Moderator POI

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    AnimalHitman
    Participant
    Member

    Does an after-market moderator affect POI? In other words, will I have to re-chrony, zero, and range my Wildcat .25 MKI after installing a DonnyFL SUMO moderator? Thanks 🙂

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    donnyfl
    Dealer
    Dealer

    Any disruption to the airflow of the pellet will most likely change the POI and you will need to re-zero. A way around this is by getting a moderator a size up. This will happen with adding a muzzle break/air stripper/moderator.

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    addertooth
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    My POI changed on one air rifle, but I learned the alignment on the moderator was not perfect, and the pellet was clipping the baffles.  I fixed the alignment, and the POI returned to normal.  On my other air rifle, I was super careful on the alignment when I installed a Moderator (lessons learned), and it's POI did not change one bit.  

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    Eaglebeak
    Participant
    Member

    Adding anything to the end of your barrel will affect your POI. I have a Walther MaximaThor that has a barrel weight on the end of its' 24- inch barrel. Removing it will move the POI over 1 inch diagonally at 25 yards. Adding a moderator to it or my other rifles has the same effect + or – 1/2 an inch. It's about harmonics. The accuracy is not affected, just the POI.

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    airgunfans
    Participant
    Member

    Agree that the change in POI is more due to the adding of weight to the end of the barrel. my Alecto pistol has the POI shifting up if no moderator is added. That's because the muzzle jumps up more during firing without the weight of the moderator. The grouping is totally unaffected

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    AnimalHitman
    Participant
    Member

    Wow, a reply from the Master himself! I realize now that the point is moot, because I need to throw some lead across a Chrony anyway because it's got to the point where I've shot enough pellets to where the hammer has seasoned. (I bought my WC new.) Now is a perfect time to re-Chrony. At any rate, thanks for the uber-responses, guys!

    Another esoteric question: Will POI change as the felt inside the moderator degrades?

     

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    broekzwans
    Participant
    Member

    The POI change has barely anything to do with harmonics or disruption of airflow (except when it’s clipping). The added weight causes the barrel to bend more and therefore is the biggest influence on the POI shift, this means the POI will move down. The better the barrel is supported (by a barrel band for example) the less the POI shift will be noticeable, a barrel band has other drawbacks but that’s not the question here. Attaching a lighter moderator will also decrease the vertical POI shift compared to a heavier moderator.

     

    You’ll only need to re-zero the gun, the rest stays the same if the moderator is attached properly.

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    AnimalHitman
    Participant
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    Thanks for that, bro' :-). Ya never stop larnin'. (Except when ya get to Heaven)

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    Eaglebeak
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    broekzwans

    The POI change has barely anything to do with harmonics or disruption of airflow (except when it’s clipping). The added weight causes the barrel to bend more and therefore is the biggest influence on the POI shift, this means the POI will move down. The better the barrel is supported (by a barrel band for example) the less the POI shift will be noticeable, a barrel band has other drawbacks but that’s not the question here. Attaching a lighter moderator will also decrease the vertical POI shift compared to a heavier moderator.

     

    You’ll only need to re-zero the gun, there rest stays the same if the moderator is attached properly.

    Surely, you jest?

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    broekzwans
    Participant
    Member

    Eaglebeak

    Surely, you jest?

    nope not joking, I've done my research and testing. A barrel is curved when it's installed in a gun, you can decrease this by truing in a lathe but all non-custom manufacturers don't do this.

    If the barrel is pointing in the 12 o'clock position the amount of weight determines how far it bends towards the 6 o'clock position.

    If the barrel is pointing to a let's say 2 o'clock position, it will also start to move towards the 6 o'clock position but with a curve coming from 2 o'clock. So yes, there is indeed a vertical and horizontal displacement posible but it will always go towards the 6 o'clock position but the amount of POI change is dependent on the amount of weight attached and the stiffness of the barrel.

    You can try this yourself, get some different moderators with different weights and some slabs of lead as extra weight. If you have the possibility of rotating the barrel add that to the mix and find its resting direction on the clock. Keep in mind, this effect is more visible in free-floating barrels. Barrels that are locked in place by a barrelband will barely show any POI change.

     

    So, only need for re-zeroing, no need to re-range or re-chrono. Since the barrel of the wildcat is supported up to half way the POI shift will probably be quite small.

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    Eaglebeak
    Participant
    Member

    I'm sorry, but I can only pass on my own findings. I have two PCPs both with barrel bands and a rimfire with a 3/4 length wooden stock. They all exhibit a point of impact shift diagonally of between 1-1.5 inches at 25 yards when adding a small unbaffled moderator. I just can't believe that a steel barrel will flex, even .0001 of an inch with the weight of a 4 1/2 ounce moderator on the end especially if it has a barrel band for support. I used to believe that the shift was caused by turbulence but if that was the case, it would be causing fliers not a shift with no loss of accuracy, in fact, in my experience, accuracy is slightly better with the moderator attached. After watching a Mat Dubber video on the subject, it all made sense.

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    AnimalHitman
    Participant
    Member

    I agree. The Samurai of Silence himself, DonnyFL, says that the disruption of airflow of a moderator will shift POI and requires a re-zero. Running a new shotstring is also in order, IMO, if you are using ballistics software..

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    kueblerja
    Participant
    Member

    I have built three moderators and every one of them has changed the POI just a little bit.  The main thing is to make sure that the pellet hole opening is zeroed from the pellet bolt end to the end of the moderator.  Sometimes it will actually increase the velocity of the pellet.

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    AnimalHitman
    Participant
    Member

    kuebleja:

    Your post raises an intriguing issue. I got some interesting results when I ran a shot string with my DonnyFL SUMO moderator. Whereas the two prior shot strings I ran on my Wildcat sans SUMO were basically consistent in the fps, the shot string I ran with the SUMO had a relatively large variation in fps. The average fps in all three shot strings, however, were very close to each other.

    I am going out later today to zero and range with my new SUMO installed to validate my Chairgun numbers. So, hopefully my WC still shoots true. Up to now, my Chrony and Chairgun numbers have been true-blue.

    Here are the three shot strings I've run on my Wildcat. I bought her new from AOA in September 2017, and ran my first shot string right out of the box:

     

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