Vented Shroud to Reduce Noise

[Supercharged86]

Well today I went ahead with the vented shroud mod. After drawing out a few possible designs I went ahead with two rows of 7/64" holes (for a total of 9 per side), similar to the ones found on my Mossberg 500 (which has 8 1/8"holes). After several hours of work I can tell you this, it's a very arduous task doing it freehand. So I would suggest doing it on a drll press with a press vise if possible. Not only will this save you time but should give you "perfect" alignment of all the holes. Although, I spent alot of time making sure my pencil guide lines were nice and straight and square with the barrel, by the time I was done drilling, the holes were not perfectly aligned .

At the moment I don't have any way of measuring dB's so I'm unsure whether there is any reduction in sound level out in front of the barrel. However, after several dry fires, there's no question that air escapes from the holes, so this is a good sign. My plan may be to add 4 more holes per side but for now we'll see how this goes. Good luck. Steve

[foxback]

Looking good.

Nice work!

[dwalk]

when you think about it, moderators, shrouds ... all are basically/technically...silencers aren't they?

silencers don't have holes in them that vent to atmosphere do they? not ones that work as intended anyway...

the holes allow gasses/noise to escape to atomshpere...when contained in a "can" they simply 'dissapate' don't they?

all holes do is REDIRECT escaping gasses/sound...another reason a "silencer" exit orifice must be as near to bullet/pellet O.D. as possible...to CONTAIN the escaping gasses/sounds to the rear of the exiting projectile.

the reason some folks vent AF frame bushings is to allow the vented gasses/sounds to enter the frame and dissipate INSIDE the AF frame...NOT to atmosphere.

i believe the depinging operation will aid the standard shroud in noise reduction more than drilling holes in the shroud itself. IMO ,the drilling of holes is more like making it into a muzzle brake than a 'silencer'.

[dogwood]

close, what you want your shroud to do is slow down the escaping air, thus reducing the noise.
I wouldn't have drilled my shroud like that, but I think his primary aim was to redirect the noise.

I would have drilled one small hole at the base of the shroud (near the receiver) and placed something like scotch brite around the barrel to slow the air flow.

you'd want to make it a small hole as the air in the shroud is acting as a "buffer" for the expanding air as it exits the barrel.
Much like you tune a shock by changing the size and number of holes for the oil or gas to flow thru.

[rambosky]

when you think about it, moderators, shrouds ... all are basically/technically...silencers aren't they?

silencers don't have holes in them that vent to atmosphere do they? not ones that work as intended anyway...

the holes allow gasses/noise to escape to atomshpere...when contained in a "can" they simply 'dissapate' don't they?

all holes do is REDIRECT escaping gasses/sound...another reason a "silencer" exit orifice must be as near to bullet/pellet O.D. as possible...to CONTAIN the escaping gasses/sounds to the rear of the exiting projectile.

the reason some folks vent AF frame bushings is to allow the vented gasses/sounds to enter the frame and dissipate INSIDE the AF frame...NOT to atmosphere.

i believe the depinging operation will aid the standard shroud in noise reduction more than drilling holes in the shroud itself. IMO ,the drilling of holes is more like making it into a muzzle brake than a 'silencer'.

I agree.

[Supercharged86]

Well guys the idea here was to convert the unidirectional sound wave (granted it's little, but does exist, to the tune of 85db) into a mutlidirectional (three axis) sound wave. The purpose was to reduce the down range (parallel) noise level..... I agree this is acting more like a traditional muzzle brake like those found on a shotgun, than a silencer, the silencer part is obviously the stuffed baffles. But where there is air flow there is sound waves and I can tell you that there is plenty of air escaping from the four sets of holes. Likewise, it is also louder from the shooting position which tells me one thing. And when I get a replacement db meter I'll be sure to test my theory.

[dwalk]

the scotchbrite idea sounds like a really good idea...

(my son suggested brass wool, too)

that may work well, with or without, vent holes.

since there is no heat involved with airgun barrels during the time of discharge, it would serve to slow/dampen air and noise flow.

methinks there is a trip to the depot/lowes/local hardware store in order...

[rgratton08]

It may not be what you are trying to do but look at the muzzle brake that I put on mine. See I change a few things on my marauder to get pics. This mode dose keep the noise from going down range. it makes it difficult to detect the direction from where the shot came. Also I made a shroud to go over the outside of the brake from a beer can cozy the further reduces the noise.

[Supercharged86]

Any pics? Thanks. Steve

[tjbryner]

I my self vented each baffle into the shroud and each other, My thoughts are to get the air wave to move back towards the frame as fast as I could with out increasing the noise, seems to be working very well so far. No change in POI and seems to be very quite form shoots perspective.

It's rather simple and easy to do with a hand drill or drill press.

Next step will be to use a damping material in the shroud tube behind part #27, this way I can have the air wave go back towards the frame as fast as possible and then dissipate it about 4 inches from the frame.

testing will be done this weekend coming. IF ALL goes well!!

TJ