308 design critique

Yes, it can be legal to make a silencer. For everything Form-1, from silencer designs that are easily made, to filing forms with the BATF, to 3D modeling. Remember, you must have an approved BATF Form-1 to make a silencer. All NFA laws apply.

Moderators: mpallett, bakerjw

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

308 design critique

Post by NChobbymachining » Tue Mar 22, 2016 9:19 pm

Hi everyone, I am working on a supressor design primarily for a 24" .308 bolt action. It will also see use on a 10.5" 300blk occasionally. I have been machining for about 6 months now and I use a 7x12 mini lathe and I also have a C2 mini mill. I am confident that I will be able to perform the machining tasks needed to make this suppressor. I have a form 1 that should be approved in the next couple of days if it follows the same trends I have been seeing.

Tube: 7.6" 316 SS DOM 1.5" OD, .065" walls threaded on both ends to 24 TPI
Mount: 303 Stainless threaded to 5/8x24
Endcap: 303 stainless, .7" long, .5" threaded to match tube
Baffles: Stepped 60 degree 303 stainless, 7 .065" thick, blast baffle .08" thick
Spacers: 304 stainless, .030" thick
Bore on everything is .375"

Blast baffle is 2" long, remaining 7 baffles are spread evenly the rest of the way.

End caps and tube come to 8" total. The design should come out around 24oz. If anyone has thoughts on how to get lighter, I would love that.

I would appreciate input on how I could improve this design before I begin making it. There is no rhyme or reason for the number of baffles or their spacing. This is part of the design that I don't understand and would love some input on.

Xray view of internals
Image
Exploded view
Image
Exploded view
Image
Close up of parts
Image

User avatar
fishman
Silent But Deadly
Posts: 1444
Joined: Sun Dec 20, 2015 9:15 pm

Re: 308 design critique

Post by fishman » Tue Mar 22, 2016 9:35 pm

i would either drill holes in the rear cap to lighten it, or hollow it out similarly to the front cap is
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Tue Mar 22, 2016 9:39 pm

fishman wrote:i would either drill holes in the rear cap to lighten it, or hollow it out similarly to the front cap is
Maybe 4 holes at 12,3,6, and 9 oclock? That would lighten it a bit and I could make a wrench to help with dissassembly. Thank you for the tip, I hadn't thought of that.

User avatar
fishman
Silent But Deadly
Posts: 1444
Joined: Sun Dec 20, 2015 9:15 pm

Re: 308 design critique

Post by fishman » Tue Mar 22, 2016 9:46 pm

NChobbymachining wrote:
fishman wrote:i would either drill holes in the rear cap to lighten it, or hollow it out similarly to the front cap is
Maybe 4 holes at 12,3,6, and 9 oclock? That would lighten it a bit and I could make a wrench to help with dissassembly. Thank you for the tip, I hadn't thought of that.
exactly, look at the endcap on the 300 BLK design im working on right now. the 8 holes are for a spanner wrench to aid in disassembly, just like you mentioned. i did 8, 4 would be fine. you could drill the holes from the inside if you dont like the look of them. they would lessen weight but wouldnt help you with disassembly then.

Image
Image
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Tue Mar 22, 2016 9:59 pm

fishman wrote:
exactly, look at the endcap on the 300 BLK design im working on right now. the 8 holes are for a spanner wrench to aid in disassembly, just like you mentioned. i did 8, 4 would be fine. you could drill the holes from the inside if you dont like the look of them. they would lessen weight but wouldnt help you with disassembly then.
I don't have any objection to the way that looks. I will add that in there.

propeine
Silent But Deadly
Posts: 385
Joined: Mon Nov 10, 2014 10:24 am

Re: 308 design critique

Post by propeine » Tue Mar 22, 2016 10:28 pm

.2 is at least twice as thick as it needs to be for your end capt shoulder. .5 in threads is more than necessary on your end cap. Too imo. Since that's all full diameter that should help your weight a bit. Going to ti spacers since ti tubing is cheap would help some but not much. Step cones have more material in them than smooth cones. For that matter switching the shell to TI if you don't already have the material would save a good bit of weight too.

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Tue Mar 22, 2016 10:36 pm

propeine wrote:.2 is at least twice as thick as it needs to be for your end capt shoulder. .5 in threads is more than necessary on your end cap. Too imo. Since that's all full diameter that should help your weight a bit. Going to ti spacers since ti tubing is cheap would help some but not much. Step cones have more material in them than smooth cones. For that matter switching the shell to TI if you don't already have the material would save a good bit of weight too.
I will run the numbers for switching to ti for the spacers. I already have some materials on hand, including the 304 for the spacers but they can be set aside for the future. Ill make the end cap .4" long then with .3" threaded then?

