308/7.62 Design review

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pdx Gun Mechanic
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308/7.62 Design review

Post by pdx Gun Mechanic » Tue Apr 15, 2014 6:07 pm

Hello All,

I’ve been a long time lurker. Reading, studying, taking notes and learning a lot from all of you. Thank you for this sight!

Will you please critique my 308 design?

The host is a Remington 700 .308 AAC-SD with a 20” threaded 1/10 barrel.

My goals for this build in order of importance: 1. Accuracy/minimal shift in POI 2. sound suppression 3. Light weight

Materials: Tube: Ti grade 9. All other components 316 stainless steel. Debating on if the extra cost justifies making the entire suppressor out of Ti. I think it would be around $400 more.

Thank you,

Gun Mechanic

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Dr.K
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Re: 308/7.62 Design review

Post by Dr.K » Tue Apr 15, 2014 6:47 pm

You will have a pretty good performer there.

I suggest you round off the sharp corners on the bottom of the cones. Also, I would clip them.

Welcome.
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Re: 308/7.62 Design review

Post by pdx Gun Mechanic » Tue Apr 15, 2014 7:17 pm

Thanks Kyle! As you can probably tell, some of my inspiration came from your posts/build. How did your 308 build turn out? I never could find your post on the end product.

What do you mean by clip?

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Re: 308/7.62 Design review

Post by Dr.K » Tue Apr 15, 2014 7:41 pm

pdx Gun Mechanic wrote:Thanks Kyle! As you can probably tell, some of my inspiration came from your posts/build. How did your 308 build turn out? I never could find your post on the end product.

What do you mean by clip?
Little half moon shapes cut out of the entry holes of the baffles. It causes cross jets of gas to push things off center of the bore line, and hold the stuff inside the can just a wee bit longer.

It makes enough difference on centerfire rifle that I could tell a difference (just barely) with my ears, which tells me it likely reduces report by 5-6 decibels. The SDN6, Spcewar, and the Saker all have this feature, so I took their word for it. :lol:

Like this.
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CMV
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Re: 308/7.62 Design review

Post by CMV » Tue Apr 15, 2014 8:06 pm

Around $200/ft more for Gr5 Ti vs 316 1.5" bar stock if you're looking at online metals so your estimate of $400 is probably pretty close. Titanium Joe has better prices for that material. But you could just do the cones w/o attached spacers out of Ti and use tube for spacers. That would use a lot less bar stock & keep the Ti cost lower if you wish.
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Re: 308/7.62 Design review

Post by whiterussian1974 » Tue Apr 15, 2014 10:19 pm

Dr.K wrote:I suggest you round off the sharp corners on the bottom of the cones. Also, I would clip them.
DrK, which part of the Cone Mouth would you round? Wouldn't gas erosion smooth any sharp edges around mouth and carbon coat edges around base?

Or did you mean cone base needs attention?
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Re: 308/7.62 Design review

Post by 57fairlane » Tue Apr 15, 2014 10:26 pm

are you planning on welding this together?

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Dr.K
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Re: 308/7.62 Design review

Post by Dr.K » Wed Apr 16, 2014 12:56 am

whiterussian1974 wrote:
Dr.K wrote:I suggest you round off the sharp corners on the bottom of the cones. Also, I would clip them.
DrK, which part of the Cone Mouth would you round? Wouldn't gas erosion smooth any sharp edges around mouth and carbon coat edges around base?

Or did you mean cone base needs attention?
With my first few cans I left a sharp edge at the bore line. Accuracy was fantastic then after several hundred rounds I seemed to be getting contact and accuracy degraded terribly. Upon inspection I noticed little spikey fingers growing inward toward the center axis. They were contacting the bullet slightly.

Material was 316L stainless, and after putting a nice smooth polished rouned edge on each baffle, accuracy was restored, and I have had no issues since, and have fired several hundred rounds.

Now when I see sharp angles on 316 I warn of this phenomenon.
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whiterussian1974
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Re: 308/7.62 Design review

Post by whiterussian1974 » Wed Apr 16, 2014 11:08 am

Dr.K wrote:Upon inspection I noticed little spikey fingers growing inward toward the center axis. They were contacting the bullet slightly.

Material was 316L stainless, and after putting a nice smooth polished rouned edge on each baffle, accuracy was restored, and I have had no issues since, and have fired several hundred rounds.
Maybe it's caused by one of the constituent materials in the alloy? https://en.wikipedia.org/wiki/Whisker_( ... #Mechanism
I was aware of Whiskering in electronics. Perhaps in other environments and apps too?
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Re: 308/7.62 Design review

Post by DanielWilson » Wed Apr 16, 2014 2:51 pm

Fascinating! I never heard of whiskering. From the article:
The mechanism behind metal whisker growth is not well understood, but seems to be encouraged by compressive mechanical stresses including:

[*]residual stresses caused by electroplating,
[*]mechanically-induced stresses,
[*]stresses induced by diffusion of different metals, and
[*]thermally-induced stresses.
Some of that could happen inside a suppressor, I suspect!

