Shroud+moderator interactions

[weevil]

My Panthera has me wondering about the effects of interaction between integral shrouds and external moderators. My 600s are shockingly loud with no external mod and then unexpectedly quiet with just a small external mod like a Huma 30. To be clear, or at least as I understand it, the Panthera shroud is just an open chamber behind the muzzle, with a stripper but no forward baffles. My sense is that the shrouds do little alone but that there is a synergistic interaction when both are used. In other words (Aristotle’s): “the whole is greater than the sum of the parts”.

We engage in endless debate here regarding moderators and my sense is that there are no universal winners but rather it’s a matter of “horses for courses”. However, I don’t see any discussion of interactions and wonder if any experts here, such as @subscriber or @OldSpook, have insight. At a basic level, I’m wondering if external moderators can enhance the utility of a shroud (or vice versa) and if so, are there moderator designs/features that are favorable for use with shrouds? If so, we can establish that certain horses are better for shrouded courses, if you get my drift. Thanks in advance for any contributions!

 

[subscriber]

weevil,

Your contention / speculation about mufflers enhancing shroud performance, and vice versa are correct. Some moderators are better at muffling than others when attached to the bare muzzle. Others moderators perform better when boosting a shrouded PCP. As such, the moderator that "wins" when attached to a bare muzzle may not be the same one that wins, when attached to a shrouded PCP.

So, as you say the system is more than the sum of its parts. Probably has to do with relative natural frequencies and impedance matching.

Certainly, for a basic shroud, adding a muffler turns the shroud into a large primary blast chamber. Here is some test data on the subject:

20 Silencer Test - Airguns & Guns Forum

20 Silencer Test, Air guns, Airgun Forum

www.gatewaytoairguns.org

Fourteen (14) LDC Test - Airguns & Guns Forum

Fourteen (14) LDC Test, Air guns, Airgun Forum

www.gatewaytoairguns.org

 

[Long_Gun_Dallas]

Most shrouds have a large exit. So, air and pressure easily escapes. Not sure if this is the case with the panthera, but was with my Crown. In a scenario like this, additional baffles forward of this would create backpressure and theoretically cause more pressure expansion in the shroud than prior. Many variables come into play. Fluid dynamics, frequency dynamics. Generally, the best performing baffles I've seen create the most turbulence, while also maintaining a very small bore size.

I guess your scenario does sound a lot like the old crown barrels with the extending shrouds. Internal air stripper, then can be extended to open up a blast chamber. I have one of these in 600mm/30 cal. Collapsed, quite loud. Extended, quiet enough I have never installed a moderator or even a moderator adaptor on it.

 

[weevil]

That was my “unprofessional” interpretation too LGD. Thanks!

Here is my interesting observation: The Huben GK1 pistol is an absolute firecracker, lacking a functional shroud and producing massive power from a 9in barrel. Even with some pretty large conventional mods such as Donnys and Humas, it remains pretty loud. Yet when I put a much smaller impulse air on it, it quietens right down. However (and all of this is subjective; based only on my ears, but nonetheless not subtle!), a Tatsu or Huma30 does much better than an impulse air on my Pantheras. So, I’m wondering if there are things to be learned regarding the differences in design.

@subscriber: Thanks for your valuable input. I had seen those threads before but had not evaluated them in the context of this question. I appreciate the design and approach used in those test but am dismayed by the fact that they use so many offbeat and proprietary designs, such that only a small handful of the test subjects are available to the average Joe. It’s akin to having a car magazine run an article comparing cars that have various undisclosed engine mods. In any case, it does at least show that the interaction element is real. I totally understand if you would prefer not to divulge your hard-earned IP regarding design features on this public forum.

 

[Long_Gun_Dallas]

Could be due to the baffles interaction with different levels of pressure or volume. Air behaves like a fluid, and behavior with shift with varying levels of volume or pressure. So, it stands to reason some baffle types (and expansion chamber sizes) will respond more to a certain range of variables where another may not. One thing I have noticed is my mod30s tend to respond positively to having a short expansion chamber either in the middle of the stack or just before the last one. I also like removing felt from all chambers but the last.

 

[denovich]

I think the shroud provides a large volume for the initial blast to expand into, this helps separate the pellet from the charge of air.... which helps keep all that air from just following the pellet out through the baffles. That in turn keeps the pressure in subsequent chambers lower allowing for further expansion/disruption/dampening before it makes it out the end.