On ***Law and Order * ** tonight, the bad guy used a “ghetto silencer” on his pistol, which apparently somehow involved the use of an orange soda bottle.
Which got me thinking: How the heck do the silencers work which the Jack Bauers of the world use?
Here’s a pretty gooddescription of silencer action.
Essentially the silencer slows down the shock wave of the rapidly expanding gas as it leaves the muzzel. It does this sort of like the muffler of a car by allowing the gas to expand into a chamber that converts the shock wave into a turbulent flow that slows down before leaving the silencer and dissipates some of its energy as heat rather than sound.
Well, it helps to remember that they aren’t silencers so much as supressors. What they usually consist of is a tube with baffles in it, designed to disrupt the flow of the gasses escaping from the barel of the firearm, making it difficult to pinpoint its location by sound. If you couple this with sub-sonic ammo, you get a fairly quiet firearm, relatively speaking.
I would link to some sites, but they show how to make them, and I think the Reader frowns on such things. 
Are there any recordings that show what a silenced gun actually sounds like? I’ve been told that movie silencers sound nothing like any gun in real life.
A side note: a while back I was shooting some clays with my nephews with 12 gauges, which (to my limited experience) are fairly loud. Meanwhile another nephew is shooting a 22-250 at something. Holy crap. That is one loud mother.
I don’t have any .wav files, but indeed, a suppressed gun doesn’t sound anything like what you hear on the televisor. (Neither does an unsilenced gun…it sounds like a flat “bang” rather than the resonant sound created by foley artists out of a variety of sounds.)
Suppressors, which were invented by Hiram Maxim not to enable criminals but to protect the hearing of the shooter and reduce noise pollution, come in many different designs but the most common primarially uses baffled chambers gto retard the expansion of the gas, along with an end wipe to contain the exhaust. These sound like a wire brush scraped rapidly over metal. Although I’ve never had the chance to fire one I’m told that there are some locked-action .22LR pistols in which the sound of the striker can be heard over the exhaust. On larger bore weapons (which I have heard fired), subsonic rounds (149 grain 9mmP, 180 grain .40S&W, or 230 grain .45ACP) are preferred because the higher velocity rounds make a sonic crack as well as the sound from the exhaust. However, this sound is directed out forward of the barrel, so even with supersonic rounds like the .223 Rem benefit from suppression by protecting the shooter.
Surefire makes what are arguably the best production suppressors on the market (they claim, unlike others, to maintain velocity and actually increase accuracy), but you can make a quite effective silencer for a small bore weapon with a 2litre pop bottle, as alluded in the OP, or an 18" length of PVC and some tennis balls. However, any silencer, no matter how disposable, requires a Class III tax stamp from the ATF as well as meeting state/territorial laws and guidelines. I believe the federal penalty is $10,000 and ten years for each violation, so I wouldn’t recommend playing around.
Stranger
I designed a silencer for a friend’s AR-15 when I was in high school. Another friend built it, and we all fired the rifle with and without the silencer. We also installed a kit and modified some parts to make the AR-15 fully auto.
The silencer was a hollow steel tube about 12" long, with a series of steel washers welded into place along the length. The washers all had different inner diameter openings, and were spaced irregularly – the closest washer to the muzzle was about 1/3 down the tube, the last two were only 2" apart. I believe there were 6 washers altogether, including the front washer. The entire assembly was attached using a clever 3-prong lock affixed to a spare flash suppressor.
In operation, the silencer-equipped weapon’s action made more noise than the rounds. I’m sure that there was still the sonic boom from the bullets – the round was highly super-sonic – but behind the gun it was more ‘snick, whoosh, clunk’ than ‘BANG’. In full auto the action noise was even more pronunced.
The device failed once – while being used by the friend who did the welding. A weld broke on the next-to-last washer, and it turned sideways in the tube. The next round basically exploded inside the tube. Scary, but the tube was way over-spec’d, and contained all the shrapnel. His own fault – bad weld.
The weight of the silencer was a real problem, but also proved to be a benefit when firing in full auto, as it negated any tendency for the muzzle to creep upwards.
We were well aware that all this was highly illegal, not to mention dangerous, but it sure was fun at the time. I believe the device is still in someone’s basement, but since I haven’t seen it in 30 years, I can’t be sure.
A silencer is little more than a muffler you have on your car. Same principle.
This site used to have a better explanation, and may still if you want to poke around, but for a basic explanation read this
Let me get that nit for you. You can’t slow down the shock wave per se, it’s going mach 1 by definition. You can diffuse it by the use of baffles which can delay portions of it thereby a big shock wave into little overlapping ones.
Right, a shock wave is a shock wave is a shock wave. Bad wording. It disperses the flow of the exhaust so it doesn’t come in a single big bang.