I would go Ti for the tube but I don't think my machine can handle that. I will model up some smooth cones to see what the weight savings would be, but from what I have researched, the stepped baffles will suppress the .308 better.

propeine
Silent But Deadly
Posts: 385
Joined: Mon Nov 10, 2014 10:24 am

Re: 308 design critique

Post by propeine » Wed Mar 23, 2016 12:20 am

NChobbymachining wrote:
propeine wrote:.2 is at least twice as thick as it needs to be for your end capt shoulder. .5 in threads is more than necessary on your end cap. Too imo. Since that's all full diameter that should help your weight a bit. Going to ti spacers since ti tubing is cheap would help some but not much. Step cones have more material in them than smooth cones. For that matter switching the shell to TI if you don't already have the material would save a good bit of weight too.
I will run the numbers for switching to ti for the spacers. I already have some materials on hand, including the 304 for the spacers but they can be set aside for the future. Ill make the end cap .4" long then with .3" threaded then?

I would go Ti for the tube but I don't think my machine can handle that. I will model up some smooth cones to see what the weight savings would be, but from what I have researched, the stepped baffles will suppress the .308 better.
FWIW I have just as easy of a time with Ti as I do stainless. Possibly easier. My machine is a bit larger but I bet you'd be ok.

I think .375 worth of threads and .475-.5625 for total length would be good on your end cap.

I make no claims to sound reduction of smooth vs stepped.

User avatar
fishman
Silent But Deadly
Posts: 1444
Joined: Sun Dec 20, 2015 9:15 pm

Re: 308 design critique

Post by fishman » Wed Mar 23, 2016 10:03 am

NChobbymachining wrote:
propeine wrote:.2 is at least twice as thick as it needs to be for your end capt shoulder. .5 in threads is more than necessary on your end cap. Too imo. Since that's all full diameter that should help your weight a bit. Going to ti spacers since ti tubing is cheap would help some but not much. Step cones have more material in them than smooth cones. For that matter switching the shell to TI if you don't already have the material would save a good bit of weight too.
I will run the numbers for switching to ti for the spacers. I already have some materials on hand, including the 304 for the spacers but they can be set aside for the future. Ill make the end cap .4" long then with .3" threaded then?

I would go Ti for the tube but I don't think my machine can handle that. I will model up some smooth cones to see what the weight savings would be, but from what I have researched, the stepped baffles will suppress the .308 better.
Even sherline lathes can handle titanium, yours should do it, you just need to take light cuts with fast feed.
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Wed Mar 23, 2016 3:09 pm

After lightening up the end cap and mount, and switching the baffles from stepped to cones, the estimated weight is 17.25 oz.

Switching the tube and spacers from SS to Ti brings the weight down to 12.5 oz. The new tube would cost $29.25 vs the $17.23 using 316 Stainless. Those prices are for Grade 9 Ti. The extra $12 would certainly make sense if Grade 9 would be strong enough.

propeine
Silent But Deadly
Posts: 385
Joined: Mon Nov 10, 2014 10:24 am

Re: 308 design critique

Post by propeine » Wed Mar 23, 2016 3:31 pm

NChobbymachining wrote:After lightening up the end cap and mount, and switching the baffles from stepped to cones, the estimated weight is 17.25 oz.

Switching the tube and spacers from SS to Ti brings the weight down to 12.5 oz. The new tube would cost $29.25 vs the $17.23 using 316 Stainless. Those prices are for Grade 9 Ti. The extra $12 would certainly make sense if Grade 9 would be strong enough.
Grade 9 is fine and likely all you're going to find. Gr5 is barstock, Gr9 is tube stock. Just make sure its not CP2

User avatar
T-Rex
Silent But Deadly
Posts: 1849
Joined: Wed Oct 29, 2014 4:38 pm
Location: CT - The AntiConstitution State

Re: 308 design critique

Post by T-Rex » Wed Mar 23, 2016 3:38 pm

The Ti will be stronger (yield strength), initially.
However, the SS will hold its strength through a greater heat range.
If you don't plan on getting the can insanely hot, for extended periods, the Ti will pay off.

If you want the best of both worlds, go with 17-4.
More work to turn from bar stock, but the results are worth it.

My $.02
Completed Builds www.silencertalk.com/forum/viewtopic.php?t=79895
Burst Calculator www.engineersedge.com/calculators/pipe_bust_calc.htm
Silencer Porn www.instagram.com/explore/tags/silencerporn/

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Wed Mar 23, 2016 4:05 pm

propeine wrote:
NChobbymachining wrote:After lightening up the end cap and mount, and switching the baffles from stepped to cones, the estimated weight is 17.25 oz.

