I need help with a form 1 question on the blast chamber

[NS0S]

I have read and read and read. Reading can only do so much if you don't know what to look for or what it means.

For starters, how do I determine the pressure rating for grade 9 titanium that is .070" thick? I read linked sources but it gave me nothing I understood. This site supposedly says the measurements I need to know. I don't see them. http://www.finetubes.co.uk/products/spe ... r.-3.7194/

I understand that 5.56mm ammo has a blast pressure of 55,000 psi. I read from a study Gemtech did that the blast pressure of a 10.5" barrel is 11,500 but I don't understand why. I calculated that there should be about 7.25 cubic inches of volume in the barrel. I would assume that something that is 55,000 psi would become 7.25 times less pressurized if that much space was added. So, why isn't the pressure 7500 psi?

Basically I am trying to figure out what would be a safe size for a blast chamber. I read that a 1.5 times safety factor is a good place to be. I can calculate the length of the spacer if I knew what the volume needed to be. I know the material. I would assume that 1.5 times would be more than safe. Especially taking into account that there is a titanium spacer resting against the edge of the tube.

I don't mind figuring it out on my own. I just don't understand the material to determine what I need to know.

So, in short:
At what pressure does grade 9 titanium that is .070" thick start to go haywire?
What should the volume of the first chamber be to bring it to a safe level knowing that the pressure at the tip of the barrel will be 11,500 psi?
How did you come up with those numbers?

I really appreciate the help. I swear I tried to figure this out on my own.

[ECCO Machine]

OK, one, the internal volume of a 10.5" AR barrel is nowhere near 7.25 cubic inches. It's about 0.4 CI. Secondly, gas pressure attenuation with increased volume (Boyle's law) isn't perfectly linear.

Now, as for figuring the strength of your material and the strength required, that's even more math. You have to multiply the pressure by the area it's acting upon, relate that to tensile yield strength times area affected. But you can't just take the muzzle exit pressure figure, because as soon as it uncorks in a 1.35" ID x 2" long blast chamber, you're going from .4 CI to a combined barrel & blast chamber volume of about 3.25 CI, a massive increase that will bring your pressure down more into the 1,200-1,500 PSI range.

You also need to know what temper your Ti has to properly figure it's strength.

Now, all that said, .070" wall gr.9 annealed is more than strong enough for 5.56 SBR. I've run half that thickness with full auto fire from a 13" .308, and the can was already ~1,600°F when I cut it loose.

[T-Rex]

Wall thickness, alone, won't get you anywhere. You'll need to input the tube/vessel OD. And, as Ecco stated, the instant the bore gas enters the BC it's pressure drop will be huge. Another thing to consider is that a suppressor body should never be a sealed vessel. It's the elevated temperature and repeated impulses that should be weighed.

There is an easy to use burst calculator, in my sig line, below.

[NS0S]

Thanks for the help so far. I have no idea why I jacked up the volume calculation so bad. I was pretty tired last night. Sorry about that.

The tube OD is 1.5 inches. Specifically the titanium is ALLOY TI 3AI/2.5V. I have been looking at the burst calculator but I don't understand some of the information needed for it. I don't know what number to use for the Allowable Stress(S).

[SuthDet]

You have 3 options:
Tensile strength, the point it will blow up
Yeild strength, the point it will permanently deform, normally considered to be the failure point
Or some lower value based on your safety factor and your confidence in your numbers.

I'd suggest using the 3rd option.

[ECCO Machine]

You have 3 options:
Tensile strength, the point it will blow up
Yeild strength, the point it will permanently deform, normally considered to be the failure point
Or some lower value based on your safety factor and your confidence in your numbers.

I'd suggest using the 3rd option.

Pretty much.

Allowable margins depend on many things, but it'd be pretty unusual IME to see a material specified that doesn't have a yield strength at least 20% higher than the maximum load the material will bear.

As I mentioned above, though, you don't really need to do any of this math unless you're trying to go thinner that was has been previously engineered and proven to work. 1.5" OD .070" wall gr 9, even annealed, gives you well more than a 100% margin with 5.56 SBR.

[NS0S]

You have 3 options:
Tensile strength, the point it will blow up
Yeild strength, the point it will permanently deform, normally considered to be the failure point
Or some lower value based on your safety factor and your confidence in your numbers.

I'd suggest using the 3rd option.

I understand what the value stands for. That wasn't my question. I don't understand what numbers to use for it. I don't know what the numerical values are. What number is the yield or tensile stregth for the material I specified.

And ECCO, then what would be a preferable space to use. I don't want a ton of blowback and I don't want it so big it pops everytime. I have a 2" spacer. The muzzle will be in the tube so it will use a little volume. Should I just run it like that and call it good?

