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Moving point of aim left or right

Discussion in 'Uncategorized Threads' started by SWIFT, Apr 29, 2008.

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  1. SWIFT

    SWIFT TS Member

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    Using the front and middle bead as sight and patterning my gun at 13 yards the POA is off 2" to the left. I know I can adjust the height by rasing or lowering the comb but to get it to move L or R this has to be a function of the barrel strightness, or in other ward a bent barrel would cause this. Am I correct??? Thks for any advise.
     
  2. jimrich60

    jimrich60 Member

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    Swift

    No, the cause for the POI being left or right (POA is point of aim, POI is point of actual impact) is caused by the sighting plane (i.e., your line of sight) being slightly off to the left or right. For most people, this is a matter of body and facial structure and how you fit to the gunstock and comb thickness. To move the POI to the right you need to move the rear sight (your eye in the case of shotgun) to the right. With an adjustable comb, you can shift the comb a little to the right (1/16-1/8 inch) to move the POI to the right. You may need to experiment a bit. In guns without an adjustable comb, this movement could be done by "bending" the stock (has to done by an expert) or in some semi-autos like the Beretta, using the supplied shims. This is referred to as adding "cast-off."

    Jim R
     
  3. phirel

    phirel TS Member

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    If the mid and front beads are aligned and you accurately aim the shotgun at a 13 yard target, and it consistently shoots to the left, the problem is in the barrel.

    Make sure you shoot several tests to make certain that you did not pull off of the aiming point. If I shoot 10 tests at 13 yards, it is not unusual for 2 of the shots to be off.

    Pat Ireland
     
  4. mercedesman1981

    mercedesman1981 TS Member

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    Pat,

    If you shoot 10 targets at 13yds, do you see poi's about equally dispersed
    between left and right (perhaps up and down too?)

    Thanks,

    Mike
     
  5. Kolarmaxx

    Kolarmaxx TS Member

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    Funny to read this. I just went through this myself. I start missing hard rights I used to hit. Pattern the gun and I'm shooting 2-3 left of center. Pattern standing and on the bag, same results. Move the comb right and not much help. Show the dealer and says yes, gun is shooting left. Send it back to the manufacturer with the idea the barrel somehow bent and voila, rib is bent. Misaligned from day one the service guys tell me. Nice to know it wasn't in my head like everyone at the club accused me of. Had Kolar put on the new high rib while it was there and Mark did an awesome job. Funny how you can smoke them once the guns shoots where you point it. Chris Gallagher
     
  6. maclellan1911

    maclellan1911 TS Member

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    I had the bench riffle shooters at our club sight my gun in buy the sights, barrels checked out ok, although they laughed at me couse I wanted to know where a scattergun shoots they where very helpful in ruleing out a "bent" barrel. After I went through Neil W method and help from Pat I and a host of others and have my gun shooting where Im looking/pointing. The beads no longer line up or stack
     
  7. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    Ribs can be installed off center to the bore line as mentioned above. I call these "Monday" guns. I've had a couple of those Monday specials, had Simmons fix one, sold the other. Hap
     
  8. phirel

    phirel TS Member

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    Mike- When I shoot 10 targets at 13 yards from a rest I find that 8-9 are centered in the same place and 1-2 are off. The stray shots are due to my pointing error.

    Pat Ireland
     
  9. miketmx

    miketmx Well-Known Member

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    Do you know how to bore sight and a read a Barrel. Insert a deprimed 12 ga empty hull in the breech and a deprimed 20 ga empty hull in the muzzle and look through the breech end at a light source. If the barrel shows perfectly concentric rings then your barrel is "true" ie. not bent. Put the deprimed 12 ga empties in both chambers and rest the barrel set on a picnic table in your back yard and look through the bore at a distant bullseye on the back fence then raise your head without moving the barrel set and note the sight picture down the rib at your target. This trick will give you some valuable information without actually shooting the gun. Let us know the results.
     
  10. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    miketmx, that's very good information to share. Using both those deprimed hulls as peep sights, will give you information on how "shot drop" works as well. Hap
     
  11. CharlesR1100

    CharlesR1100 TS Member

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    Miketmx and Hap...use the peep sight process with caution, as in all things ballistic. I have a K 80 TS over and under which shoots both barrels to the same POI. Which is fine. It is what I want. Great.

