How does a moderator affect velocity

Forums General Discussion How does a moderator affect velocity

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    danhor7
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    So I’m experimenting with this a bit and wonder what you guys have experienced along these lines.

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    peterdulux
    Participant
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    Looks like your fps were creeping up anyways. Is that regulated?

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    KYAirgunner
    Participant
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    I don’t know that guns extreme spread should be around 10 fps. I think that you would have to keep taking it off shoot it and put it back on and shoot it several times to come to a conclusion.

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    gorgata
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    that’s a wild cat and its regulated but it seemed like the fps was creeping up anyways id like to see 2 separate 10 shot strings to make a good conclusion

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    Wellgun
    Participant
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    i also experience this with my .22lr, and even my .308 so that’s not really new, when you put a supressor/silencer/moderator (since i dont know how to call this ^^ ) there is a small increase of the bullet velocity… not a lot, and its even less with bigger calibers, but you hvae to take this in concideration if you’re shooting with and without it without re-zeroing your scope ;) 

    when i was searching for similar experiences, i’ve seen this video, which is pretty intresting… of course its firearms, but the effect of the supressor is the same than on an air rifle ;) 

    Edit : Woops, i didnt saw that you got LOWER velocities with the supressor… well i cant help you this time ^^

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    danhor7
    Participant
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    Peter,
    Yes it’s regulated.  Holds pretty steady down to about 100 bar and then drops off very noticeably.

    KYAirgunner,
    Yeah I agree I need more data points.  I haven’t had the chronograph very long and usually don’t shoot through it when I’m just plinking.  Guess I should start there.

    gorgata,
    I hadn’t really considered the whole string but that’s a really good point.

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    Ginuwine1969
    Participant
    Member

    You don’t even have to do a whole string, fill it up shoot 10 – 20 shots with the moderator off, fill it back up again and do it again with the moderator on.  That way you are comparing apples to apples.  As far as the creeping up, in my opinion it wasn’t you ES looked pretty good comparing each group individual.  Should not compare each groups ES to each other.  A moderator strips air from the back of a pellet before it leaves the end of the muzzle, so i would make since that the pellet slows down a little bit.  That is my 2 cents.
     

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    NeilClague
    Spectator
    Spectator

    There is no evidence of a moderator slowing down pellets, I have heard back from several customers and a well known maker of big bores who have tested their guns with my moderators on them and have seen an increase in velocity. Not much but 15fps on a big bore is a welcome increase. I am not sure why you think the moderator would slow them down, it is holding the energy behind the pellet longer, just as a longer barrel would and you know a longer barrel increases velocity. I have also noticed a slight increase in velocity, it is only small but it still indicates that a moderator does not adversely effect the velocity of pellets, Neil.

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    clgraham82
    Participant
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    BTW…if that’s the one you built…looks good on the WC!

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    danhor7
    Participant
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    Neil,
    That’s a solid logical theory.  I need to do a lot more shooting to rule out any variables that may have thrown off my initial testing.  I’m all over it. 😉

    clgraham82,
    Yes and thanks.  I think I’ll change up the inlet plug to have an external chamfer that makes a nicer looking transition from the diameter of the FX barrel out to the Carbon Fiber tube diameter.
     

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    bill_dd97
    Participant
    Member

    Neil is correct. I’ve seen several videos (mostly PB guns) that show a moderator, or whatever, causing a slight increase in velocity. I have also done some shroud testing with my Marauder that gave the same results. Basically a moderator adds some virtual barrel length which aids an increase in velocity.

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    danhor7
    Participant
    Member

    Well here’s my results after recording 50 shots 25 moderated and 25 naked.

    I was using Crossman Premier Domes which are 14.3 grain

    Using the moderator the 25 shot averaged out at 966.4 including one anomaly that was well below the average at 954 and a high of 973

    Without the moderator the 25 shot average was 960.96 with a low of 956 and a high of 967

    Indeed the projectile seems to continue accelerating while inside the moderator which makes sense with Neil’s reasoning.  I thought that perhaps it would be like a bullet train entering a tunnel where suddenly the train is displacing air confined to the tube.  

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    clgraham82
    Participant
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    Good info!  Can we see a close up of the moderator (LDC) on the wildcat?

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    danhor7
    Participant
    Member

    Sure. Here’s my thread about the build.
    http://airgunnation.dev/topic/home-made-moderator/

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    danhor7
    Participant
    Member

    Looks like Photobucket is acting up at the moment, but here it is.  The prototype anyhow.
    Here’s a 360 of the silencer.

    And a picture of it on the gun from another web picture hosting source.

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    clgraham82
    Participant
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    Good job…looks great!

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    Zephyr
    Participant
    Member

    Have you seen the effect on POI of this change in fps? 

    I have noticed the POI changes vertically and horizontally when I fit a moderator, but.. the ES and grouping was improved. While it’s nice to have a low ES number, I’d rather have tight groups that I can zero on target.

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    danhor7
    Participant
    Member

    Thanks clgraham! Im pretty happy with the looks myself but intended to further improve in the looks department moving forward.

    Zephyr,
    Well as a percentage, it’s only 0.625% increase in velocity, so almost nothing. The bigger concern I have is that a force is being applied to the projectile while in freeflight. Much like a tail wind that exceeds the pellet velocity. Then as it passes through the exit tunnel, the pressure waive could side load the pellet if it isn’t perfectly concentric. I just dropped a 0.22 diameter rod into the barrel and found that indeed I had a slight axial misalignment which I’ve corrected and I’m getting ready to do some shooting but the wind is gusting, so not going to learn much. Just trigger time fun for now 😉

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