Question about exposing pinhole on shroud?

[Goldwing]

Question about exposing pinhole on shroud, what's the effect of covering it with a CF tube?

Should it be maintained for air escape or minimal in importance?

Thanks

Dan

 

[PeeWeeDaddy]

A couple of years ago I had a PRod tuned by a person in Sacramento who shall go nameless.

He drilled a small hole at the extreme rear of the shroud I suppose to allow trapped air to escape.

What ever benefit is expected from the hole will be negated by covering it.

If it was me, I would drill through the CF into that same hole..

 

[pnwairgunner]

Some people believe a vented shroud is quieter, but every one I’ve seen has been louder and benefits having a wrap of black tape around the shroud to seal the vent.

Try wrapping it with tape and see! If it adversely affects it you can easily remove the wrap of black tape.
You could also use a wrap of foam around the barrel Inside the shroud ahead of the vent hole to slow the escape of air from the vent, making it quieter.

 

[Goldwing]

Is the hole strictly a dB sound reducer or is it there to relive pressure build up?

Somehow I think its to relive pressure saftly

Thanks

 

[pnwairgunner]

There is no pressure build up in any shroud. It is not a sealed vessel.
The purpose of shrouding a barrel is to moderate shooting sound levels, not air pressures. 

 

[Feinwerk]

There is most certainly a momentary pressure pulse inside a shroud at the time a shot is fired, from the time the pellet exits the barrel inside the shroud and then begins passing through baffles, if any, and then exits the shroud. Pinholes in the rear end of the shroud will begin to vent this air and can reduce the volume of air expelled behind the pellet. I have experimented with this in my Marauder rifles. If the pinhole faces the side where your head is, you may hear more noise during the shot depending on how large the hole is. If the pinhole/vent hole is placed on the side opposite of your cheek rest, then it is less noticeable and there is most certainly less air exiting the muzzle helping to reduce the report in that direction.

You can see for yourself by holding a lighter, candle flame, or piece of tissue next to the pinhole and firing a shot to see the deflection.

Regards,

Feinwerk

 

[Goldwing]

There is most certainly a momentary pressure pulse inside a shroud at the time a shot is fired, from the time the pellet exits the barrel inside the shroud and then begins passing through baffles, if any, and then exits the shroud. Pinholes in the rear end of the shroud will begin to vent this air and can reduce the volume of air expelled behind the pellet. I have experimented with this in my Marauder rifles. If the pinhole faces the side where your head is, you may hear more noise during the shot depending on how large the hole is. If the pinhole/finth hole is placed on the side opposite of your cheek rest, then it is less noticeable and there is most certainly less air exiting the muzzle helping to reduce the report in that direction.

You can see for yourself by holding a lighter, candle flame, or piece of tissue next to the pinhole and firing a shot to see the deflection.

Regards,

Feinwerk

Thanks for the explanation really helps!

 

[pnwairgunner]

There is no build up of pressure in a shroud. There is a pulse of pressure that is IMMEDIATELY dissipated along with the pellet as it leaves the endcap of the shroud. The vent hole is not there for any safety reason to manage pressure levels, vents are there to try to reduce sound levels and in 20 plus years of airgunning I’ve never seen an airgun that showed any improvement on the sound level by venting the shroud unless foam or felt is used to slow the gas’ escape down.

As I said, tape it up and try it both ways... and then you can choose what sounds best to you. 

 

[Goldwing]

There is no build up of pressure in a shroud. There is a pulse of pressure that is IMMEDIATELY dissipated along with the pellet as it leaves the endcap of the shroud. The vent hole is not there for any safety reason to manage pressure levels, vents are there to try to reduce sound levels and in 20 plus years of airgunning I’ve never seen an airgun that showed any improvement on the sound level by venting the shroud unless foam or felt is used to slow the gas’ escape down.

As I said, tape it up and try it both ways... and then you can choose what sounds best to you.

If I did, it was slightly a duller sound but if I had someone do a blind test it would be indistinuable

I put my index finger near the pin hole and it was very noticeable how strong the puff of air that was coming from it, made me think that they put the hole there with many man hours in taking the time to punch a hole for each length shroud

Thanks

 

[dan_house]

way back when, this was discussed..... 

some have said that the hole in the "device" changes its legal description from a ldc/suppressor etc to a muzzle brake.... 

