300 series stainless as tube material

[Will_M]

I'm considering doing a Form 1 can using 316 stainless with 1.5" OD and 0.065" wall thickness. I found an article by Dr. Dater of Gemtech. He has some pressure data from testing he performed.

http://sadefensejournal.com/wp/?p=573

Assuming the data is correct, and the blast chamber pressure is roughly 3,000 psi on a 10" barrel 5.56mm rifle, how are companies like SilencerCo able to use 316SS as a tube material?

My calculations:

Hoop stress = (blast chamber pressure * radius of chamber) / wall thickness.

Hoop stress = (3000psi*0.685inch)/(0.065") = 31,615psi.

The yield stress of 316SS is only 30,000 psi according to my sources online. How are they able to rate their cans for full auto SBR use? Do they use a thicker wall? Should I consider a different material for my tube?

[RJT]

Tube looks like an outer layer in this cutaway, that's how they are getting away with it most likely.

[Will_M]

Looking at my Specwar that's what I figured. So the blast chamber is actually Stellite? The tube isn't taking the pressure?

[Bendersquint]

Looking at my Specwar that's what I figured. So the blast chamber is actually Stellite? The tube isn't taking the pressure?

Blast chamber is not stellite, the baffles are stellite.

[Will_M]

Looking at my Specwar that's what I figured. So the blast chamber is actually Stellite? The tube isn't taking the pressure?

Blast chamber is not stellite, the baffles are stellite.

So the 316SS tube is able to contain that pressure? How can I be sure my 316SS tube can take the pressure from a 10" barrel? Is 0.065" thick seamless tubing strong enough? I understand the size of the blast chamber is extremely important, but I based my calculations off of the numbers from Dr. Dater's test.

[Dr.K]

Looking at my Specwar that's what I figured. So the blast chamber is actually Stellite? The tube isn't taking the pressure?

Blast chamber is not stellite, the baffles are stellite.

So the 316SS tube is able to contain that pressure? How can I be sure my 316SS tube can take the pressure from a 10" barrel? Is 0.065" thick seamless tubing strong enough? I understand the size of the blast chamber is extremely important, but I based my calculations off of the numbers from Dr. Dater's test.

does your design incorporate a spacer for the blast chamber? if so I would not hesitate to make it .065".

if your wall thickness is the only thing containing the blast, you may consider going thicker. I have one that is .100" 316L SS with no spacer. But, I've only ran it on a 16 inch barrel.....no issues.

Welcome to the form1 addiction!

[Will_M]

does your design incorporate a spacer for the blast chamber? if so I would not hesitate to make it .065".

if your wall thickness is the only thing containing the blast, you may consider going thicker. I have one that is .100" 316L SS with no spacer. But, I've only ran it on a 16 inch barrel.....no issues.

Welcome to the form1 addiction!

At this point I hadn't considered a spacer, but that could definitely be arranged. Would I be correct in assuming that the spacer would then become the pressure vessel for the blast chamber and would have to be spec'd accordingly?

[Capt. Link.]

At this point I hadn't considered a spacer, but that could definitely be arranged. Would I be correct in assuming that the spacer would then become the pressure vessel for the blast chamber and would have to be spec'd accordingly?

Sir .065 will be enough to contain the pressure.A spacer in the blast chamber will not increase burst pressure but will help with erosion from a short barrel.You should make the first several baffles from inconel for the same reason.A short barreled 5.56 will eat baffles so you may wish to build this as a take apart unit so it may be serviced from time to time.

[gunny50]

At this point I hadn't considered a spacer, but that could definitely be arranged. Would I be correct in assuming that the spacer would then become the pressure vessel for the blast chamber and would have to be spec'd accordingly?

Sir .065 will be enough to contain the pressure.A spacer in the blast chamber will not increase burst pressure but will help with erosion from a short barrel.You should make the first several baffles from inconel for the same reason.A short barreled 5.56 will eat baffles so you may wish to build this as a take apart unit so it may be serviced from time to time.

I do have one Question in this case, is it not so that when the core is fully welded en the outer tube is a press / shrink fit that both wall thicknesses can be combined as a total wall thickness?
As gas can not go in-between the 2?

I do see that when one uses a separate spacer that when the gas can flow between baffles and tube the pressure can do its work on the outer tube.
And on really short 556 a take apart can would be a good option.

Gunny

[Capt. Link.]

At this point I hadn't considered a spacer, but that could definitely be arranged. Would I be correct in assuming that the spacer would then become the pressure vessel for the blast chamber and would have to be spec'd accordingly?

Sir .065 will be enough to contain the pressure.A spacer in the blast chamber will not increase burst pressure but will help with erosion from a short barrel.You should make the first several baffles from inconel for the same reason.A short barreled 5.56 will eat baffles so you may wish to build this as a take apart unit so it may be serviced from time to time.

I do have one Question in this case, is it not so that when the core is fully welded en the outer tube is a press / shrink fit that both wall thicknesses can be combined as a total wall thickness?
As gas can not go in-between the 2?

I do see that when one uses a separate spacer that when the gas can flow between baffles and tube the pressure can do its work on the outer tube.
And on really short 556 a take apart can would be a good option.

Gunny

I think from a engineering point you would have a reinforced chamber and not a combined thickness chamber I could be wrong.

[Dr.K]

I think from a engineering point you would have a reinforced chamber and not a combined thickness chamber I could be wrong.

I'm no engineer, but I definitely fit deeply inside the realm of "mad scientist".

If the spacer is snugly fit between the blast baffle, and the rear cap, and is a solid piece...and fits within 5 thou of the ID of the tube.

If it was suddenly put under a high pressure load, and started to expand outward as it pushed into the outer tube, it would certainly push back and support the spacer thereby increasing the load it would be capable of handling.

It's not different that lighting off a cartridge in a firearm chamber, the brass expands, fills the chamber, but the chamber keeps the brass from rupturing (in most cases) because it supports it.

I see no difference here in our silencer example.

[Historian]

I think from a engineering point you would have a reinforced chamber and not a combined thickness chamber I could be wrong.

I'm no engineer, but I definitely fit deeply inside the realm of "mad scientist".

If the spacer is snugly fit between the blast baffle, and the rear cap, and is a solid piece...and fits within 5 thou of the ID of the tube.

If it was suddenly put under a high pressure load, and started to expand outward as it pushed into the outer tube, it would certainly push back and support the spacer thereby increasing the load it would be capable of handling.

It's not different that lighting off a cartridge in a firearm chamber, the brass expands, fills the chamber, but the chamber keeps the brass from rupturing (in most cases) because it supports it.

I see no difference here in our silencer example.

+1

Excellent observation and extrapolation.

E.g., Hard/soft ... Katana

Best.