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Firearm silencers (moderator)

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1216864.  Fri Dec 16, 2016 8:09 pm Reply with quote

In 8/16 "Non Sequiturs" it was stated that silencers/moderators don't work. They do. The thing is - you must use sub-sonic ammunition. When fired it sounds like "PFFF" as stated quite correctly in the episode - and IMHO wrongly got buzzed as incorrect !! If you fire full power, supersonic rounds, then the moderator /silencer will suppress the sound of the detonation of gunpowder/propellant however because the projectile is travelling faster than the speed of sound, a very loud sonic boom is evident (very evident) so everybody within about a mile will hear it- thus rendering the moderator useless. Try it yourself - it's the only reason for a moderator to be invented, i.e it works. You just need to keep your bullets slower than 760 mph.

1216881.  Sat Dec 17, 2016 5:05 am Reply with quote

Indeed. The moderator/silencer only slows down the expanding gases to subsonic speeds, if the slug is still supersonic it will make a noise. Silencers on airguns can be very effective due to the lower velocities involved. I haven't seen the episode yet, (distracted by parental care issues) but I hope they mentioned the tendency for Hollywood to show silencers about 20% the size they need to be to remain effective.

Welcome Seabhag!!!

Small point, it would be quite difficult to "try it ourselves" as you need a firearms licence with a special variation to allow use of a moderator/silencer.

1216916.  Sat Dec 17, 2016 9:18 am Reply with quote

...and of course that kind of suppressor doesn't work on automatic pistols, because the reload cycle opens the breech and lets the bang out of the other end.


1216966.  Sat Dec 17, 2016 5:52 pm Reply with quote

Agreed, you only really get a licence for use of a moderator for use with sub sonic rounds for vermin control (rats, rabbits etc) my firearm licence was for a 0.22 rim fire and a 0.243 centre fire. 0.22 subsonic were all you required for rabbits. The 243 ( deer stalking) had a muzzle velocity of about 2900 meters per second, well over the speed of sound and was dangerous at over 5 miles (hence the requirement for a solid background to your target) obviously you didn't aim at objects over 300 to 350 yds. the army SA80 is a 0.223 with slightly lower muzzle velocity but still nowhere near slow enough to suppress.

1216967.  Sat Dec 17, 2016 6:30 pm Reply with quote

Sorry PDR, not exactly true. For a simple blowback pistol that might just be the case, but most semi-auto pistols* are "locked breech" where the slide remains forwards until breech pressure has dropped. This ensures maximum pressure behind the slug, where its needed. The current thinking (when last I looked anyway) is to enlarge the chamber end of the barrel to lock into the ejection port, but the classic John Browning design of the Colt 1911 and all its imitators and derivatives features a rotating cam link which holds the barrel up inside the slide, where mating surfaces lock them together. Many dedicated suppressed pistols will, in fact, incorporate a "slide lock" to make them essentially single shot and ensure that none of the limited supply of subsonic gas is wasted.

Where a silencer definitely won't work is on the revolver the used to illustrate the original question (just saw the XL show). With a revolver, there will always be a gap between the front of the cylinder and the rear of the barrel where supersonic gas will escape. The only exception to this rule might be the Russian Moisin Nagant "gas seal" revolver of (iirc) 1917, where the cylinder was made to move forward on firing, creating a seal on an extended portion of the barrel.

*Certainly anything chambered for 9mm, .380, 10mm, .45acp, .41AE etc. Anything that works on "blowback" will be a low pressure chambering.

1219593.  Thu Jan 05, 2017 6:59 pm Reply with quote

Seabhag wrote:
In 8/16 "Non Sequiturs" it was stated that silencers/moderators don't work.

No, it wasn't. Here's what Sandi said:
No. They cannot eliminate the sound of a gun. They don’t even call them silencers these days, they’re called moderators in the UK, they’re called suppressors in the United States. They can easily be heard if used in public, so criminals never bother with the silencer.

... and she then went on to talk about the Maxim gun.

With all due respect, it's also wrong to say that the moderator is "useless" when used with supersonic ammunition, because it has other uses than simply suppressing sound.

And subsonic ammunition fired through a moderator doesn't make the sound "Pfff" - it makes a noise like slapping two fingers of one hand into the palm of the other - so that was a valid klaxon IMO.

1227522.  Wed Feb 22, 2017 2:41 pm Reply with quote

Mythbusters (an american show) actually tested this. They fired a gun, ON CAMERA, with and without a suppressor. There is a huge difference in the sounds. The suppressor actually makes it sound kind of like a staple gun (that thing you use to secure xmas lights to your house, or permanent carpet to the floor).


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