    But when using the peep sight process described, it shows the under barrel POI "shooting" very flat and the over barrel POI "shooting" high. (The adjustable sight is set for 70% high.) I do not think the under barrel is bent up, but it may be. One conclusion: the peep sight will not predict POI with a slight barrel bend up or down. Nor perhaps right or left.

    But, if neither barrel is bent, and if both barrels do actually shoot to the same POI, but show different POI via peep, the peep sight process does not work.

    Plato is reputed to have said, "Do not argue about how many teeth should be in a horse's head. Count them."
     
  12. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    CharlesR1100, what Mike says works for true straight tubes, not bent. It shows concentric rings which means the barrel straight.

    "One conclusion: the peep sight will not predict POI with a slight barrel bend up or down. Nor perhaps right or left."

    This "peep sight" method won't tell you the POI at all. It just aligns the bore in a true straight line to a mark on the paper at 40 yards. Your POI pattern center will be approx. 4 inches below that mark. Neither Mike or me said anything about this method being used to determine a POI? Hap
     
  13. miketmx

    miketmx Well-Known Member

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    Okay, I agree the "Bore Sighting" trick does not accurately show POI but it gives a relative approximation of POI in the privacy of your own back yard without actually shooting the gun at a pattern board. I think this would show if the rib was not on straight and the "reading the rings" thing would tell if the barrel was bent. In my own case my MX-3 is designed to shoot Top barrel first and the Top barrel does in fact shoot a tad bit higher but the bore sighting at home showed the Bottom barrel with a little bit higher POI.
     
  14. CharlesR1100

    CharlesR1100 TS Member

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    Hap...of course you are correct about shot drop not reflected in the peep sight. So what? That is not the point of using the peep sight. At least for me. Perhaps for you it is.

    To what end would you or anyone discuss here the use of a peep sight unless it was in connection with both POI and POA?

    Finally, what Mike "says" kmost certainly is for all barrels, both bent and straight. In fact its only purpose is to determine if the barrel is bent!
     
  15. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    CharlesR1100, I use those deprimed hulls as one would peep sights to determine if my barrel is true and straight. Then, with the gun locked in a gun vice with those hulls inserted in the chamber and barrel end, I know where the bore center is pointed at 40 yards. Then I look at the rib and bead to see where it relates for a comparison between the two marks on the paper at 40 yards. After doing this a lot of times, I've learned I can come really close to telling where that gun will pattern, with a straight barrel. With a cut-off 20 ga. hull, you can tell if the choke has been monkeyed with by the rings if the choke is polished. So, that's how I used the term "peep sights" in what I wrote above. BTW, I also use real peep sights on a couple of my rifles. Hap
     
  16. mercedesman1981

    mercedesman1981 TS Member

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    Power stuff here.

    Awhile back I discovered my POI to be about 4" to the left at 38yds and had a tough time trying to figure out why because my POI testing at 13yds indicated otherwise. Neil Winston and ZZT were quite helpful and I heartily thank them both.

    Using the bore sighting technique above, instead of removing the 20ga shell from the muzzle, I left it in as I could easily pick up a target through it. I can clearly see how off center my middle bead is which is what I was using for pattern testing / POI testing at 38yds. With the bore sighting technique, the mid bead is to the right of the front bead when looking from the rear. When measured on the rib, the bead is not centered.

    Is there anyone in the Seattle area that knows where I could take this gun to have this problem fixed, or am I going to have to send this out for a quality repair?

    I can only guess the rib is on straight, but I want to have that checked too.

    The gun is a Browning XT, bought new last year.

    Mike
     
  17. CharlesR1100

    CharlesR1100 TS Member

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    Hap...yes, I use the peep sight for the same reason.

    You can improve the meathod by removing only the anvil part of the primer in both hulls. That will reduce the size of the peep on both the 12 and 20 ga hulls.

    Another improvement is to rotate the 20 ga shell opening to 3, 6, 9 and 12 o'clock, keeping the choke fixed, noting the difference, if any, in the poi.

    Further, if the choke is a tube, rotate (unscrew) it (again 3, 6, 9 and 12 o'clock) with the 20 ga fixed in the choke tube to see if the tube is straight.
     
  18. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    CharlesR1100, thanks for the heads up. I've never tried that with choke tubed guns. Good idea. Hap
     
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