How do suppressors work?

scythefwd,

true, but for the purpose of trying to explain that a supersonic bullet doesn't get magically slowed down i chose to neglect that
When I say remove all pressure behind the bullet, I mean that it the pressure is equalized with the atmospheric pressure. But yes, there will also be drag (=opposite force) by the bullet moving through the air

The MP5SD suppressor does have a number of ports in the barrel just in front of the chamber for velocity control. It's unusual and atypical.

I play with suppressed .300 WM and .338 rifles on a fairly regular basis. A typical .300 WM meters around 165 dB unsuppressed, and around 141 dB suppressed. That is with a muzzle velocity of 2950 with a 190gr bullet.

Now, if I can find it, there is a chart that shows that the crack from a supersonic .30 cal bullet is in the 140 decibel range (sound metering for impulse noise is complicated, and very condition dependent) ah here it is...about 1/3 of the way down the page. http://guns.connect.fi/gow/highpow.html Actually, that whole article is pretty good.

The sound from the report is caused by the velocity of the propellant gasses venting. The velocity is dependent on the pressure the gas is at. A suppressor provides a volume for the gas to expand into, and cool down, therefore reducing pressure and velocity of the gasses coming out of the muzzle.

anyway pat, you are a little bit right, but mostly wrong.

So they are using porting on the barrel instead of the suppressor to manage velocity?

Exactly!

Here's one for everyone following this topic.
What are the reasons for using supersonic bullet out of a suppressed weapon?
I'll post my answer later.
Let's see what turns up.

The advantage is range and trajectory. You use the suppressor to protect your ears.

The sonic boom from the bullet breaking the sound barrier isn't easy to place, and is only heard from very short distances away. Frequently people will guess the wrong direction entirely when hearing a suppressed weapon being fired with supersonic rounds.

There is an energy advantage to using supersonic rounds, and besides... they'll hear the action working anyways

This thread has some good discussion, I'd hate to have to lock it because some folks can't play nice.

One thing that the local suppressor crowd has told me:
Youtube videos don't do suppressor justice as far as the sound. It has to do with the microphone & sound recording on cheaper video.

Part of the local suppressor crowd included a suppressor mfgr. Another in the crowd was a professional video/photo guy.

My best explanation of how a suppressor works is you trade the intensity of the escaping gas for duration. You spread the gas out over more area for more time.

Personally I have no use for a suppressor. I find them interesting and like to learn about them. I just don't shoot in any venue that would allow using one. Maybe I just have not reached the point where the $$$ is available for such an item.

scythefwd, you got it faster than I thought anyone would.

ditchtiger - which answer? Guessing on what I was able to read last night about not sourcing the boom. I knew they aren't audible from very far away when they are small objects.

Others are simple physics and common sense.

pat, what type of engineers are you and your room mate? Mechanical, structural, aeronautic, social, electrical? Just curious.

there were three of is last night discussing this and one was civil (though this really has little bearing on the physics classes and such that you are required) our friend is a mechanical engineer (done with school alltogether) and i am a construction management major which though is not engineering i still have to take alot of classes and such that deal with the environments forces on an object.

And to all of you out there that want to "resort to name calling" if you cant handle a debate fueled by science, and opinion just dont read it anymore. Fact of the matter is there is merit to both sides of the argument, the projectile doesnt slow as much as i previously thought, but it does whether caused by the barrel being shortened reducing the amount of time the environment has to impact the projectile, or by loss of energy due to lost pressure behind it there is no doubt that this has an impact. I reach out to you to please private message me if you want to get in a name calling contest. Scythe and i have had some pretty intelligent dialog if you would like to "stupid up the conversation" go for it just do it elsewhere. Thank you.

IF your looking for advice on how to build one, my advice is don't, it's just a hair illegal without the stamp

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Panoz77,

It is a pity that anyone would come to any gun forum and try to talk someone out of making or owning any legal firearm. While you might not be actively discouraging firearm ownership, you certainly are not encouraging it at all in your first post on this thread. While silencer ownership is routine in the USA, the penalties are very severe in comparison to other victimless crimes when ATF authorization is not obtained or the tax is evaded.

The legal requirements for owning a silencer at the federal level are simple and easy to accomplish. It is easier than getting a first time driver’s license or a marriage license. Anyone who can own a firearm can own a silencer. There are no federal laws making silencer illegal to own, there are just a few laws to contend with. All it takes is to be 18 years old (21 to get from a dealer), fill out the ATF form 4 (form 1 to make), form 5330.20, fingerprint cards, photos and a check for $200. The biggest hurdle for some is obtaining the local sheriff’s signature on the ATF form 4. A trust or corp. can be used to own the silencer then the sig, prints and photos are not required. It is a very easy and routine process for those who live in one of the 37 states that allow unlicensed civilians to own them.

