Building Suppressor for 18" .338LM

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dogtown
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Building Suppressor for 18" .338LM

Post by dogtown » Mon May 05, 2014 9:24 pm

Hey guys, I've had good luck with my .223 and .308 brake-attach suppressor builds and am now ready to move up to .338LM. I've got a few different barrels to work with from 18" to 34" and with the shortest one I reckon the pressures at the muzzle will be significantly stronger than anything I've dealt with so far. The plan is to scale up the .308 design to about 4.5cm (1.77") diameter and lengthen it to about 22cm (8.6"), build it out of 316 stainless and weld it all together in the hopes of creating something strong enough to handle the high pressure.

Is there anything obvious I'm missing? Any particular things to look for when making a strong enough suppressor?

Pman5KMO
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Re: Building Suppressor for 18" .338LM

Post by Pman5KMO » Tue May 06, 2014 3:05 am

18" .338 LM barrel seems like a waste of perfectly good powder and bullets to me..... you really do lose a lot with that barrel length.

22" would nearly offset weight wise, with what you could do with materials and improve velocity and range (obviously) a good deal. 18" you have comparable unburned powder as a 10.5" AR15 5.56 barrel. There is a very good reason you rarely see .338 LM barrels shorter than 24" let alone 22".... most are 26", and for VERY good reason.

So consider going longer barrel for a form 1, lest you discover tons of baffle erosion or want to have to deal with a 3# can that has 1/2" thick baffles to lengthen the life.

The only material I would use for that short a .338 barrel would be inconel.... would stand up better to the inevitable powder blasting.

The other issue with .338 is barrel thickness/weight. Medium taper (for a large bore) seems to be very common (or fluted) for .338 barrels for weight sake. Many cans for .338 are made to be lighter weight, and provide good repeatable accuracy and minimal POI shift.

Pressure wise you are looking at about 300 winmag pressure ranges.... but an 18" .338 LM would be like having a 16" 300 winmag.....
Suppressors cost less than hearing aids..

dogtown
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Re: Building Suppressor for 18" .338LM

Post by dogtown » Tue May 06, 2014 3:23 am

I'm in NZ so I don't need permission to build a suppressor nor am I prevented from modifying it ;)

It's on a switch barrel system (SRS) that I originally ran a 26" barrel on and am now working on a longer 34" barrel for shooting beyond 2000m. The short 18" barrel is very handy for a number of applications and I find that it's the barrel I tend to rely on inside of 1400m. I just want to suppress these barrels now but every time I think about the pressure at the muzzle on that short barrel it makes me second guess things.

I would think Inconel would make more sense for sustained firing vs bolt gun shooting as its main advantage is heat resistance, no? I'd consider going the titanium route but the guy who builds my parts isn't too keen on that material.

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Shift1
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Re: Building Suppressor for 18" .338LM

Post by Shift1 » Wed May 07, 2014 8:39 pm

Muzzle pressure should definitely be considered. I had the same issues and concerns with a 16.5 inch .308.....was looking as something like 12,000 psi at the muzzle. 338 Lapua at 18 inches.....definitely need to at least think about that.
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dogtown
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Re: Building Suppressor for 18" .338LM

Post by dogtown » Thu May 08, 2014 8:00 pm

So with such high pressures in mind, what should I consider doing differently? Weld baffle stack and end caps? Thicker tube?

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Shift1
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Re: Building Suppressor for 18" .338LM

Post by Shift1 » Sat May 10, 2014 9:34 am

I would suggest it should be a welded design. You will also need to be aware of baffle stack crush and erosion...there is the initial radial expansion on the tube then the forward push on the baffles. The shorter barrel and large powder volume will contribute to a somewhat accelerated erosion cycle. There will be products of combustion passing through the baffles....
"The Constitution shall never be construed to prevent the people of the United States who are peaceable citizens from keeping their own arms."- Samuel Adams
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dogtown
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Re: Building Suppressor for 18" .338LM

Post by dogtown » Sat May 10, 2014 8:58 pm

Just the kind of info I was wanting - thanks!

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gunny50
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Re: Building Suppressor for 18" .338LM

Post by gunny50 » Mon May 12, 2014 5:09 am

Shift1 wrote:I would suggest it should be a welded design. You will also need to be aware of baffle stack crush and erosion...there is the initial radial expansion on the tube then the forward push on the baffles. The shorter barrel and large powder volume will contribute to a somewhat accelerated erosion cycle. There will be products of combustion passing through the baffles....

I use a welded core and welded tube front and rear, not only a welded end-cap, spot welds to all baffles at critical points as well.
This is a Ti can on a 20" 338 same design on a 12" 308 semi.

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domestique
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Re: Building Suppressor for 18" .338LM

Post by domestique » Fri May 16, 2014 8:02 pm

A guy over at Snipershide blew up his Thunderbeast 338 can a couple months ago on a 16" DTA SRS in 338 Lapua. The end cask blew out the front.

I believe the shortest TB recommended was at 20" and the guy said he would no longer be going shorter then 22" to be on the safe side. I believe the pressure of a 16" 338 is the same as a 8" 308.

O, numerous people looked for the can innards and to my knowledge they are still MIA.

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Capt. Link.
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Re: Building Suppressor for 18" .338LM

Post by Capt. Link. » Fri May 16, 2014 9:11 pm

You will need to build that suppressor like a tank.A collection of unburnt magnum powder in the suppressor tube will create a magnificent plume of bright light as it detonates.It should be DE-bomb!
The only reason after 243 years the government now wants to disarm you is they intend to do something you would shoot them for!

dogtown
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Re: Building Suppressor for 18" .338LM

Post by dogtown » Fri May 16, 2014 9:36 pm

domestique wrote:A guy over at Snipershide blew up his Thunderbeast 338 can a couple months ago on a 16" DTA SRS in 338 Lapua. The end cask blew out the front.
Yup, I know that guy and sure enough the can wasn't rated for such a short .338LM. DTA's own .338 can is rated for their short 18" barrel, so it's not like it's impossible, but since I moved to NZ there's no chance of me getting one so I might as well build.

A tank indeed! I'm scaling up my .308 design, padding the thickness on a number of parameters and welding it throughout. Sadly, I'm expecting this sucker to weigh quite a bit.

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