise POI 12 inches in the past and I had my rib professsionally cut on my Ljutic by Jimmy Ljutic .375 to achieve my POI, this can only be done on some guns, others have to be re-ribbed.

    I know several people that shoot a POI os 30 inches at 30 yards, now that is high. Ray Stafford shoots a high POI gun.

    The only really high shooting trapgun out of the box w/no alterations is the Caesar Guerini Un-Single, I know of no other gun that shoots this high including K-80 Special or Kolar Max. Have patterned them.

    The Caesar Guerini Full Choke Tube produces a 19"inch pattern at 40 yards, I have the pattern to prove it. I don't say all of them will do it but my past 2 did produce that pattern.


    Gary Bryant
    Dr.longshot
     
  8. Dr.Longshot

    Dr.Longshot Banned Banned

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    The pellet drop does not even enter the calculation if you pattern your gun and you want to raise the POI 4 inches you raise the rib in the rear .125, you are still shooting the same shell, same shot size, and the same distance.
    POI will raise accordingly, plain and simple there are no other variables.

    Gary Bryant
    Dr.longshot
     
  9. Neil Winston

    Neil Winston Well-Known Member

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    Gary, if you raise the rib at the rear - and that's all you do - nothing about the POI will change.

    Neil
     
  10. Dr.Longshot

    Dr.Longshot Banned Banned

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    Raising the rib at the rear has the same effect as lowering it in the front, But you have to change the sight picture, the steeper the slope from rear to front bead raises Point of impact, If you doubt it then Jimmy Ljutic and I had a magician bending my barrell w/o our knowledge. If you raise the rib 1 inch in the front and 1 inch in the rear you will have the same POI.

    Take a MX-15 Perazzi to shoot higher with a center of the rib pivot point, take it 4 notches down in the front and up 4 notches in the rear it will shoot 12 inches higher, eack notch+ 3 inches, it says so in their owners manual,

    If you leave the front bead alone and raise the rib in the rear you are doing the same thing, raising Point of Imapct.

    I should know I have done it numerous times.

    I think if you re-read you will come to the same conclusion.

    Gary Bryant
    Dr.longshot
     
  11. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    Gary, If you raise the front of the rib and the rear of the rib 1 inch, the gun will shoot 1 inch lower. If you do the same only 6 inch's this time the gun will shoot 6 inch lower.
     
  12. hmb

    hmb Well-Known Member

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    If raise the rear of the rib, and keep your eye in the same position, you will not be able to see the front bead. Unless you have xray vision. Do you understand what I am saying. Neil does. Right Neil? HMB
     
  13. wayneo

    wayneo Active Member

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    Your eye is the rear sight on a shotgun. You need to move your eye up or down. Wayne
     
  14. racer

    racer TS Member

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    Longshot- you must have gotten 20 & 40 mixed up on the tape measure or you only used a 19" target. Who you trying to kid? Dan
     
  15. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    What confusion that rear rib adjustment has had on a whole bunch of people!!! In my view, the rear of the rib should merely rotate with adjustments done at the front, either up or down. If the comb isn't moved, the only change in POI can come through the front of the rib being raised or lowered. If set at the lowest notch and the gun needs a higher POI, the comb must be raised. Reversed for a lower POI with the front of the rib all the way up.

    Hap
     
  16. Dr.Longshot

    Dr.Longshot Banned Banned

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    If you create a greater slope, the rear of the rib higher than the front bead the POI will raise proportionately, approx .030=3 inches.

    Well 1 inch increase in height front and rear w/shoot 1 inch lower, true.

    Neil if you take a Ljutic One touch and slide it forward it shoots higher, same principal as raising the rib, the part closest to your eye up it will shoot higher, with same sight picture as the eye is the rear sight.

    On my first Ljutic a LTD-2000 Denny cut my posts off decreasingly from the bead to the ramp, ramp height stayed the same, It was an 80/20 POI gun I took it to 100% high shooter, he cut the front post off about .090 and tapered back up the posts and had to braze Mat'l for the rib to slide into where the grooves were gone so the rib would stay attached to the Bbl.


    Gary Bryant
    Dr.longshot
     
  17. racer

    racer TS Member

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    Longshot- lets see that pattern you talked about earlier in the thread. Dan
     
  18. Ted K.

    Ted K. Member

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    I think Dr. Longshot is assuming that the rib pivots near its center. Some guns do that (Perazzi) other don't (Kolar).

    If the rib pivots near its center, raising the rear of the rib will lower the front bead. But if the rib pivots near the rear, then moving the rear of the rib up or down (possible only by making some major change in the structure of the rib mount) will have no effect on the height of the front bead above the muzzle, in which case the movement at the rear of the rib will not affect the POI.

    I am assuming that the comb (and thus the height of the shooter's eye) is not changed through out all of this.

    Ted K.
     
  19. Dr.Longshot

    Dr.Longshot Banned Banned

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    Lets do this with another gun, the Browning POI adjustments is at the rear of the rib, closest to your eye, you raise the rib in the rear and you have to raise the comb to get same sight picture, your POI raises proportiantly.

    I had one of the first Browning Adjustable rib combos.

    If you leave the front sight at the same height above the Bbl, and raise the rear of the rib closest to your eye you have to adj comb to get same sight picture you raise the POI.

    Now you take a Beretta Gold E un single w/adj rib, and you lower the front of the rib that has the front sight attached you are accomplishing the same thing.

    If you raise the rib by adding a paralell rib to the top of the existing the POI will only change by the thickness of the add on rib which is negligble
    you won't notice it unless you are shooting a rifle.

    The invention of the adjustable rib ias and was a major improvement in trapshooting to get the POI to each individuals preference.

    Ray Stafford is the perfect example of shooting a high point of impact gun and his RS models of Perazzi shotguns, some RS guns are not adjustable rib guns, just high ribs to get you to shoot with the head in a more upright position which should help deter raising your head to look at the target.

    A shooter can determine how high he wants a gun to shoot at the pattern board shooting off a rest, Pattern the gun as is on a spot on pattern board.
    Now put a small piece of Balsa Wood an inch long on top of the rib closest point to the eye but on the rib itself, adjust your comb up to get same sight picture, and fire the gun again off the rest and see how much you raised to POI from the previous shot. If you think that is what you want shoot a few targets on position 3 w/trap set on straight aways and look at your breaks, make these adjustments until you get the target centered, now you can have a rib maker build you a rib or have an adjustable rib with the same dimensions and the capability to go higher, Because as you get more profecient, the average shooter will gradually gravitate to a higher shooting POI.

    It has been said that 70-90% of the shooters shoot a gun that shoots too low for them, from my observation of new shooters this is true, they will shoot under the targets, and braks will be low and pieces go up when broken.


    Gary Bryant
    Dr.longshot
     
  20. hmb

    hmb Well-Known Member

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    Gary,

    Read your last post. Now you are adjusting the comb in addition to the rib. HMB
     
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