Suppressor Engineering 101

Yes, it can be legal to make a silencer. For everything Form-1, from silencer designs that are easily made, to filing forms with the BATF, to 3D modeling. Remember, you must have an approved BATF Form-1 to make a silencer. All NFA laws apply.

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Re: Suppressor Engineering 101

Post by JacksonBrowne »

I really appreciate it -very generous of you.
07/02 SOT
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Re: Suppressor Engineering 101

Post by stimpsonjcat »

Hmmm...when I used the ideal gas laws to do some guesstimating I got politely stomped by the pressure-vessel designers here.

Maybe they left or are sleeping. :mrgreen:
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Re: Suppressor Engineering 101

Post by FastIndy »

Need to be using the ideal guess laws.
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Re: Suppressor Engineering 101

Post by este »

I have to check my math. I did a test 308 with an 16" barrel which gave me a rough chamber and bore volume of 1.46cuin, which is really really rough. Took the 12000psi of a 16" 308, according to a thread here of quickload data. A 2cuin first chamber and a test material of seamless 1.5"OD Grade9 Ti with 80,000psi tensile strength...

By my understanding that was

Pfc = (12000*1.46)/2
Pressure first chamber = 8760
WT = (8760*.75)/(80000*1 - 0.6*8760)

For a pressure-only wall thickness of .088in....... That seems very thick for this application which probably has a generous sized (lower pressure) blast chamber. Shark's Ti 308 tubes are .065 and if I were to call I would think he would suggest it is ok on a 16" barrel. I'm sure I am missing something here. Anyone please feel free to school me, I'll admit none of this is what I would consider a strong point for me.

Mongo, what would you consider is an appropriate design factor of safety for a suppressor?
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Re: Suppressor Engineering 101

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este wrote:I have to check my math. I did a test 308 with an 16" barrel which gave me a rough chamber and bore volume of 1.46cuin, which is really really rough. Took the 12000psi of a 16" 308, according to a thread here of quickload data. A 2cuin first chamber and a test material of seamless 1.5"OD Grade9 Ti with 80,000psi tensile strength...

By my understanding that was

Pfc = (12000*1.46)/2
Pressure first chamber = 8760
WT = (8760*.75)/(80000*1 - 0.6*8760)

For a pressure-only wall thickness of .088in....... That seems very thick for this application which probably has a generous sized (lower pressure) blast chamber. Shark's Ti 308 tubes are .065 and if I were to call I would think he would suggest it is ok on a 16" barrel. I'm sure I am missing something here. Anyone please feel free to school me, I'll admit none of this is what I would consider a strong point for me.

Mongo, what would you consider is an appropriate design factor of safety for a suppressor?

for using Ideal gas law, wouldn't you want to add the volume from the bore when calculating the volume of the blast chamber? so (12,000*1.46)/(1.46+2)= 5064 ?
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Re: Suppressor Engineering 101

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Hmmmm..... I, good sir. Am retarded.
Last edited by este on Tue Nov 09, 2010 11:34 am, edited 1 time in total.
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Re: Suppressor Engineering 101

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este wrote:I have to check my math. I did a test 308 with an 16" barrel which gave me a rough chamber and bore volume of 1.46cuin, which is really really rough. Took the 12000psi of a 16" 308, according to a thread here of quickload data. A 2cuin first chamber and a test material of seamless 1.5"OD Grade9 Ti with 80,000psi tensile strength...

By my understanding that was

Pfc = (12000*1.46)/2
Pressure first chamber = 8760
WT = (8760*.75)/(80000*1 - 0.6*8760)

For a pressure-only wall thickness of .088in....... That seems very thick for this application which probably has a generous sized (lower pressure) blast chamber. Shark's Ti 308 tubes are .065 and if I were to call I would think he would suggest it is ok on a 16" barrel. I'm sure I am missing something here. Anyone please feel free to school me, I'll admit none of this is what I would consider a strong point for me.

Mongo, what would you consider is an appropriate design factor of safety for a suppressor?
Well as mentioned before, for pressure vessels they use 3 to 4 which I think is good. I checked your math and your calculations that you have shown are right except as noted in the above post, you did not add the volumes. You first chamber is too small and should be increased in my opinion. Remember QD suppressors have more volume in the first chamber than it looks due to the mount area. Another problem, you are using the strength of the Ti at room temperature. It will degrade in strength even as low as 300F which a bolt action can will reach easily after 5 - 10 shots.


Also as I said earlier, the idea gas law is really rough in this case and you are not going into a sealed area so there is fudge in there as well. The 308 short barrel guns can have quiet a bit of powder still burning in the suppressor so shorter the barrel the worse the approximation via ideal gas law. I have not covered this, but using a muzzle brake will increase gas impingement pressure on the walls of the suppress and can cause distortion.

I have been real conservative in the information posted to help keep you guys safe and to save you money since blowing cans for R&D is expensive. I can't remember how many cans AAC destroyed doing research for the military but it was a lot and this is why they are now light yet very strong.
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Re: Suppressor Engineering 101

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este wrote:Hmmmm..... I, good sir. Am retarded.

