Using the Ideal Gas Law to "scale down" a suppressor

[BungieCord]

The Ideal Gas Law gets mentioned quite a bit in this forum but I can't find any information on just how it applies to design, but I have my own ideas, so I'm going to take a swing at it.

If I want to "scale down" the design of a store-bought suppressor for use on a Form1 suppressor for a less powerful cartridge, would it produce valid numbers if I were to use static pressure values (as predicted by QuickLoad) multiplied by the bore & chamber volumes on the theoretical hosts?

As an example, YHM warranties their SS .308 Phantom for use on barrels as short as 10.5". By my math, that barrel and chamber would have a combined volume of almost exactly 1 cubic inch. QuickLoad tells me to expect 20,626 psi at the muzzle, if I use a very light (110-gr) bullet and a SAAMI max pressure charge.

And 1 x 20,626 = (duh!) 20,626.

So I call that my "calculated ideal gas product," CIGP.

Suppose the intended host for the new Form1 suppressor is a 14" .30RAR. I get a chamber & bore volume of 1.22 cubic inches, and a peak muzzle pressure (also with a 110-gr bullet and a max pressure load) of 10,139 psi. So my .30RAR CIGP works like this:

1.22 x 10,139 = 12,369.58

Call it 12,370. So the .30RAR's CIGP is 40% less than the .308Win's.

The meat of my question is whether this is a valid means of determining that I can scale down the .308 suppressor by 40% (presuming the same design, proportions, and shell strength) so the theoretical .30RAR run through the 60% scale Form1 suppressor will have roughly the same peak SPL as the theoretical .308 through the full-scale suppressor, and with the same margin of safety against bursting.

Am I clueless or am I on to something?

[MCKNBRD]

I think you're overcomplicating it; I calculate the muzzle pressure in a similar way, but use that pressure (not gas 'volume') to calculate hoop stress for a cylinder...then I use the hoop stress value to determine wall thickness for a given cylinder diameter.

Taking YHM's can and reducing it 40% will make for an extremely poor performer. You're still going to need volume to absorb the blast and give it room to work, slow, and cool. Also remember that you're not just dealing with a gas; you're dealing with flow, pressure, particles, thermal fluctuations, and rapidly varying values for all of the above. Unfortunately, suppressor design is as much an art as it is a science.

My recommendation? If you like YHM's design, but want it smaller, figure out the wall thickness needed for the largest round you're likely to ever use the can on...and build one to handle that. I am much more likely to use a suppressor on a 5.56 rifle than a .30 cal...but I'm still building my centerfire can based on .308 specs.

Byrdman

[Bendersquint]

Suppressor designs are not scalable like you hupothesize.

Some companies will scale designs to fit their needs but it isnt based on anything besides not doing the research for the specific can they are designing.

All cartridges exhibit different characteristics that need to be accounted for. Just because the 30RAR is 40% the pressure of 308 doesnt mean a can 40% the size will give similar results.

Unforunately the only thing you are onto is a good mathematical discussion for math class worry about hoop stress as Byrdman says and build your core, if it doesnt work out submit another tax stamp and plan your next iteration over the next 9 months!

If suppressors were scalable then no company would be making bad cans and trust me there are a bunch of them out there!!!

[BungieCord]

Well, scratch that theory. [wads up large stacks of paper and tosses into round filing cabinet] Thank you for your expertise, gentlemen.

Hoop stress. Thanks twice, that was a term I needed to know.

I had considered there were properties that weren't scalable, like stuff that moves at a fixed rate (speed of sound, etc), but I figured the OP already had all the complications it needed. But it didn't matter in the end, because I obviously have wandered into the deep in of the pool.

It's not so much that I like the YHM design, it's that it was "professionally designed" and I happen to have one on hand to use as a model. What I want, in the end, is a suppressor for an AR (preferably up to a .30RAR) that doesn't so adversely affect the weapon's handling as the steel YHM does. Something lighter than 26 ounces, or shorter than 8.5 inches, or both. I wish now I'd sprung for the Ti version but it was a "political impulse buy," and the steel version was all they had in stock.

Byrdman, would you mind sharing your technique for calculating hoop stress? My primary concern is whether I can get by starting with store-bought Grade 9 Ti tubing. This suppressor also would see duty on a 5.56, which potentially could have a little higher pressure at the muzzle than the .30RAR, as much as 11,800 psi, according to QuickLoad.

[Bendersquint]

Well, scratch that theory. [wads up large stacks of paper and tosses into round filing cabinet] Thank you for your expertise, gentlemen.

Hoop stress. Thanks twice, that was a term I needed to know.

I had considered there were properties that weren't scalable, like stuff that moves at a fixed rate (speed of sound, etc), but I figured the OP already had all the complications it needed. But it didn't matter in the end, because I obviously have wandered into the deep in of the pool.

It's not so much that I like the YHM design, it's that it was "professionally designed" and I happen to have one on hand to use as a model. What I want, in the end, is a suppressor for an AR (preferably up to a .30RAR) that doesn't so adversely affect the weapon's handling as the steel YHM does. Something lighter than 26 ounces, or shorter than 8.5 inches, or both. I wish now I'd sprung for the Ti version but it was a "political impulse buy," and the steel version was all they had in stock.

