.22 silencer baffle hole....

[rhyslightnin]

What's a good usable size hole to put in a baffle washer for a silencer on a .22 air rifle? Now obviously it needs to be bigger than a .22 pellet (5.5mm) so I was thinking 6mm would do it but I've never made one before so I thought I'd ask
Thanks all
Rhys

[Rickenbacker]

I think like 7 or 8mm

[max headroom]

ask nige if he is still on here.

[madcarlos]

I think like 7 or 8mm

Sure mine was 7.6mm .

[Rich]

The effectiveness of the silencer depends in large part on the expansion ratio, the inside diameter divided by the hole diameter. Every millimetre you add to the hole size reduces that ratio quite considerably.

However the practical limit is set by how accurately and precisely you can make all the parts and get them centred and held such that they won't move in service, and how well the silencer is fitted to the barrel. You need the bore axis and the silencer axis to be precisely in line, and this brings in another issue insofar as barrels don't always have the bore precisely on centre, but the silencer position is usually fixed by the barrel OD.

I've tried making silencers with a very tight fit but in practice I've found 7mm to be as close as can be achieved and have no risk of clipping. If it's a silencer you can take apart easily and you don't mind having to make some more baffles to replace the bent ones, try smaller to begin with.

[rhyslightnin]

The effectiveness of the silencer depends in large part on the expansion ratio, the inside diameter divided by the hole diameter. Every millimetre you add to the hole size reduces that ratio quite considerably.

However the practical limit is set by how accurately and precisely you can make all the parts and get them centred and held such that they won't move in service, and how well the silencer is fitted to the barrel. You need the bore axis and the silencer axis to be precisely in line, and this brings in another issue insofar as barrels don't always have the bore precisely on centre, but the silencer position is usually fixed by the barrel OD.

I've tried making silencers with a very tight fit but in practice I've found 7mm to be as close as can be achieved and have no risk of clipping. If it's a silencer you can take apart easily and you don't mind having to make some more baffles to replace the bent ones, try smaller to begin with.

Thanks, good post!
I'm making a primary baffle/stripper for my new R10 so I can utilise the space in a new shorter lightweight carbon shroud I'm going to make. I want to do it with a female 1/2 unf screw thread on the barrel end and a male 1/2 unf on the other (so I can fit a stubby silencer) with the baffle as part of the machined piece. This I'm hoping to drill from the side between the baffle plate and the female 1/2 unf twice at 90° to each other so the air will vent backwards up the carbon shroud hopefully swallowing most of the initial blast, allowing the short silencer to catch the rest.
As it's only 1 baffle probably solid aluminium, I'm hoping it will help keep the rifle short as itl be maybe 10mm from the muzzle but be effective too. I should be able to make it quite tight then just ream it out if it's too close..
What do you think?

[u.k.neil]

I always made mine 6.5 mm mate.


Neil

[max headroom]

Thanks, good post!
I'm making a primary baffle/stripper for my new R10 so I can utilise the space in a new shorter lightweight carbon shroud I'm going to make. I want to do it with a female 1/2 unf screw thread on the barrel end and a male 1/2 unf on the other (so I can fit a stubby silencer) with the baffle as part of the machined piece. This I'm hoping to drill from the side between the baffle plate and the female 1/2 unf twice at 90° to each other so the air will vent backwards up the carbon shroud hopefully swallowing most of the initial blast, allowing the short silencer to catch the rest.
As it's only 1 baffle probably solid aluminium, I'm hoping it will help keep the rifle short as itl be maybe 10mm from the muzzle but be effective too. I should be able to make it quite tight then just ream it out if it's too close..
What do you think?

what are you making. a silencer, a baffle stripper or an air stripper.?

[lensman57]

What's a good usable size hole to put in a baffle washer for a silencer on a .22 air rifle? Now obviously it needs to be bigger than a .22 pellet (5.5mm) so I was thinking 6mm would do it but I've never made one before so I thought I'd ask
Thanks all
Rhys

6.8~7.5 mm. Anything smaller, depending on the power of the gun ofcourse, may make the airflow to around the aperture interfere with the flight of the pellet. Anything larger and the silencing effect is diminished. It is a very complicated affair but for sub12 ft.lbs 7 mm should easily do the job.