I did the same thing on my thermodynamics test about 2 weeks ago( entropy change from flow between 2 pipes.) at least you aren't getting graded... lucky bastard
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este
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Re: Suppressor Engineering 101

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Mongo wrote:Well as mentioned before, for pressure vessels they use 3 to 4 which I think is good. I checked your math and your calculations that you have shown are right except as noted in the above post, you did not add the volumes. You first chamber is too small and should be increased in my opinion. Remember QD suppressors have more volume in the first chamber than it looks due to the mount area. Another problem, you are using the strength of the Ti at room temperature. It will degrade in strength even as low as 300F which a bolt action can will reach easily after 5 - 10 shots.


Also as I said earlier, the idea gas law is really rough in this case and you are not going into a sealed area so there is fudge in there as well. The 308 short barrel guns can have quiet a bit of powder still burning in the suppressor so shorter the barrel the worse the approximation via ideal gas law. I have not covered this, but using a muzzle brake will increase gas impingement pressure on the walls of the suppress and can cause distortion.

I have been real conservative in the information posted to help keep you guys safe and to save you money since blowing cans for R&D is expensive. I can't remember how many cans AAC destroyed doing research for the military but it was a lot and this is why they are now light yet very strong.
Thanks for getting back to me on that. Yea, I feel like a bonehead for forgetting to add that. I've done stupider things I suppose.

Do you have any idea how I could find out the strength of a metal at a temperature? I've been looking for that for awhile. I can find tensile and ultimate, but I can't seem to find what temp those are at (I assume room), or how those scale.

As for the sealed area vs a silencer thing. Yea, I've been considering that. Even if you imagined the bullet as perfectly plugging the blast baffle, the issue would become how long does the first chamber need to be able to hold this 3000-8000 psi charge? I assume there is a difference between holding 8000psi for a few milliseconds vs years. This I guess is the basis of the "silencer is not a pressure vessile" argument. I would think this difference would be more than what I would consider fudge factor, it seems VERY significant but I really don't know anything about anything.

I'm absolutely understanding about being conservative and I think that's the right choice. However, if I take the above numbers and double the size of the first chamber to 4cuin, that's a pressure of 3200. Reasonable for sure. That's makes the required wall thickness a guess of .030, very thin, but with a factor of saftey of 3 that's a wall thickness of .090... That's thicker than anyone is using for a 308 can. I would be shocked if the 300-SD which is supposed to handle 300WSM had a wall thickness of .090. So I understand the conservativeness, but it's slightly confusing looking at practical examples.
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Re: Suppressor Engineering 101

Post by Bowen1911 »

este, looking in my strength of materials book, the tensile stress from the hoop stress doesn't increase linearly with relation to the wall thickness for cylinders.

hoop stress= pressure* inner radius^2/(outer radius^2-inner radius^2) * (1+outer radius^2/inner radius^2)

granted it is near linear due to it being thin walled. ----- hoop stress = pressure* average radius/ thickness

the difference in radius is less than 10 percent, so the book says to use the thin walled formula.

I miss 8th grade algebra.


I personally am curious as to how dimensions are determined, so if I find some more info i will put it here asap.
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Re: Suppressor Engineering 101

Post by Mongo »

Unfortunately the only source I know of that has tensile stress degradation with temperature is the ASME Boiler and Pressure vessel Code and the ASME Piping Codes. Both codes have the safety factor built into the numbers listed for allowable tensile strength at each temperature but the safety factor varies between the piping and pressure vessel codes. The piping is less conservative on the safety factor but there is also allowable stresses published when doing design by FEA but this too has restrictions since at temperatures above 700 you must to cyclic analysis. Sorry if this sounds overly complicated and technical but it is meant to be used by engineers and that why we get paid the medium bucks. As for buying the code, it is expensive and is updated ever 2-3 years, you might find a old copy for cheap but usually the old versions are retained in case the vessels of that year are modified in the future.
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Re: Suppressor Engineering 101

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Mongo wrote:Sorry if this sounds overly complicated and technical but it is meant to be used by engineers and that why we get paid the medium bucks
you make me want to change my major.
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Re: Suppressor Engineering 101

Post by Jimmy_Jr »

Bowen1911 wrote:
Mongo wrote:Sorry if this sounds overly complicated and technical but it is meant to be used by engineers and that why we get paid the medium bucks
you make me want to change my major.
Do it. DO IT! That's what I did. :wink:
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Re: Suppressor Engineering 101

Post by Bowen1911 »

Jimmy_Jr wrote:
Bowen1911 wrote:
Mongo wrote:Sorry if this sounds overly complicated and technical but it is meant to be used by engineers and that why we get paid the medium bucks
you make me want to change my major.
Do it. DO IT! That's what I did. :wink:

change it to what. I am already Mechanical Engineering.
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Re: Suppressor Engineering 101

Post by stimpsonjcat »

este wrote:

I'm absolutely understanding about being conservative and I think that's the right choice. However, if I take the above numbers and double the size of the first chamber to 4cuin, that's a pressure of 3200. Reasonable for sure. That's makes the required wall thickness a guess of .030, very thin, but with a factor of saftey of 3 that's a wall thickness of .090... That's thicker than anyone is using for a 308 can. I would be shocked if the 300-SD which is supposed to handle 300WSM had a wall thickness of .090. So I understand the conservativeness, but it's slightly confusing looking at practical examples.
My home brewed 308 can is 0.12" thick for the blast chamber.