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whiterussian1974
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Re: 308/7.62 Design review

Post by whiterussian1974 » Wed Apr 16, 2014 3:02 pm

DanielWilson wrote:Fascinating! I never heard of whiskering. From the article:
The mechanism behind metal whisker growth is not well understood, but seems to be encouraged by compressive mechanical stresses including:

[*]residual stresses caused by electroplating,
[*]mechanically-induced stresses,
[*]stresses induced by diffusion of different metals, and
[*]thermally-induced stresses.
Some of that could happen inside a suppressor, I suspect!
The last 3 definitely. It's good to know that DrK has had great results w rounding the sharp edges. That and adding lead or Nickel-plating are 2 of the Mitigation Strategies suggested.
I prefer DrK's solution. ;)
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pdx Gun Mechanic
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Re: 308/7.62 Design review

Post by pdx Gun Mechanic » Wed Apr 16, 2014 4:28 pm

Dr.K wrote:
pdx Gun Mechanic wrote:Thanks Kyle! As you can probably tell, some of my inspiration came from your posts/build. How did your 308 build turn out? I never could find your post on the end product.

What do you mean by clip?
Little half moon shapes cut out of the entry holes of the baffles. It causes cross jets of gas to push things off center of the bore line, and hold the stuff inside the can just a wee bit longer.

It makes enough difference on centerfire rifle that I could tell a difference (just barely) with my ears, which tells me it likely reduces report by 5-6 decibels. The SDN6, Spcewar, and the Saker all have this feature, so I took their word for it. :lol:

Like this.
Image

Image
I see now! Does it affect accuracy? I'm trying to go for optimal accuracy.

If it doesn't affect accuracy, do you know how to draw it up in Solidworks and know the best method to machine it?
57fairlane wrote:are you planning on welding this together?
I"m on the fence. I'd like to have the ability to take it apart for cleaning.

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Re: 308/7.62 Design review

Post by Dr.K » Wed Apr 16, 2014 4:43 pm

pdx Gun Mechanic wrote:
Dr.K wrote:
pdx Gun Mechanic wrote:Thanks Kyle! As you can probably tell, some of my inspiration came from your posts/build. How did your 308 build turn out? I never could find your post on the end product.

What do you mean by clip?
Little half moon shapes cut out of the entry holes of the baffles. It causes cross jets of gas to push things off center of the bore line, and hold the stuff inside the can just a wee bit longer.

It makes enough difference on centerfire rifle that I could tell a difference (just barely) with my ears, which tells me it likely reduces report by 5-6 decibels. The SDN6, Spcewar, and the Saker all have this feature, so I took their word for it. :lol:

Like this.
Image

Image
I see now! Does it affect accuracy? I'm trying to go for optimal accuracy.

If it doesn't affect accuracy, do you know how to draw it up in Solidworks and know the best method to machine it?
57fairlane wrote:are you planning on welding this together?
I"m on the fence. I'd like to have the ability to take it apart for cleaning.
I was concerned with accuracy issues as well, but alas it is just as accurate as before.

I would also suggest threading the endcaps. Factory cans are welded I suspect mainly for liability issues (I do know the increased strength issue as well), but since your making it yourself, go ahead and go all the way. I've had no issues with threads, I put a drop of red locktite in my threads, and pretend they are welded, but in the event of needing to get in there, a little heat and viola. Not so easy if welded.

Perfect example was when the whiskers popped up, had the can been welded, I'd have had to take an entirely different approach to fix it. Also, I was able to do a comparison of clipped vs. not clipped.

And say sometime down the road one of us comes up with a fantastic new....whatever....lets pretend.....say drill a 3/32 hole halfway up the 3rd baffle for a 50 decibel decrease in report....We would certainly want to get into that silencer to do that! :lol:

I see more advantage to threading the endcaps. If you are taking the thing to war, and need to beat someone to death with it.....well, weld that puppy up tight. :wink:
Kyle O.

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Re: 308/7.62 Design review

Post by calinb » Tue Jul 29, 2014 7:14 pm

Dr.K wrote: Also, I was able to do a comparison of clipped vs. not clipped.
Clipped happened to be better for you but I'm not sure that welding the caps has a downside with respect to the clip or not to clip issue. Technically, if the clipped cones don't work as well as the un-clipped ones, you're still stuck with them with a Form 1. Even if you are able to open-up the can, you won't know what works best until after you clip them and then you're stuck with them.
Last edited by calinb on Fri Aug 01, 2014 2:11 pm, edited 1 time in total.

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Re: 308/7.62 Design review

Post by pdx Gun Mechanic » Thu Jul 31, 2014 5:44 pm

Ok, back to business. Been away but I'm back on track.

Dr. K,

what do you think of the radius I put on the OD of the cone tip? Is this what you are talking about? How does it look to you? If it looks good, I'll work on the clipping next.

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Re: 308/7.62 Design review

Post by Dr.K » Thu Jul 31, 2014 7:08 pm

Almost! Radius goes on the inside of the cone tip!
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Re: 308/7.62 Design review

Post by pdx Gun Mechanic » Thu Jul 31, 2014 7:23 pm

like this?

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