Moderator or Shroud?

Forums General Discussion Moderator or Shroud?

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    oldsparky
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    What I am wondering is, If you have a Moderator that adds 6” to the barrel length . And a Shroud that adds 6” to the barrel length will the DB reduction be similar? Oh and a comparative diameter of both. On the same gun.

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    mmahoney
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    If the shroud has baffles in it like the moderator does, then yes, the db reduction will be similar.

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    davecole
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    I bought both a shroud and a threaded moderator for my taipan.22. 

    The shroud added virtually zero length whereas the moderator added about six inches.

    Db didn’t change only the tone of the firing cycle.

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    bucketboy
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     A well made shroud of the same Dia and the same projected length past the end of the barrel  should easily out perform a similar moderator. The reason being the air is able to expand in the space between the shroud and barrel, this slows the air as it finally exits the endcap.

    i made this for my grandson, 35mm Dia, 500mm long (125mm past the end of the barrel). Genuinely, the noise from the pellet tearing through a paper target at 30 yards is louder than the muzzle report. This is by far the quietest airgun I have every heard.

     

    Another advantage of the shroud is it adds stiffness to the barrel, this can aid accuracy, the disadvantage are, you will need higher scope mounts for clearance and being fatter for longer, a shroud is more difficult to keep under control in the wind.

    Bb

    • This reply was modified 5 months ago by bucketboy.
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    intenseaty22
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    A word of caution though. My Cricket Mini came with a stock shroud on it’s floating barrel. Problem was, it put tension on the barrel as it screwed on and actually pressed against the breech. This caused some shifting in POI with temp changes. 

    This change in POI stopped after I switched to a moderator and a false shroud. 

    I would think the sound moderation would be about the same or better with a shroud of same length. I would just not let it tension the barrel. 

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    STO
    Participant
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    So, in essence, what Bucketboy said: all else being equal, a shroud will SUBSTANTIALLY outperform a moderator of equal internal architecture, post-muzzle-length, and diameter. I say this, not as a guess, but because I've actually performed a substantial number of experiments and documented a handful of them in this thread:

    https://www.airgunnation.com/topic/fx-crown-bespoke-moderator-tesla-gas-diode

    So if you're curious, it is a great read and the answer to your question is actually buried in there. I would, however like to pour a little data directly on this fire for those not interested in wading through 7 pages of long posts. I'm going to simplify things a little and skim over some details for the sake of brevity, but this should give you a reasonable idea: 

     

    Here is a moderator on an unshrouded .22 caliber airgun:

     

    And here is the same mod on a shrouded .22 caliber airgun:

     

    As you can see, there is a SUBSTANTIAL improvement in sound attenuation, notable not just in the lower peak but in the post peak sound. (again there were a few simplifications in here) 

    The reason for this is reflex volume, That air, after it is initially deflected/delayed, wants to go in all directions, so this gives it a direction to go in other than forward out the muzzle. That allows the moderator to experience lower pressures, and thus makes it quieter. I should add that, if you're in the stage where you're designing and building mods, not just buying them, this allows you to focus more of that precious space toward sound damping and less on flow delaying. This is why, when asked, I recommend dramatically different moderator configurations for mods on shrouds vs. direct muzzle thread. No two ways about it, it is a lot harder to muzzle that bark if you only have the moderator's volume to contain it. 

    Speaking of damping sound, it is also worth noting that sound loves to reflect and run up and down hollow tubes. Putting some sort of damper in your shroud can also measurably improve your sound attenuation. I actually posted an entire thread to this effect, which if you're curious might also be worth a quick skim:
    https://www.airgunnation.com/topic/shroud-damper/

     

     

    As far as the question of shroud or mod goes though, I'd argue it is a false dichotomy. As mentioned above, for scope clearance reasons and for internal architecture reasons, relatively modest diameter shrouds are best. But when you get to the mod itself, the best overall performance generally comes from designs of slightly larger diameter than you'd want your shroud. (again, ref. my big test of all the major designs on the market HERE.) So the optimal solution, in my opinion, would be a shroud at the back, with a damper, and then a moderator at the front. The FX shroud design is quite a good one, in my opinion, where it is retained NOT by the gun's muzzle, so differential heating shouldn't affect POI. It also is silly easy to service. 

    Just my 2c. I hope it was helpful/informative. :) 

     

     

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    oldsparky
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    thanks for the reply. I thought the shroud would be quieter. This is good reading

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    bucketboy
    Participant
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    Here is another of my shrouds, 30mm Dia, 500mm long

    also ridiculously quiet

    A few more

    Bb 

    • This reply was modified 5 months ago by bucketboy.
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    Diamondback
    Participant
    Member

    You can’t compare length and effectiveness, design is the key to effectiveness.

    My BSA R10 MK2’s came with full length shrouds that made them quite long. 

    The shrouds have 1/2×20 threads so I added an HW ldc. Rig was quieter but too long.

    I removed the shroud and found the barrel threaded, so I installed the HW ldc straight onto the barrel. Ended up shorter and quieter than with just the shroud, or with the shroud & ldc.

    I had an ldc that was large & heavy, well made with inserts and material in it. Don’t know who made it, but barely reduced noise.

    Then I tried a Decimeater and the difference was surprising. Decimeater worked great and was a touch smaller and a good bit lighter.

    Design is the key.

     

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