A.G

[air-tech]

Not convinced it's critical or needs to be tight - all that a silencer does is slow down the exit of high pressure air, I don't see the relationship between pellet size and exit hole size, it would appear that the muzzle blast has the potential to overtake the pellet anyway. The airflow is almost certainly self disruptive within the chambers, particularly the first one, i.e. it prevents (delays) the exit of high pressure air even with simple disc baffles (and very much so with K baffles). What the first chamber won't do, the second certainly will. I remember having no patience to test a new mod I made for an S10 (Fac, so plenty of air!) so fitted it without any internals at all (but with end cap). It worked amazingly well. Volume i.e. size is the main factor, if a moderator is small then air will still exit it at some pressure, and this makes the mod inefficient. One of mine for .22 was made using washers for 8mm bolts, so probably around 8.5mm. Just to add that the service parameters were well beyond FAC... and the result was silence that the impact at target was louder than the sound at the muzzle.

[Rich]

A properly designed silencer will have the largest chamber nearest the muzzle, that is to say, the first one that receives the air, for the reason air-tech mentions.

I usually build mine with the smallest chamber at the other end.

The length of the chamber governs the frequency where the sound reduction will be at its maximum. Fm = C / (4L) where C is the speed of sound and L is the chamber length, in consistent units of course. The longer chambers give most effect at lower frequencies.

There is a frequency below which this length of chamber will be ineffective. This is the cut-off frequency, or Fc. You can calculate it with reasonable accuracy from the following formula:

Fc = Fm ( 0.003R² – 0.09R + 1.03 ) where R = expansion ratio, ID divided by hole diameter.

There is also a higher frequency at which this length of chamber will be ineffective. That happens at twice the Fm frequency, ie., 2Fm

Using these formulae one can work out the optimum relationship of chamber lengths so that as one chamber tails off in effectiveness the next in size is ramping up to its peak. It turns out to be a Fibonacci sequence, nature's Golden Ratio.

Of course most folk prefer to make the bits and try them out rather than do the maths, it's more fun......

[Rich]

This was one of my most successful designs, fitted to a S200. Yes it's ungainly and no it's not very well finished, I couldn't wait to test it.

http://i.imgur.com/73Pqo4l.jpg

It's a reflex design with four chambers. The overall length is close to 200mm and the OD is 60mm. It's a tube within a tube, the inner tube is 50mm diameter. Air passes along the inner tube and through three baffles. Once it arrives at the last chamber it can escape radially through vent holes in the inner tube and then blow back in the annular void space between the two tubes. You can just see the vent holes at the back.

[rhyslightnin]

This was one of my most successful designs, fitted to a S200. Yes it's ungainly and no it's not very well finished, I couldn't wait to test it.

http://i.imgur.com/73Pqo4l.jpg

It's a reflex design with four chambers. The overall length is close to 200mm and the OD is 60mm. It's a tube within a tube, the inner tube is 50mm diameter. Air passes along the inner tube and through three baffles. Once it arrives at the last chamber it can escape radially through vent holes in the inner tube and then blow back in the annular void space between the two tubes. You can just see the vent holes at the back.

Looks great.. pretty complicated though..
I was thinking about also making a short fat silencer maybe 40mm by 100mm to put on the end and maybe use a wider diameter carbon shroud like a 27mm or a 28mm as the first void....
I've learned now that the barrel under my existing shroud isn't threaded so whatever I do itl be slip on which isn't too much of an issue.
Mmmmmmmmmmmm.... Lots to think about
Thanks all again., Tis very interesting stuff!!
Rhys

Rich you have pm

[bucketboy]

A properly designed silencer will have the largest chamber nearest the muzzle, that is to say, the first one that receives the air, for the reason air-tech mentions.

I usually build mine with the smallest chamber at the other end.

100% opposite to what I have found!


Bb

[bighit]

Not convinced it's critical or needs to be tight - all that a silencer does is slow down the exit of high pressure air, I don't see the relationship between pellet size and exit hole size, it would appear that the muzzle blast has the potential to overtake the pellet anyway. The airflow is almost certainly self disruptive within the chambers, particularly the first one, i.e. it prevents (delays) the exit of high pressure air even with simple disc baffles (and very much so with K baffles). What the first chamber won't do, the second certainly will. I remember having no patience to test a new mod I made for an S10 (Fac, so plenty of air!) so fitted it without any internals at all (but with end cap). It worked amazingly well. Volume i.e. size is the main factor, if a moderator is small then air will still exit it at some pressure, and this makes the mod inefficient. One of mine for .22 was made using washers for 8mm bolts, so probably around 8.5mm. Just to add that the service parameters were well beyond FAC... and the result was silence that the impact at target was louder than the sound at the muzzle.

I bought a bisley moderator for my nephews hw80k. it had no internals at all as you posted above . I added internals but did not notice any difference .

14th pic down on here looks like it http://www.airgunbuyer.com/Showprodu...%20Accessories they sell it for the Tx200HC