Byrdman, would you mind sharing your technique for calculating hoop stress? My primary concern is whether I can get by starting with store-bought Grade 9 Ti tubing. This suppressor also would see duty on a 5.56, which potentially could have a little higher pressure at the muzzle than the .30RAR, as much as 11,800 psi, according to QuickLoad.

YHM's design is decades old.....they haven't done any updating in years. So yes it was "professionally"(if you want to call it that) designed decades ago......we have come a LONG way since then.

Yes store bought G9 Ti tubing will work fine so long as you determine the correct wall thickness.

[doubloon]

Excellent thread.

[BungieCord]

I just found the suppressor engineering thread, which I somehow had managed to overlook but found using a g**gle search. It not only answers my question about calculating hoop stress, it also should give me plenty to read and digest.

[Shift1]

I just found the suppressor engineering thread, which I somehow had managed to overlook but found using a g**gle search. It not only answers my question about calculating hoop stress, it also should give me plenty to read and digest.

That is an excellent post....we tried to make it a sticky but the board did not allow stickies at that time

[Homer]

G'Day Fella's,

Bungie Cord, I was just wondering how much smaller do you require a suppressor to be?

I'm currently manufacturing .223Rem/5.56mm suppressors/Cans that are only 4 1/2" (116mm) long , 1 1/2" (38mm) in diameter and 3/4 of a pound ish (360 grams) in weight. These dimensions are for the full size 7 baffle Can, I'm able to reduce to baffle count, which will reduce length and weight some more!

I also have a Proto-Type .308Win/7.62mm Can that is only 120 ish mm long and a .338 Lapua Magnum suppressor (a bit long to be called a Can), that is only 190mm or less than 8 inches long!

Unfortunately, I'm more at home in a workshop than I am on this Box of Trix, so I'm not sure how to post images of my products!
If one of you blokes would like to PM me, I'll give you my email address so you can post the images FYI???

Doh!
Homer

[Capt. Link.]

Sounds like you are producing a illegal item in your country.

[Bendersquint]

Sounds like you are producing a illegal item in your country.

+1

[BungieCord]

My problem with the .308 YHM I have is it makes a 16" AR too unwieldy. So it's not entirely a problem of weight, it also has something to do with the overall length (the "moment arm") with the suppressor affixed. Any reduction in weight or length would be a good thing but I'd be happier than a dead pig lying in the sun if I could get anywhere close to the 15 ounces (425g) YHM claims for their Ti .308 Phantom.

I've checked in QuickLoad and the pressure at the muzzle of the .30 RAR and a 7.62 Warsaw is lower than a 5.56 NATO, at least in any barrel lengths I ever might use, so I'm thinking a suppressor stressed for 5.56 but with a bore enlarged to accommodate a .311 bullet would be suitable for all three, which would make it awfully, awfully utilitarian. So the notion of a 12 ounce suppressor that would accommodate all three really gives me a woodie.

BTW, my YHM is a QD, and I like the QD function and plan to make this device QD. Although I have heard/read that AAC makes a better QD than YHM, which is something I'll have to look into, so I'm not necessarily married to YHM's QD. Anyway, I know the inclusion of a QD affects the suppressor design, so I thought I should get this into the conversation, in case it brushes against a topic where that difference would matter.

OT but I also was pondering a reflex design because there's a lot of real estate between the muzzle and the gas block on a carbine-length AR. Except I'm thinking a reflex design would be heavier than non-reflex with identical internal volumes, so I'd be trading added weight for less overall length. But that approach would not make the device (or the OAL of the weapon w/suppressor) any shorter unless I also move the blast baffle closer to the muzzle. And I've already decided not to mess with Inconel, so blast baffle lifespan is one of my chief worries.

[Homer]

G'Day Fella's,

Capt Link, no all of the work I do and production is legal, above board and with the total approval of the relevant Local and Federal authorities!

Bungie Cord, the weight of my Proto-Type .308/7.62mm "Can" mentioned above, is only 365 grams!
I still need to perform some additional function and abuse tests with this and the .338Lap Mag suppressor but I'm hopeful!!!

Doh!
Homer

[gunny50]

"Bendersquint"
Yes store bought G9 Ti tubing will work fine so long as you determine the correct wall thickness.[/quote]


Bender do you know if the Gemtech Quicksand 7.62 - Titanium silencer from Grade 9 tubing?

Gunny

Sorry guys deleted the Double post and typo ...

[Bendersquint]

"Bendersquint"
Yes store bought G9 Ti tubing will work fine so long as you determine the correct wall thickness.

Bender do you know if the Gemtech Quicksand 7.62 - Titanium silencer from Grade 9 tubing?

Gunny

Sorry guys deleted the Double post and typo ...[/quote]

Yes, its Grade9 tubing.

[gunny50]

Bender,

Thank you for the info.

Gunny

[wabbit]

Sounds like you are producing a illegal item in your country.

im in n.s.w.australia and we can own silencers just a bit of red tape