 

[Goldwing]

way back when, this was discussed..... 

some have said that the hole in the "device" changes its legal description from a ldc/suppressor etc to a muzzle brake.... 

Good one, never would have known that, so it's there for legal reasons over function.... maybe

 

[Sergey1972]

I vote no on changing legal description. Venting the shroud does change the pitch bit not necessarily sound pressure. Makes it sound quieter to us older guys but not the young.

 

[Motorhead]

There is no build up of pressure in a shroud. There is a pulse of pressure that is IMMEDIATELY dissipated along with the pellet as it leaves the endcap of the shroud.

Incorrect .. very incorrect !

When ANY delivery of air or liquid exceeds the rate it enters to rate it exits there WILL BE a pressure rise !

in the case of shrouds or ldc's .... 100's of pounds for a brief moment. ( generally LDC's more so than Shrouds )

It would seem the understanding of what each type devise does & how it does so to mitigate residual noise is misunderstood ?



Lol ... If there was NO pressure rise within it ... a vent hole in a shroud or ldc would not violently squirt out air of it ... DOH !!



No fight here .. being also guilty at times of stating absolutes ... error in speech and structure of what point we're trying to make.

 

[Goldwing]

There is no build up of pressure in a shroud. There is a pulse of pressure that is IMMEDIATELY dissipated along with the pellet as it leaves the endcap of the shroud.

Incorrect .. very incorrect !

When ANY delivery of air or liquid exceeds the rate it enters to rate it exits there WILL BE a pressure rise !

in the case of shrouds or ldc's .... 100's of pounds for a brief moment. ( generally LDC's more so than Shrouds )

It would seem the understanding of what each type devise does & how it does so to mitigate residual noise is misunderstood ?



Lol ... If there was NO pressure rise within it ... a vent hole in a shroud or ldc would not violently squirt out air of it ... DOH !!



No fight here .. being also guilty at times of stating absolutes ... error in speech and structure of what point we're trying to make.

So it would be advisable to bring the shroud back to OEM by completing the job with a drill hole through the CF tube to the inner shroud

Thanks

 

[Motorhead]

 

Grey area ....

If tune is such that it is operating more EFFICIENTLY ? hole may not gain you much. If on the other hand LOTS of air being discharged ( Excessive Dwell ) venting away some pressure within shroud may result in reduced muzzle noise ?



Sadly what you ask has no absolutes & is subject too state of tune of said PCP air rifle.



Scott S

 

[Goldwing]

Well I have 2 FX Crown’s so I’ll see if there’s a difference doing one with a pin hole and one without and listen and watch for any difference 

 

[pnwairgunner]

There is no build up of pressure in a shroud. There is a pulse of pressure that is IMMEDIATELY dissipated along with the pellet as it leaves the endcap of the shroud.

Incorrect .. very incorrect !

When ANY delivery of air or liquid exceeds the rate it enters to rate it exits there WILL BE a pressure rise !

in the case of shrouds or ldc's .... 100's of pounds for a brief moment. ( generally LDC's more so than Shrouds )

It would seem the understanding of what each type devise does & how it does so to mitigate residual noise is misunderstood ?



Lol ... If there was NO pressure rise within it ... a vent hole in a shroud or ldc would not violently squirt out air of it ... DOH !!



No fight here .. being also guilty at times of stating absolutes ... error in speech and structure of what point we're trying to make.

LoL Motörhead!! It would seem the misunderstanding is yours!!

I did NOT say there is no pressure inside a shroud.... I clearly said there is no pressure BUILD UP inside a shroud... it is not a sealed pressure vessel. The pressure is immediately dissipated... etc

Please have another read, my statement is accurate. 

 

[Bigragu]

Just like an exhaust pipe- pressure dissipated and once the old trick potato gets shoved up in there, pressure built up.

But, you can have a mix of both, in where as the force of air being moved is greater than the space within it, and the exit hole, or holes, are either too small, not enough holes, or too far away from where the air started it’s movement, or a mix of all of the above.

Theres static pressure, in like a balloon blown up, fingers closing off the blow up port, and air pressure pushing against the sides.
Then it becomes velocity pressure, once the fingers release the seal and the balloon flies all over the room bouncing against walls and ceiling.