It just seems there is a lot of emphasis on the blast chamber. I was worried I might make a mini pipe bomb of it was too small. I appreciate the help so far.

I have been looking for a source of a titanium impeller or compressor wheel that is very small. I thought it might be something neat to try. Everyone says you want the gas to stay in the tube a long time. The longest route of a circle is around the edge. I might scrap that idea and just go conventional.

Here is a pic of what I mean. Not exactly like this but similar. More of an impeller.

http://shopping.kinugawaturbo.com/image ... /nn.18.JPG

[SuthDet]

http://lmgtfy.com/?q=Material+propertie ... 9+titanium

[NS0S]

http://lmgtfy.com/?q=Material+propertie ... 9+titanium

Can the mods ban this guy? I am past googling something that I don't understand. I don't appreciate someone being a dick. I try my hardest daily to help people. If you had a question about radios, antenna, emergency medicine, or firefighting I would love to help. I am sorry I don't understand yield and tensile strength. I don't need a troll jacking with me when I am genuinely seeking guidance. I can easily read the properties of something. But, the fact is what I am reading and the numbers I have seen are vastly different and I don't understand how they correlate.

I have read the properties. It doesnt mean anything. If it said the yield strength is 90ksi and I am looking at pressures in the thousands there is something missing I don't understand. Nothing I have read says that a tube this thick with a diameter this large has a yield strength of this. If I knew how to understand the material I was reading I wouldn't ask for help. I have already read what the properties are.

[ECCO Machine]

And ECCO, then what would be a preferable space to use. I don't want a ton of blowback and I don't want it so big it pops everytime. I have a 2" spacer. The muzzle will be in the tube so it will use a little volume. Should I just run it like that and call it good?

It just seems there is a lot of emphasis on the blast chamber. I was worried I might make a mini pipe bomb of it was too small. I appreciate the help so far.

The size of the blast chamber won't have much impact on your blowback one way or the other, not enough volume even with a large one to be a major factor there.

In general, subsonic or low pressure rounds don't really need much of a blast chamber, and a larger one with those rounds will lend to more first (and maybe 2nd, 3rd, 5th) round pop. HIgh pressure super sonic rounds do benefit from it, it helps deal with the initial large, fast pressure bubble at uncorking that wants to go straight through the bore with the faster bullet. A good brake design within the chamber will also help with this.

There is no "ideal" size of blast chamber, highly variable not only by the cartridge you intend to suppress, but the overall suppressor design. That said, I don't know what your mount looks like, but assuming it's thickness is similar to the muzzle threads at 1/2" to 5/8", a 2" spacer running 60° cones isn't going to leave you much over an inch from muzzle to blast baffle. I'd go with enough spacer that you have at least 1.5" from muzzle to tip of blast baffle cone. If the can is going to be 8"+, go 2" to 2.5".

I have read the properties. It doesnt mean anything. If it said the yield strength is 90ksi and I am looking at pressures in the thousands there is something missing I don't understand. Nothing I have read says that a tube this thick with a diameter this large has a yield strength of this. If I knew how to understand the material I was reading I wouldn't ask for help. I have already read what the properties are.

That's what the burst calculator does for you.

You have to think of the material cross sectionally, it's thickness. Annealed gr 9 Ti has a TYS of 72 KSI. To calculate the tube yield strength of a 1.5" OD .070" wall pipe, its 2*(TYS)*(wall thickness)/OD. So 2*72,000*.07/1.5. The answer is 6,720 PSI. To figure your safety factor, just further divide. 30% safety margin is 6,720/1.3=5170 PSI

Your burst pressure is calculated the same way, just plug in UTS instead of TYS. gr. 9 annealed is 90 KSI UTS. 2*90,000*.07/1.5=8,400 PSI burst pressure

Even if it were a closed system, an exit pressure of 10,500 PSI from the .4 CI barrel volume would drop to about 1,250 PSI in a 3 CI blast chamber, less than 1/4 of your working pressure with safety margin. And it's not a closed system, so the actual pressure is somewhat lower (very difficult to calculate, really have to physically measure it for a given can).

[T-Rex]

I recommended an easy to use calculator. One which you need not understand much of anything. It explains the necessary input parameters. Did you give it a try?

[NS0S]

I recommended an easy to use calculator. One which you need not understand much of anything. It explains the necessary input parameters. Did you give it a try?

I tried. My issue was I didn't understand what one of the inputs should be. The calculator has an input that is like 30,000 and all the stuff I saw for yield and tensile strength on the metal properties was 90-120 so I thought something must be off. I did not understand what it was wanting to put in that field.

