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Adding on to Rib, what happens?

Discussion in 'Shooting Related Threads' started by chuckles, Feb 28, 2010.

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  1. chuckles

    chuckles Member

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    My gun shoots a POI of 60/40, maybe 65/35...

    what happens to the POI if I add a 5/16" high Rib to the top of the existing Rib...???

    Chuck
     
  2. goose2

    goose2 Well-Known Member

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    If you add a rib that is the same height at both ends the POI will not change. If you have a slight taper down at the muzzle end it will raise your POI. The taller rib will give you a more heads up mount on the stock.
     
  3. chuckles

    chuckles Member

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    TinMan, I want to lower my POI, I want to shoot dead flat or 50-50...
    I have an adjustable comb and it is as low as I can get it.

    regards
     
  4. Ajax

    Ajax Well-Known Member

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    The POI will be 5/16" lower than it is now.

    Ajax
     
  5. victoria K

    victoria K Member

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    We get a lot of customers that are in the same boat as you, their adjustable combs are useless to them at this point. A taller rib will at least will give you back some adjustability in point of impact. A rib with approximately a 1/16" pitch (taller up front) would also help get you to your wanted poi.

    If I can be of any help just give me a shout

    Thanks
    Vicki Keen
     
  6. victoria K

    victoria K Member

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    Here is how add on ribs can work. if you don’t raise your comb you may have the problem of the rib just up above where your looking into the back of the ramp.
     
  7. chuckles

    chuckles Member

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    Victoria, thank you very much....

    Ajax, what is 5/16" equal to at 40 yds...???
     
  8. jimrich60

    jimrich60 Member

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    Chuckles: The usual reason people use an add-on rib is to allow for a more upright head position. If they want to retain their current POI, they then also need to raise the comb the same amount/height as the added rib. In your case, since you want to lower the POI, you would still probably have to raise the comb somewhat, but not as much as the specified 5/16" rib height. As as example, on my Beretta, the book advises that raising or lowering the comb by 1/16" will change the POI by 3 inches at 40 yards. I would note this a "ballpark" figure, and that in actuality, it depends a lot on the individual as to how much the POI changes per 1/16" washer added or removed. Still, since you want to go from 60/40 to 50/50 (a 3 inch change) that would suggest that with a 5/16" rib addition, you would raise the comb 4/16" as a starting point, and then work from there (moving up or down in 1/16" increments) until your POI was where you wanted it.

    Jim R
     
  9. chuckles

    chuckles Member

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    So Jim, 1/16" will give me appx 3" at 40 yds on my pattern ...that would put me just about 50/50.

    Comb or Rib, doesn't matter... 1/16" = 3" ???
     
  10. Neil Winston

    Neil Winston Well-Known Member

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    chuckles, in this case, and assuming Jim R's advice about the comb is taken, 5/16 inch is 5/16 at one yard or 40 yards. It can change things a tiny and probably immeasurable amount (it'll shoot higher when you are all done) if you try to extrapolate to 40 yards the result you might get from 13- or 20-yard patterning, but the first part is right. You can never detect any of this in "real life," of course.

    Neil
     
  11. Ajax

    Ajax Well-Known Member

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    If everything else stays the same and all you do it put a 5/16 higher rib. All you have done is depress the POI from the original POI in the amount of 5/16", at the same distances you had measured before. If you put a rib on that taller in the front you could depress the POI as long as you are comfortable with the sight picture.

    Depending on how you see the target, you could try a larger front bead?

    Ajax
     
  12. jimrich60

    jimrich60 Member

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    Chuckles

    In theory, at least, it would not matter whether you raised the rib 1/16", lowered the comb 1/16", you would be lowering the POI by some amount. Beretta gives a figure of 3 inches per 1/16" change, but this is for my 34 inch unsingle barrel and is their estimation. I have not found that to be exactly correct for me, but I do get a noticeable increase in POI when raising the comb by 1 washer (1/16") at time. In your particular gun, the change might not be be 3 inches, but lesser or greater, depending on how you hold, shoot, etc. But it gives you a starting point. Since you have apparently bottomed out your adjustable comb and still have too high a POI for your wants, putting on a rib addition(as long as that addition is parallel to the existing rib) and then raising the comb the same height as the added rib, then gives you some more downward movement of the comb to lower the POI to where you want it. Of course, you can also have Vicki Keen make a rib to lower the POI itself, then simply put the comb at the height of the rear of rib to acheive a lower POI in another way, but just how much the change will be is both dependent on your gun and you.

    The best way I know to do this before investing a lot of money into an add on rib is to get a sheet of balsa wood with a thickness about the width of your rib. Then cut a strip at the height you think you would like to add a rib (say
    1/4 or 5/16" and as long as the existing rib. Paint it black, and attach to your rib with some electrical or similar tape. If you want beads, cut a round head pin short and stick it into the balsa. Then try it out, putting the comb up the distance the added balsa rib is high. Move the comb up or down to achieve the POI you want. Once you have determined whether you like the solution, and know what rib height you would like, then you can order a rib from one of makers such as Vicki Keen or some one else. (Vicki Keen is great to work with and can pretty much work up just about anything you need at reasonable prices).

    Ajax also made a good point. As long as the desired change in POI (lower) is small, you might be able to get close simply by using a larger/taller front bead. In this sense, the front bead acts as a rifle/pistol front sight and so by raising the front sight/bead, you lower the point of impact.

    You have to remember that in a shotgun, the rear sight is your eye and front sight is the bead. That is is relationship that counts. To lower the POI, you can either lower the rear sight (your eye), or raise the front sight (bead). For those who say that you should not see the front bead in shotgunning, they are correct but only on a conscious or bead checking basis. You should and must be focusing on the target, not on the bead, barrel, etc when shotgunning. But the subconscious is using that front bead as a reference point all the while, so it does play a role in properly pointing the shotgun in the right place. If this were not so, and there was absolutely no subconcious reference point, you would simply not be able to properly point the shotgun in reference to the moving target. The eye/bead/target alignment does indeed occur, it simply is done by the subconcious.

    Jim R
     
  13. chuckles

    chuckles Member

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    Thanks for all the good info folks...
     
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