I have a few shrouds with vent holes near the rear and a couple without. Does the vent hole reduce the sound or turbulence behind the pellet associated with the shot?
Shroud vent holes
- Thread starter Corvid_hunter
- Start date
I use vent holes in the rear of the shroud so it can use the whole shroud my thoughts are that if it's sealed off kinda airlocks and doesn't use the whole thing also seems to make it quieter at the muzzle in my opinion but I could be totally wrong to
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Smaller shroud diameters / volume can benefit from vents in reducing muzzle turbulence, noise not so much
Lowering noise as well muzzle turbulence is best dealt with by gaining efficiency with lower valve dwell.
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Check out Hajimoto's YouTube video regarding adding vent holes to original Umarex Gauntlet shroud. I added vents, didn't notice difference, later inspection to Mr.Clean buffer did reveal staining so air is venting. WM
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I have two FX shrouds, there were no holes so I drilled them. The original built in air stripper breaths easier, I can see a lead coloration around the hole edges. Also I feel kind of lower frequency pitch coming out at rear.
I have seen some fairly sophisticated internal air strippers from UK for these FX shrouds, I may get one to try next time something is coming in from that island.
I have seen some fairly sophisticated internal air strippers from UK for these FX shrouds, I may get one to try next time something is coming in from that island.
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Shroud vent holes may reduce report as measured near the muzzle, while increasing it to the side. I prefer less noise at my ear.
Proponents of rear shroud vents will tell you to stuff the rear of the shroud with felt of foam, to reduce lead dust blown into your face. That stuffing essentially blocks off the rear shroud vents and the benefit you get from the stuffing in sound reduction is two-fold: Less sound leaks out the rear vents, and the stuffing reduces the reflected pressure waves bouncing forward from rear end of the shroud. The stuffing will do as well, without the holes in the shroud...
Those who are concerned about the rear shroud spacing "filling up", guess what happens to the front of the shroud or moderator space? Air flows in and compresses to higher than ambient pressure; then leaks down via the baffle bores to return to ambient pressure a short while later.
The same thing happens to the air in the rear of the shroud. It compresses, then leaks out the front end of the shroud, and the mod - if you have one, a short while later.
If you want enough rear shroud vent flow area to make a difference in "flow through", without leaking sound, then a swarm of 0.5 to 1 mm holes should do it. Like the fine mesh Huggett uses on their shrouds and mods. Drilling one or two large holes either can't flow enough air to make a difference in the 0.2 second time frame where most of what is going to happen sound wise, happens; or the holes will be so large that it lets sound out, almost like the front cap bore of the shroud or mod...
Proponents of rear shroud vents will tell you to stuff the rear of the shroud with felt of foam, to reduce lead dust blown into your face. That stuffing essentially blocks off the rear shroud vents and the benefit you get from the stuffing in sound reduction is two-fold: Less sound leaks out the rear vents, and the stuffing reduces the reflected pressure waves bouncing forward from rear end of the shroud. The stuffing will do as well, without the holes in the shroud...
Those who are concerned about the rear shroud spacing "filling up", guess what happens to the front of the shroud or moderator space? Air flows in and compresses to higher than ambient pressure; then leaks down via the baffle bores to return to ambient pressure a short while later.
The same thing happens to the air in the rear of the shroud. It compresses, then leaks out the front end of the shroud, and the mod - if you have one, a short while later.
If you want enough rear shroud vent flow area to make a difference in "flow through", without leaking sound, then a swarm of 0.5 to 1 mm holes should do it. Like the fine mesh Huggett uses on their shrouds and mods. Drilling one or two large holes either can't flow enough air to make a difference in the 0.2 second time frame where most of what is going to happen sound wise, happens; or the holes will be so large that it lets sound out, almost like the front cap bore of the shroud or mod...
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I believed in venting shrouds at one time. Like Motorhead said, it depends on the shroud diameter and the caliber/air your pushing. I believe, but don’t quote me, I kept the accumulated size of my holes half the caliber of the gun. Recently the vented shroud on my RTI in compact .25 just started getting on my nerves. Not to mention noticing lead dust on my glasses. So I built an insert that goes in the back of the shroud. It still vents, it’s just not venting like a Harley.
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I have made lots of shrouds for various guns and no longer bother with back venting as it makes very little difference to how quiet the shroud is I prefer to treat a silenced shroud as a moderator that's incorporated into it some of my shrouds for guns like AA FTP900 and HFT500 which are very loud, and I can't use larger diameter due to cylinder proximity I have managed to get them to an acceptable level and still keep the overall length as short as possible,
I have found that in some guns It's not just the size of the shroud, it also about the firing cycle of the gun and just how it releases the air to propel the pellet.
I have found that in some guns It's not just the size of the shroud, it also about the firing cycle of the gun and just how it releases the air to propel the pellet.
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What did Motorhead say? Something about control of valve dwell? That is the key to tuning in the first place isn't it? And balancing all settings to mesh with valve dwell? From one of low experience in physically tuning but a few years of trying to learn my particular PCPs that seems to be the whole nut to crack. All those things with pellet fit and bore condition/twist rate per pellet style. DON'T FORGET TO CLEAN THE BORE WHEN PRECISION GOES DOWN THE TUBES. BE Well Brothers, Bandito.
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I always find that making and fitting an SSG to most guns will quieten them down anyway without adding extra silencing, which shows that speeding up the valve closure and eliminating hammer bounce is a definite for a quiet gun.
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SSG spring stop guide, a device that stops the hammer spring before it reaches full extension which removes the pressure from the hammer when it hits the valve, so the hammer can't bounce and reopen the valve wasting air and in some cases causes pulsing before the pellet has left the barrel.
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They are usually homemade I know of no place that sells them, there are a couple of new guns that actually use this system, I believe the Epic uses an SSG.
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Most quality guns don’t require us to build a SSG, HDD or install a SSS. Those are all terms that were universally understood when we all had unregulated guns or were installing regs in unregulated guns. I haven’t built one in years. But every Kral or Benjamin I’ve ever owned or still own has one. They are a difference maker when you are dealing with a globetrotter hammer.
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