Ranb

...but it does whether caused by the barrel being shortened reducing the amount of time the environment has to impact the projectile, or by loss of energy due to lost pressure behind it there is no doubt that this has an impact.

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Adding a suppressor doesn't shorten the barrel. The powder still has the same amount of time to burn whether the suppressor is attached or not. Thus the same amount of pressure will be produced behind the bullet and the same velocities will be reached.

When a bullet leaves the muzzle all of the expanding gasses are free to go out in all directions, thus there is no more pressure behind the bullet pushing it forward. By attaching a tube onto the end of the barrel you don't really cause less pressure to be produced than already would be if there were no suppressor. The tube (suppressor) simply slows and redirects the expanding gasses exiting the muzzle.

Perhaps because of the engineering classes you're overthinking things. I've been guilty of doing the same myself. Often, though, the simple answer is the best.

yeah average but it was stated earlier that many people who use suppressors often shorten the barrel. Im still thinking that something with the suppressor would have to effect the flight of the bullet. We pulled out quite a few physics books and such last night and our engineer friend actually did the math on a couple models (this is waaay past me and i have no idea how it works) and she could explain to us that through the math that she did the forces of the gases escaping around the bullet and through the baffles would effect the stability of the projectile. I am pretty much past the argument and am now more on the mission to run through all the variables that a suppressor can cause and see what it can to do a bullet.

I design and make silencers as a hobby. I have little education past high school, but I have a very good idea of what works and what does not. I have designed and built nine silencers so far, for 22lr to .338 magnum and .510 caliber. All of them work well.

Gun silencers in their simplest form are merely enclosed tubes attached to the barrel muzzle. The gun powder gases enter the tube to expand and cool before being released to the outside atmosphere. It is that simple, cool and expand, just like a car muffler.

The goal for most who design silencers is to make the silencer reduce noise as much as possible. Durability, compact size, and minimizing the affect on accuracy and point of aim are other major considerations. This is where the internals design plays a major role. A good silencer will reduce noise intensity by 20 to 30 decibels. Since decibels are a logarithmic function of sound pressure, 20-30 decibels is a 100 to 1000 times factor change in noise intensity. This is equal to a four to eight times reduction in loudness. Frequency, noise duration and shooting environment all contribute to how differently a person hears the noise of a suppressed firearm. Ultimately the usual goal of the silencer designer is to allow the safe shooting of the weapon without hearing protection. Sometimes they are marginally or not nearly successful.

There are a few designs that work very well at reducing noise, but degrade accuracy and/or velocity. A silencer that uses wipes is one of these. Imagine a 9mm pistol with a threaded barrel that has a tube of 1.25" by 7" attached to it. On the inside are rubber disks with X shaped slots cut in them. The disks are held about an inch apart by spacers that tightly grip the outside edges of the wipes. A wipe suppressor is typically very good at suppressing the noise, but only for a short time. Since the bullet contact the wipes, they damage the wipe with each shot and accuracy is degraded. After several dozen rounds, large holes are blown into the wipes and they reduce noise by much less than when new. I have only seen these types of silencers for 9mm and less powerful cartridges. Wipes are the only silencer part the ATF allows an unlicensed owner to replace without paying another $200 tax.

Another type of silencer that reduces bullet velocity is that which uses a ported barrel as part of the silencer. Many integral silencers that are built as part of the barrel use ports. These silencers can be very effective at reducing noise, but some of them such the 22lr ones can reduce velocity too much. I converted a Lee Enfield rifle to a near Delisle carbine configuration. I removed the spacers and stacked the baffles at the end. I ported the barrel and profiled it to fit the silencer internals. 230 grain ammo that shot 850 fps in a five inch 1911 moved about 1150 fps in the unported Enfield barrel and 1040 fps after the barrel was ported.



the top drawing shows the silencer set up for a 510 whisper, the middle drawing for the 45 ACP Enfield. Porting the barrel can be a very effective method of further reducing the noise on some suppressed guns.

Ranb

she could explain to us that through the math that she did the forces of the gases escaping around the bullet and through the baffles would effect the stability of the projectile. I am pretty much past the argument and am now more on the mission to run through all the variables that a suppressor can cause and see what it can to do a bullet.

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Your friend is correct. Changing anything about the barrel will affect the bullet flight path. The barrel whips around when the gun powder burns; short and stiff barrel whip less. If the barrel crown is perfect, the gases will be released exactly even around the base of the bullet as it exits the barrel thus minimizing the disruption of the bullet flight path.