I also did understand the properties because the description appears incomplete. If someone says something has a 90ksi yield rate what is that based off. I have no idea how think the metal they were testing was. I am guessing their is an industry standard thickness that these test are done at. I did not know what they were so I did not understand the information that was posted. It is just showing the grade of metal. Not how the metal is formed or used or how thick it is.

I can completely understand the calculators. I just didn't understand the metal properties from the manufacture.

AND THANKS ECCO. I think I figured out my issue. It was the KSI thing. I thought is was measuring pressure in the metric system. I have never heard someone call something a KILO Pound. I didn't realize 90ksi was 90,000psi. Now it all makes more sense. Maybe if they called is kpsi I would of figured it out. We use high pressure stuff every day at work. I wear an air bottle all the time. I worked with hydraulics on helicopters in that Army. I have never heard of ksi. I was thinking a kilo is 2.2 pounds so something is off.

[ECCO Machine]

I tried. My issue was I didn't understand what one of the inputs should be. The calculator has an input that is like 30,000 and all the stuff I saw for yield and tensile strength on the metal properties was 90-120 so I thought something must be off. I did not understand what it was wanting to put in that field.

You just click on those boxes and overwrite, put in the values for the material you're dealing with.

I also did understand the properties because the description appears incomplete. If someone says something has a 90ksi yield rate what is that based off. I have no idea how think the metal they were testing was. I am guessing their is an industry standard thickness that these test are done at. I did not know what they were so I did not understand the information that was posted. It is just showing the grade of metal. Not how the metal is formed or used or how thick it is.

I can completely understand the calculators. I just didn't understand the metal properties from the manufacture.

The measurements are based on PSI as the unit implies; one square inch of a material with a 90,000 PSI TYS rating can suspend 90,000 pounds before stretching. Compressive yield strength is how much weight 1 sq in can bear before deforming.

I think I figured out my issue. It was the KSI thing. I thought is was measuring pressure in the metric system. I have never heard someone call something a KILO Pound. I didn't realize 90ksi was 90,000psi. Now it all makes more sense. Maybe if they called is kpsi I would of figured it out.

SI (Metric) will be Pascals/Kilopascals: Pa, kPa. A pascal is one Newton per square meter.

Sometimes you'll see KPSI, but common imperial ANSI/ASME denotation dealing with material mechanical properties that will be in the tens or hundreds of thousands is KSI, which actually does stand for kilopound per square inch.

[NS0S]

Thanks again ECCO. With the correct numbers it all makes a lot of sense.

I have another simple question. Anyone who reads this can chime in. Anyone know a source on deep mounts for a D Cell tube? The thread pattern needs to be 1.4375X20 which is the standard mag light thread. Liberty sells them for my Mystic X and Centurion. He is a link to what they look like.

https://libertycans.net/product/fixed-barrel-adapter/

I would figure as popular as the Form 1 market is someone would make them. I am surprised SD Tactical doesn't. I still need to buy another Liberty one because the Mystic X only comes with a flush 1/2 by 28. The Mystic X is only rated for a 16 inch barrel with the flush mount. But damn are those things expensive. $95 and it doesn't include shipping.

[NS0S]

Thanks again ECCO. With the correct numbers it all makes a lot of sense.

I have another simple question. Anyone who reads this can chime in. Anyone know a source on deep mounts for a D Cell tube? The thread pattern needs to be 1.4375X20 which is the standard mag light thread. Liberty sells them for my Mystic X and Centurion. He is a link to what they look like.

https://libertycans.net/product/fixed-barrel-adapter/

I would figure as popular as the Form 1 market is someone would make them. I am surprised SD Tactical doesn't. I still need to buy another Liberty one because the Mystic X only comes with a flush 1/2 by 28. The Mystic X is only rated for a 16 inch barrel with the flush mount. But damn are those things expensive. $95 and it doesn't include shipping.

[garredondojr]

I think you'll find that most of us here build our own. The maglight (b,c,d) tubes aren't very common. the 24 tpi options from diversified machine and the like are a better suited to most builds.

I could be wrong but the main reason you won't see direct thread adapters like that here is why not run a longer tube than what amounts to a flash can addition? I can see it on a modular can but depending on what your working on its going to add alot to the blast chamber which can result in more FRP.

On a side note. depending on how your building your suppressor. as a Form 1 builder if you used that style mount as an endcap it would likely be deemed a "suppressor part" so it would be your only form of mounting as if you had other mounts they too would be deemed suppressor parts and each part is considered a suppressor if it cannot be configured as 1 unit which can land you in alot of hot water.

