223 SS suppressor thickness safe limit

[vaeevictiss]

So i finally got my second form 1 can together. I made a .223 can out of 316SS for the tube and 416 for the internals.

The tube was .065 thickness. The whole can is 7.25" long and the blast chamber is 3" of that, with 5 60 degree baffles after with spacer in between. The can will be used on an ar15 with an 18" barrel.

after it was all together i wanted to take some material off the whole length and even it out and hide the welds. Well, i was dumb and the can got moved on the lathe so it got slightly uneven, there is now a slight ridge on one end and im worried i may just have to live with it. What im curious about is if the spacers inside account for any added strength, even if they are not welded together. They are just stacked in. the spacers, if i remember are somewhere from .030-.040 thick, ill just say .030 to be safe.

After turning some off the tube, im currently at 1.480 and the original ID was 1.370, so if im doing my math right, my outer tube should be at .055 thickness. Is is safe to go any further or should i just deal with it?

I have ran a couple mags thru it, one pretty fast, and im not seeing any signs of weakness or bulging. ive measured the od with a caliper before and after shooting and its not changed.

[Capt. Link.]

How thin you can go is partially up to how you constructed it.Without the baffles and spacers welded together no strength is gained.I would normally plug weld the baffles in place along with the end caps without spacers.You should use a burst calculator to figure out the limitations before you make another cut.

[vaeevictiss]

where would i find such a calculator?

[T-Rex]

Below

[vaeevictiss]

so how do i take other stuff into consideration like internal volume with baffles and how much pressure is created from each shot?

[Capt. Link.]

so how do i take other stuff into consideration like internal volume with baffles and how much pressure is created from each shot?

You don't take anything else into consideration other than the material used ,expansion chamber volume and the muzzle pressure from a 18.00" barrel plus any safety factor

Would someone please post the muzzle pressure for a 18.00" 5.56 barrel using 63,000 psi as chamber pressure.

[pdsmith505]

Quickload gives me about 11,000 PSI at the muzzle shooting a 77gr SMK on top of 24.3 gr of TAC loaded to 2.260" producing roughly 63,000 PSI in the chamber.

[vaeevictiss]

So how do i get the expansion chamber volume when you take into account that the muzzle brake goes into it?

Other than that, help me make sure I'm doing this right...

On the burst calculator i put

OD- 1.480
T- 0.550
S- 6503 (from here http://www.onlinemetals.com/merchant.cf ... &top_cat=1)
SF- 4 (the link above states to use a safety factor of 4)

This gives me a working pressure of 120.833psi and a burst pressure of 483.331psi. Did i do that correctly? Getting the boat chamber volume is going to be tricky as like i said the muzzle brake goes into it as well as the cone.

[T-Rex]

SAAMI lists 55k max psi.
Using this chart, let's call 18" to be 7k psi.


OD=1.48
T=.055
S=84000 from here
p=1560psi
Bursting=6243psi

Using the dimensions you provided, discounting muzzle brake volume, I get the following:
Chamber volume + bbl = .817in^3
Blast chamber volume = 4.42in^3
Blast chamber volume + total bbl = 5.237
5.237/.817=6.41
7000psI/6.41=1092

Lets be reasonable and say the inclusion of your muzzle brake gets you to 1300psi. You're well under your working pressure (with a very conservative SF of 4).

[vaeevictiss]

Man i wish i could math like that lol. That was my worst subject in school and go figure id take up a hobby it would help in.

So it's probably safe to take a little more off but how much is too much? Does that volume also take into account the ~.030 thick spacer in the blast chamber between the end cap and blast baffle (so 1.370 id plus the .030 spacer)?

Another question, where do things like the end cap welds and operating temps come in? These things as you know can really start cooking after a lot of fire. I would imagine the metal will get softer wouldn't it?


And how come 17" pressure is higher than 16"? That's strange.