Attaching a weight (silencer, brake, flash suppressor) to the end of the barrel always changes the flight path, even if it is too small to measure. Attaching a silencer that extends over the barrel can help improve accuracy in a small way. If the silencer screws on at the muzzle and puts tension on a shoulder inches in back of the muzzle threads, then this tension can improve (allegedly) accuracy.

One thing a silencer can do to degrade accuracy is baffle strikes. If the bullet touches the baffle while it passes through, then it will yaw and at the very best will impact farther but consistently from the center. It usually makes the bullet yaw and tumble resulting in a total miss unless you are shooting at close range. the worst case scenario is that the bullet completely wrecks the silencer, pieces break off and go downrange and the barrel is ruined. This has yet to happen to me although I have had minor baffle strikes that made the bullet impact 6 feet low at 100 yards.

As for changing bullet velocity, a silencer equipped with baffles that do not touch the bullet can exhibit something called suppressor boost. As the gunpowder gases are contained in the silencer body for a brief fraction of a second, they can still continue to push on the bullet a small amount. Some people have reported seeing 10-40 fps increases in speed when measuring on a chronograph (I have also), but this increase in speed is significant only in that it shows the bullet is not slowing down inside of the silencer.

A silencer can degrade accuracy (according to some experts) by disrupting gas flow across the bullet's path when using asymmetrical baffles, especially an asymmetrical blast (first) baffle. This is something I have not been able to observe myself. Since I think accuracy is more import than suppression, my blast baffles are always symmetrical.

Ranb

Another kind of silencer is one that merely attaches to the muzzle. No barrel porting, no wipes, just metal baffles and spacers in a tube. The most common baffles types are those shaped like a K, or an M, or a cone, or simply flat washers separated by spacers.


Here is a 22 caliber silencer for an AR-15 with 60 degree stepped cone baffles. Most cone baffles are separated by spacers.


Another with K baffles. The K baffles are self aligning and do not require spacers. The muzzle brake mounts to the silencer at two places for good alignment. The muzzle brake is a tight fit along the exterior to help ensure it is aligned to the bore. The silencer bore is between .250" to .300" to aid in suppression. The tighter the bore makes for better suppression but could more likely result in baffle strikes.



What I made for my 9mm Browning. I shoot cast 147 subsonic in it which really leaves lots of gunk behind. Threaded end caps allows me to clean it out after a few hundred rounds.



Compare this to a silencer that extends over the barrel. I was not able to make threads that were aligned well enough to the bore to ensure properly silencer alignment, so I moved the front sight back to allow a two point mount.

Ranb

Part of my collection. Many more hosts then silencers, so I make them to fit several firearms in most cases.

Ranb

thank you ranb. I couldnt find any sets of prints or plans to look at. I see that i was a little misinformed about how these things were made. My friend now is really fired up and swears that she is going to get her hands on some plans and do all the math to show what will happen to a bullet when fired through each of these suppressor types and to what degree it will happen based on a 308 bullet.

If anyone has solidworks (or similar) simulation files, i'd be very interested

Ranb, you mentioned baffle-strikes when using too narrow or off-center baffles. What are the possible consequences of this happening? I imagine a ruined or very unstable bullet, but what will it do to the suppressor and the functioning of the gun during follow-up shots?

My friend now is really fired up and swears that she is going to get her hands on some plans and do all the math to show what will happen to a bullet when fired through each of these suppressor types and to what degree it will happen based on a 308 bullet.

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That sounds good. If there is one thing missing from silencer tech it is the science of noise reduction and how to predict how a new design will work. If she has anything of substance, then I hope she posts it on the forum at http://www.silencertalk.com . Her results might generate much disscussion over there.

Ranb

The results of my MINOR baffles strikes have been dented baffles and end caps. This resulted in completely missing the target. I was able to repair the end caps with a hammer. My 9mm and 22lr silencers unscrewed a bit while firing and drooped which is why I got the baffle strikes. My 510 whisper can was used with some new cast bullets I was trying without gas checks. This made them yaw 90 degrees within 25 yards. I did not find this out until I was investigating the cause of the baffle strikes.



Above is a photo of a quality silencer that was destroyed by a single baffle strike. If I remember correcctly it was caused by improper mounting. I do not know if the barrel was damaged or not.

Ranb

http://www.youtube.com/watch?v=SLGrznbs3Mw

I can't believe nobody has posted something like this yet. The effects of a suppressor on standard and subsonic ammunition, all in one video. It's not mine, I just did a search on youtube for "rifle suppressor".

the holes in the baffles need to be larger than the bullet to avoid baffle strikes. the longer the bullet, the bigger the holes need to be, because of yaw. it can take nearly 50 yards for the bullet to fully stabilize. M855 has been measured at almost 9 degrees yaw in some cases...