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***ADJUSTING POI***

Discussion in 'Shooting Related Threads' started by threedeuces, Nov 2, 2009.

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  1. threedeuces

    threedeuces TS Member

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    Can I adjust my POI by only adjusting my rib or do I have to adjust my comb the same distance as I did the rib. My owners manual says I have to raise the comb the same amount as lowering the rib to raise the POI.Just wondering, they kind of have me confused now. All I ever done was adjust the rib.
     
  2. V10

    V10 Well-Known Member

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    Yes
     
  3. luvtrapguns

    luvtrapguns Well-Known Member

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    If you raise or lower the rib you should also raise or lower the comb accordinly to maintain the same sight picture. By that I mean keep the sight beads stacked the same after making adjustment(s). Hope this helps, Marc
     
  4. phirel

    phirel TS Member

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    To me, the sight picture in not relevant to anything. Your POI should go up if you either raise the comb or lower the front sight. I can also make my gun shoot higher if I go after the bird with more aggression, hold a little lower gun and swing the gun faster.

    Pat Ireland
     
  5. 635 G

    635 G Well-Known Member

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    Pat-do you think the heavier the gun, the lower hold point? I mean if a gun is heavy it takes more time to gain momentum. If I try a higher hold, I seem to be shooting behind some targets.

    Phil Berkowitz
     
  6. phirel

    phirel TS Member

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    Phil- It does take more force to move a heaver gun, but once it begins to move, it requires more force to stop it. You mentioned shooting behind targets with a high hold. This suggests that you don't see the target leaving the house when holding high.

    For me (I am a one eyes shooter), I seem to shoot targets faster by holding a lower gun. I hold lower for handicap targets than I do for singles and doubles and I shoot the handicap targets faster.

    Pat Ireland
     
  7. jimrich60

    jimrich60 Member

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    The POI is determined by the line of sight between the rear sight (your eye in the case of a shotgun) and the front sight (bead). What this means is that you can/will raise the POI by either raising the comb, or lowering the front bead/rib. If you do both, you raise the POI by the combination. If on the other hand, you raise the comb, then raise the front bead/rib, you are in effect cancelling out some or all of raise in POI you got by raising the comb in the first place. The middle bead is (or should be) completely irrelevant to setting the POI. It is natural when raising the comb, that you will "see" more the rib top, and the relationship of the middle bead to the front bead will change. But the middle bead really should only serve to align the gun (i.e., cast on/cast off) and to ensure that the gun is not canted when shouldering it. Otherwise, it really should be ignored as it plays no role in setting POI. Many will advise first using the comb to achieve proper POI, then "changing the rib" to reachieve some mythical required figure 8 with the middle and front bead. This is not only unnecessary, but counterproductive, since changing the will further affect POI, either further raising it (if bead if lowered) or lowering it (if bead is raised) A few shotguns are made with the rib hinged at the front so the back of the rib can be raised or lowered without changing the front bead height and with these you could change to "see that figure eight without changing the front bead but they are few and far between. So just set the comb to proper height for the POI desired, if needed you can then use the rib to "fine tune the POI" if needed (since rib ajustments are in much smaller increments than comb usually) and then leave it alone.

    Jim R
     
  8. zzt

    zzt Well-Known Member

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    three dueces, yes. Let me paraphrase the instructions that came with my Perazzi (adjustable rib and comb). If you want to have the same view down the rib after the adjustment, you must add or subtract (depending on which way you move the rib) 2mm of spacers under the comb for each notch moved.

    The manual states that lowering the rib 1 notch in front and raising the comb by 2mm will move your POI up by about 4" @ 40 yards. Your bead alignment will stay the same.

    In reality, these are independent adjustments. Lowering my rib 1 notch and leaving the comb unchanged raises my POI by 1.4" @ 40 yards. Leaving the rib alone and raising my comb 2mm raises my POI by 2.6" @ 40 yards. These changes are additive. So lowering the front of the rib 1 notch AND raising the comb 2mm raises POI by 1.4" for the rib adjustment AND 2.6" for the comb adjustment, for a total of 4" higher @ 40 yards.

    The bottom line is your preference for sight picture. If you really want to see the same bead alignment all the time, regardless of POI, then you will move both together. This will limit you to 4" increments (on my gun).

    If you don't care about seeing the same bead alignment, you can adjust each independently. You'll have more fine tuning available, because you can adjust your POI by 1.4", 2.6" or 4" increments.
     
  9. houbyhunter

    houbyhunter TS Member

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    Interesting, my Perazzi MX10RS rib manual (USA) directs me to move the comb 1/8" for every notch on the rib. In addition, it moves the POI 3 1/8", 6 1/4", etc. In my case, the comb shims are in metric, so a 3mm spacer would be the closest to 1/8". No where in the manual does it state the distance for the POI change. Understandable that plus or minus an inch at 40 yarads is not much.

    Randy Kalal
     
  10. zzt

    zzt Well-Known Member

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    Randy, I just went down and looked at a newer manual marked for all USA models with adjustable ribs. All the dimensions are in US Customary Units, not metric. It states that moving the rib on any US model one notch and adding or subtracting 1/8" of comb spacers moves POI by 3 1/8". I wonder what barrel length they calculated that on.

    In any event, the basic scenario is the same. You can move one, the other, or both to fine tune your POI changes.
     
  11. luvtrapguns

    luvtrapguns Well-Known Member

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    zzt,
    Thank you for, in my opinion, an excellent explanation of how comb and rib adjustments influence each other regarding POI. My simplified version tried to answer without getting all techy. Keep the sight picture the same after adjustments of rib and comb and it it one more variable you do not have to compensate for.

    Raising just the comb will raise POI, no doubt. But in doing that you change the view down the rib and have to learn a new site picture, one that may have taken considerable time to develope. By adjusting comb and rib in combination you can raise or lower POI without changing your site picture. After all, why have both adjustments if they do not have reason? (marketing hype is not an acceptable answer)

    There have been several opinions expressed on this site. Not all agree. I wonder if it is because some have not stopped to analyze the entire comb, rib, site picture scenario. Your manual seems to explain it pretty well. I would think the manufacturer has it figured out better than most. Try the one, or more, technics that make the most sense to you.

    Good shooting,
    Marc
     
  12. threedeuces

    threedeuces TS Member

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    Thanks guys for the explanations. I think I have it figured out. Sometimes it is hard trying to put it all together.
     
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