The can came out weighing almost exactly what the AAC 300WSM can weighs in at...which is quite heavy.
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Re: Suppressor Engineering 101

Post by ohnomrbillk »

Wonderful work, Mongo. Thank you
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Re: Suppressor Engineering 101

Post by pneumagger »

a GREAT site outlineing the mechnical properties of just about any alloy of metal... including teperature effects on the modulus.
http://www.knovel.com/web/portal/basic_ ... bookid=754

edit: LOL - I spelled outlining wrong above. :lol:

Easy way to spot engineers... find smart people who can't spell. You've either found a mathematician or an engineer. Next, ask them how to say "1/4-20". If they respond "one fourth minus twenty" or "negative 19.75" you got a math major. If they respond "'quarter-twenty" you've got yourself an engineer.
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Re: Suppressor Engineering 101

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pneumagger wrote:a GREAT site outlineing the mechnical properties of just about any alloy of metal... including teperature effects on the modulus.
http://www.knovel.com/web/portal/basic_ ... bookid=754

edit: LOL - I spelled outlining wrong above. :lol:

Easy way to spot engineers... find smart people who can't spell. You've either found a mathematician or an engineer. Next, ask them how to say "1/4-20". If they respond "one fourth minus twenty" or "negative 19.75" you got a math major. If they respond "'quarter-twenty" you've got yourself an engineer.
Quarter inch, 20 TPI? :?
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Re: Suppressor Engineering 101

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LavaRed wrote:
pneumagger wrote:a GREAT site outlineing the mechnical properties of just about any alloy of metal... including teperature effects on the modulus.
http://www.knovel.com/web/portal/basic_ ... bookid=754

edit: LOL - I spelled outlining wrong above. :lol:

Easy way to spot engineers... find smart people who can't spell. You've either found a mathematician or an engineer. Next, ask them how to say "1/4-20". If they respond "one fourth minus twenty" or "negative 19.75" you got a math major. If they respond "'quarter-twenty" you've got yourself an engineer.
Quarter inch, 20 TPI? :?
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Re: Suppressor Engineering 101

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LavaRed wrote:
pneumagger wrote:a GREAT site outlineing the mechnical properties of just about any alloy of metal... including teperature effects on the modulus.
http://www.knovel.com/web/portal/basic_ ... bookid=754

edit: LOL - I spelled outlining wrong above. :lol:

Easy way to spot engineers... find smart people who can't spell. You've either found a mathematician or an engineer. Next, ask them how to say "1/4-20". If they respond "one fourth minus twenty" or "negative 19.75" you got a math major. If they respond "'quarter-twenty" you've got yourself an engineer.
Quarter inch, 20 TPI? :?
thats what i say
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Re: Suppressor Engineering 101

Post by Historian »

Este, your " ... I did a test 308 " brought a light to my eyes but when I read in detail (guys hate to read, give us pictures)
I realized that it was not about the 308 test that I took yesterday, $25K, 42,000 miles.

On a Magnum, no less, 'Higgins'. :)

Example of the sound I am talking about on
Youtube: << http://www.youtube.com/watch?v=9UCYM0hy ... re=related >>

Thank you for your insightful information.
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Re: Suppressor Engineering 101

Post by ohnomrbillk »

This is awesome. Thank you
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Re: Suppressor Engineering 101

Post by jdj »

Mongo wrote:As for buying the code, it is expensive and is updated ever 2-3 years, you might find a old copy for cheap but usually the old versions are retained in case the vessels of that year are modified in the future.

You would think that these material properties for different alloys would be freely available electronically in this day and age, just like the PDR is available as a drug reference (although this might be highly government subsidized by the FDA and or Drug companies).

http://www.pdr.net/drugpages/concisemonographlist.aspx
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Re: Suppressor Engineering 101

Post by fdv99 »

What would be the best way to determine the chamber volume for a 5.56 chamber? just the volume of a unfired case? or guess using calipers inside the chamber?
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Re: Suppressor Engineering 101

Post by wolf »

Eureka :wink:

Archimedes

This exclamation is most famously attributed to the ancient Greek scholar Archimedes; he reportedly proclaimed "Eureka!" when he stepped into a bath and noticed that the water level rose — he suddenly understood that the volume of water displaced must be equal to the volume of the part of his body he had submerged. This meant that the volume of irregular objects could be measured with precision, :wink:
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