Long and thin or short and fat? Silencers that is.

[Phil Russell]

Talking silencers here ... what is perceived wisdom for effectiveness? It is clear that silencers come in all different sizes; some longer than others, some fatter. Clearly there is a limit to how fat you can go but what size seems to be the best? Obviously the innards are also part of the equation but for the sake of discussion: for the same innards design would long beat short and fat beat long?
From limited fiddling my guess is that fat beats thin and long beats short.
I wonder if a trombone type adjustable length design would allow silencer tuning to optimise performance for different power levels / calibres?
Monday afternoon musings ...
Cheers, Phil

[angrybear]

I'd guess that it boils down to the internal volume, more air volume = less noise.

but I'd go for longer & thinner because the air is traveling towards the exit hole so the more length to divert it, the better.

[eyebull]

I thought the perceived wisdom was that all other things being equal, volume is key. So with your trombone moddy, the max length would always be the most effective.
Something which doesn't seem to get much attention is the size of the choke. BSA's VC (variable choke) silencer had different sized inserts for .177. 22 and .25, and within the limit of my ability to test it it did seem to make a difference.

[Geezer]

I don’t think you can fully separate out the internal design from the external dimensions. And a lot depends on the volume, pressure and temperature of the air/gas behind the projectile.

In general, the more diameter you have, the better. It appears easier to build an effective short fat suppressor than a long thin one.

But long thin ones can be effective. The well-known Parker-Hale rimfire one (also used on airguns) is a very old-fashioned and quite crude device. But it works well for its intended use.

[McTrucky]

The bang comes from the sudden release of the compressed gas, like popping a balloon. So inside the silencer the thing that stops the bang is slowing that release of pressure. This would be easy if you didn't need to have a .22 sized hole running through it. So the larger the physical volume of silencer the bigger the drop in pressure inside it, meaning a smaller drop when it vents to the atmosphere. So big is better. And the volume increases far more by increasing the diameter, than increasing the length, for all but the shortest of cylinders. So generally, fat beats thin.

The other aspect is slowing the air flow as it vents, so baffle design will affect the noise for any given volume, hence not all silencers are equal, despite appearing identical dimensionally. But the more volume you have inside the silencer, the less important the baffles.

[rapidresponse1]

never thought of it that way before but makes sense

[BC312]

For years i used the Parker Hale design which worked very well especially on firearms, the chamber and baffle method in many shapes and sizes, when i bought a Weihrauch silencer for my air rifles i couldn't believe how quite they were and surprised that inside was a hair curler. Not sure on the logic on this wonderful bit of kit.

[evert]

.... So big is better. And the volume increases far more by increasing the diameter, than increasing the length, for all but the shortest of cylinders. So generally, fat beats thin.
.....

My experience from experimenting with .22 rimfire silencers and making up different baffles and tubes, is that when you reach about 30mm diameter there is not much more to gain with a diameter increase. Baffle construction and length in front of the muzzle is more important than tube diameter when you are past 30mm.