[gunny50]

"T-Rex"

Lets do that calculation on an M2. with M33 ball.
chamber pressure - 54,800 psi (378 MPa)
barrel - 1143 mm

using 316 3" diameter seamless, what would be the minimal wall I would need for my M2 to have some quiet time.
Or should I go bigger and build a 4" diameter to cope with volume in FA?
Length 12" maybe 13"

I already designed and machined the QD brake that uses the same solution as the WW2 flash hider, just modernized it a bit

Want to build 2 cans 1 to work with the brake, 1 that works / connects just like the brake but is can only, no internal brake. 4 or 5" back over the barrel and 8 or 10" in front.

OD=3"
T=??
S=84000
p=?
Bursting=?

[Capt. Link.]

SAAMI lists .223 ammo at 55,000 psi NATO 5.56 is over 63,000 psi for ball.I always use the higher number as a safety factor plus a safety factor in all calculations.I don't have the mad skills of T-Rex but get by with doing the math.
TNX: pdsmith505 for your input I need that software!

Take this with much caution but you can use a very thin pressure tube.We had a member turn a tube to .005" on a .22LR suppressor before it failed.I have gone as low as .025 in grade 9 titanium with welded construction before it failed on a belt fed automatic using ball 5.56 ammo. These were done as experiments and are not safe for general use by the public.

I would examine your suppressor to determine how much needs to be removed then do the math before you cut.Rapid fire will lower the ability of the tube to resist rupture as will shorter than 18" barrels.

Best of luck stay on the safe side you'll live longer........time to stir the TNT pot on my old leaky gas stove...see ya poof.

CL

[vaeevictiss]

damn, .005 is insane. Thats a hell of a lathe (and machinist) to even get there. Thats not even two sheets of notebook paper thin.

Im looking and lets say i went down to .040 thickness. would i be good? I came across one of Ranb's old posts where he said;

"I used .035" 4130 for my last two 223 cans and they are doing fine. They have welded end caps and step cone or K baffles. I think 1/16th inch is plenty thick even for .308 and way too heavy for 223."

granted hes using a different material and im not sure how it compares to 316 nor how big his blast chamber is.

[T-Rex]

The "safest", and respectively practiced, thing to do is step the tube OD, as you pass the blast chamber + 1 baffle.
If you are using a spacer, in the blast chamber, the hoop stress of this should be taken into consideration, when factoring main tube thickness.

[vaeevictiss]

Actually the blast chamber spacer is part of the endcap. It was just a long machined and hollowed out piece. It goes to about the top of the blast baffle where there is just a short spacer to take up the rest of the gap.

and what is hoop stress?


pic below of blast chamber...best i could due to lighting but you can almost see the seam where the spacer part of the endcap meets the next spacer. To be specific, the muzzle brake actually was flush with the end of the spacer when connected so it was fully contained and takes all the brunt of the blast

[c5_nc]

If your at .055" I would stop there and live with it. I think the thinnest commercial can was .049", it was a reflex can so it has a sizeable blast chamber.

[vaeevictiss]

understandable. I should just deal with it.

But because that blast chamber spacer and end cap is all once piece, is there a chance that buys me any extra strength? Before i got it together i actually fired the gun with just the endcap on the muzzle because i have a stupid curiosity. It basically looked like one of those Noveske Pig brakes and was loud as hell but no damage to the endcap and it fit right back in the tube when i was done so no deformation either....granted everything was forced out the front. I would just assume since its all one piece that it would somehow strengthen that end of the can...then again im just hoping for something to work out here haha.

[KenHo]

Hoop Stress: https://en.wikipedia.org/wiki/Cylinder_stress has a good explanation. From what I read, in the thin walls used with suppressors this is a fairly small force.

BTW, you asked about how the thickness of the spacer in blast chamber would affect. "Ass-u-ming" the spacer OD is 1.370" with (worse case) .040" wall thickness would give an ID of 1.29"

new volume of blast chamber would be V=πr(sqr)h; or 3.14159*(1.29/2)sqr*3" or 3.92cu in.

New total volume (using same as T-Rex) 3.92 + .817 = 4.738

new ratio of brl to blast is 4.738/.817 = 5.99

using same muzzle psi: 7,000/5.99 = 1207 psi compared to 1092 without considering spacer thickness. 1207 psi is still a good safe working number.

This is my understanding how it all works - if not correct, someone PLEASE correct.

Ken H>