"corners should be round" Theo Evo .22/.177 - Meopta 6x42, DS huntsman classic .20 vortex razor LH 3-15x42 under supervised boingrati tuning by Tony L & Tinbum, HW77 forest green - Nikon prostaff 2-7x32 plex.
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
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.
**WANTED**: WEBLEY PATRIOT MUZZLE END; Any Diana/Original mod.50 parts, especially OPEN SIGHTS
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......
www.shebbearshooters.co.uk. Ask for Rich and try the coffee
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.
www.shebbearshooters.co.uk. Ask for Rich and try the coffee
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
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
"corners should be round" Theo Evo .22/.177 - Meopta 6x42, DS huntsman classic .20 vortex razor LH 3-15x42 under supervised boingrati tuning by Tony L & Tinbum, HW77 forest green - Nikon prostaff 2-7x32 plex.
I have to disagree with almost everything I'm afraid, I make my on mods and shrouds, tight tolerances of baffle washers makes a huge difference.
I put the first baffle washer close (15-20mm from muzzle) I make it .25mm and no more than .5mm bigger than pellet dia and thicker than the pellet is long. My reasoning is, as the pellet exits the muzzle and enters the baffle it effectively bungs up the hole causeing the escapeing air from the barrel to expand into the first chamber without being able to overtake the pellet.
The pellet enters the second chamber (20-25mm long) the air follows (now moving more slowly) and again the pellet gets to the baffle before the expanding air arrives. This process continues (chambers getting progressivlely longer) until the pellet exits the endcap. Tight tolerances between baffle and pellet also cause the expanding air to be pushed deeply into the felt wadding slowing the air still further.
For those reasons, A well made mod might not be that effective without a pellet, massively better with.
Fac is a different ball game, I have made a long reflex mod for a 60fte .25, the more air that was blasted through it, the better it became, it was easily as good as a HW. on a sub 12
**WANTED**: WEBLEY PATRIOT MUZZLE END; Any Diana/Original mod.50 parts, especially OPEN SIGHTS
Dry fire the gun and listen to noise level, now stick some duck tape over thr endcap blocking up the exit hole, dry fire the gun again. With a well made mod/ shroud there should be very little difference in noise output between the two.
I want to strip the muzzle blast using the shroud as a first chamber then my huggett belita as the rest. It's to reduce muzzle noise, I'm hoping the shroud section will make up for the belita not being as effective as a full length mod & It'll also mean if I want to make the muzzle shorter by removing the belita and using the original muzzle brake it will have some (I realise not all) reduction in noise.
So IL have a short semi quiet rifle, STD length quiet rifle or I can use somthing larger like a VC mod to make it super silent.
Hope this answers your question..,
Rhys
"corners should be round" Theo Evo .22/.177 - Meopta 6x42, DS huntsman classic .20 vortex razor LH 3-15x42 under supervised boingrati tuning by Tony L & Tinbum, HW77 forest green - Nikon prostaff 2-7x32 plex.
In my experience having a small first chamber can cause a kind of muzzle flip. Acoustically it doesn't matter which order the chambers are in. The idea of the long baffle works.
Agreed, you have to fire a pellet to make any judgement, likewise with no silencer many rifles are a lot noisier if fired empty.
In an ideal world one would measure the acoustic signature and design the silencer to take out the offending frequencies.
www.shebbearshooters.co.uk. Ask for Rich and try the coffee