DM sells blast shields which is the same idea but uses griffin muzzle devices (website says cherry bomb options are in the works) https://diversifiedmachine.us/product/g ... st-shield/

But again this would be considered a endcap which would be a suppressor part unless you made or have made a endcap that goes to your tube size then to the thread on the blast shield. you can accomplish the same thing (or better in my opinion) by just running a longer tube with what ever mounting option you prefer.

[NS0S]

It is just the mounting style I want to use. No special reason.

It would be nice just to make a can from scratch. But, (A) I am not a machinist, (B) I don't have any machinist tools, and (C) kids cost too damn much to go buy the tools. I will hopefully have a nice fun workshop in 8 years. My youngest kid is in the 8th grade.

In the mean time I can do fun little things like this once in a while. I will be buying a new roof on my house and driveway before I go buy a lathe. My career field is firefighting. I was a helicopter mechanic in the military and I worked at Freightliner in high school. To this day I can proudly say I have never had a car/motorcycle/truck fixed at a dealer unless it was under warranty(with the exception of body work). I thing I have the aptitude for it. I just don't have the space, equipment, or time for that matter. It would be fun to try though. I really would like to make a firearm from scratch one day. That would be a lot of fun.

[garredondojr]

It is just the mounting style I want to use. No special reason.

It would be nice just to make a can from scratch. But, (A) I am not a machinist, (B) I don't have any machinist tools, and (C) kids cost too damn much to go buy the tools. I will hopefully have a nice fun workshop in 8 years. My youngest kid is in the 8th grade.

I really would like to make a firearm from scratch one day. That would be a lot of fun.

I hear that! I have 5 little critters myself however mine are still little youngest being 2.5

Nothing wrong with how you want it, but there are more efficient ways about it. be sure if you do run said mounting device that you add that to the length of the suppressor when filing your form 1 (safer to overestimate than under. they don't frown upon slightly shorter but longer they do. so I've heard at least) you can always send a letter stating an adjustment (caliber, length, ect..)

One thing I would recommend however is to consider a muzzle device attachment. it will greatly open mounting options (griffin and q's cherry bomb being some of the more popular options out there for the F1 builders) you could buy direct thread or minimalist mounts and screw them into the can and use it as a direct thread can with said device in it, then if you later down the road want to put it on a different host that has special threads you just buy said muzzle device. It also gives you more mounting options. ie. say you want less of the can length added to the muzzle you could run a OTB (over the barrel) mount and most importantly having a brake helps lessen wear on your blast baffle as it acts as a sacrificial blast baffle but is legal to replace as it's not a suppressor part.

I have plans to do a scratch build one day myself. looking forward to it.

[NS0S]

I like the OTB idea a lot. I already did my Form 1 and I made it a little long just to be safe. I just don't know how I would go about doing it with the parts I have already purchased. It would me a pain in the behind. Plus, it won't work with the hand guard on that firearm. My next suppressor will be a 22 can but I will probably buy a commercial one when the ATF opens the eForm 4s in a next month or in January. I really want an integrated 10/22 barrel silencer. But, I also really want a little 22 pistol so I will probably get something I can use on both.

This is just a fun suppressor to get my feet wet. While I was off work over the summer I designed a bunch of exotic monocore designs and baffle systems. I hope to try them out sometime but I have other stuff on my plate now. I need to finish some stuff for scouts too.

[SuthDet]

http://lmgtfy.com/?q=Material+propertie ... 9+titanium

Can the mods ban this guy? I am past googling something that I don't understand. I don't appreciate someone being a dick. I try my hardest daily to help people. If you had a question about radios, antenna, emergency medicine, or firefighting I would love to help. I am sorry I don't understand yield and tensile strength. I don't need a troll jacking with me when I am genuinely seeking guidance. I can easily read the properties of something. But, the fact is what I am reading and the numbers I have seen are vastly different and I don't understand how they correlate.

I have read the properties. It doesnt mean anything. If it said the yield strength is 90ksi and I am looking at pressures in the thousands there is something missing I don't understand. Nothing I have read says that a tube this thick with a diameter this large has a yield strength of this. If I knew how to understand the material I was reading I wouldn't ask for help. I have already read what the properties are.

Sorry to get off on the wrong foot. Being abrasive is kind of a hobby, so I can get carried away.

How you were wording your questions, it seemed like that was what you were looking for, though I could have replied more kindly.

My reasoning for being short and to the point, instead of walking you through every single step, is to prevent someone from hurting themselves. If you're going to use a calculator like that to design and manufacture something, you really need to understand what each value is. If someone just provides a value, it might work for you, then Joe average finds the thread, and uses the same value for a different setup, and his can blows up.

I strongly recommend reading up on engineering stress, particularly stress related to pressure vessels. This would really help you understand the numbers people are giving you as well as what that calculator is doing.