Switching the tube and spacers from SS to Ti brings the weight down to 12.5 oz. The new tube would cost $29.25 vs the $17.23 using 316 Stainless. Those prices are for Grade 9 Ti. The extra $12 would certainly make sense if Grade 9 would be strong enough.
Grade 9 is fine and likely all you're going to find. Gr5 is barstock, Gr9 is tube stock. Just make sure its not CP2
I was looking at Grade 9 from titanium joe. For me, using the Grade 5 would be cost prohibitive.

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Wed Mar 23, 2016 4:10 pm

T-Rex wrote:The Ti will be stronger (yield strength), initially.
However, the SS will hold its strength through a greater heat range.
If you don't plan on getting the can insanely hot, for extended periods, the Ti will pay off.

If you want the best of both worlds, go with 17-4.
More work to turn from bar stock, but the results are worth it.

My $.02
It will be used mostly slow fire on the .308 shooting maybe 50 rounds/hr, very rarely do I shoot multiple shots in rapid succession with that one.

On the 300 blk, it might see heavier use. It would need to be able to handle 20-30 rounds of supersonic in rapid succession. (Under 10 seconds) The 300 blk is mostly used for competition and practice. I usually set up a 5-10 target course of fire and roll through it as quickly as I can.

The can will also be mounted on .223s occasionally. One is a 20" SPR type rifle and the other is a 16" competition rifle.

Will the Ti be able to take that abuse? For me, a typical range day includes about 50 rounds of the .308 and 200 rounds of 300 blk. I would like all of them to be suppressed.

In regards to the 17-4, it weighs about the same as 316 (.280 lbs/in3 vs .289 lbs/in3). How would it be the best of both worlds?

User avatar
fishman
Silent But Deadly
Posts: 1444
Joined: Sun Dec 20, 2015 9:15 pm

Re: 308 design critique

Post by fishman » Wed Mar 23, 2016 4:18 pm

NChobbymachining wrote:
In regards to the 17-4, it weighs about the same as 316 (.280 lbs/in3 vs .289 lbs/in3). How would it be the best of both worlds?
17-4 is stronger than other stainless so you could make it thinner, therefore lighter. it would also take heat cycles better than the titanium
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Wed Mar 23, 2016 4:20 pm

fishman wrote:
NChobbymachining wrote:
In regards to the 17-4, it weighs about the same as 316 (.280 lbs/in3 vs .289 lbs/in3). How would it be the best of both worlds?
17-4 is stronger than other stainless so you could make it thinner, therefore lighter. it would also take heat cycles better than the titanium
Oh I see. I hadn't considered it could be thinned out. Would the titanium hold up to the use I would like it to?

User avatar
fishman
Silent But Deadly
Posts: 1444
Joined: Sun Dec 20, 2015 9:15 pm

Re: 308 design critique

Post by fishman » Wed Mar 23, 2016 4:24 pm

NChobbymachining wrote:
fishman wrote:
NChobbymachining wrote:
In regards to the 17-4, it weighs about the same as 316 (.280 lbs/in3 vs .289 lbs/in3). How would it be the best of both worlds?
17-4 is stronger than other stainless so you could make it thinner, therefore lighter. it would also take heat cycles better than the titanium
Oh I see. I hadn't considered it could be thinned out. Would the titanium hold up to the use I would like it to?
i dont have the experience necessary to answer that.

if i had to guess, 308 slow fire would be fine. and 300 blackout subsonic rapid fire should be alright, but idk if i would rapid fire supersonic rounds.

you should make the blast baffle out of 17-4. period. no reason not to.
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647

User avatar
CMV
Silent But Deadly
Posts: 750
Joined: Thu Feb 09, 2012 6:31 pm
Location: NC

Re: 308 design critique

Post by CMV » Wed Mar 23, 2016 6:53 pm

What part of NC?

Is your tube already threaded? Might not be able to do that on a 7x12 - they run out of real estate pretty quick :)

Keep in mind 303 isn't as 'stainless' as one would expect - it will require regular maintenance. Machines nice though.
--------------------------------------

"Sorry but you cannot use search at this time. Please try again in a few minutes"
"This board is currently disabled"
These things make me :(

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Wed Mar 23, 2016 8:12 pm

CMV wrote:What part of NC?

Is your tube already threaded? Might not be able to do that on a 7x12 - they run out of real estate pretty quick :)

Keep in mind 303 isn't as 'stainless' as one would expect - it will require regular maintenance. Machines nice though.
I am in Raleigh. I have measured and I can just squeeze in a 10" tube for threading.

I have done some work with 303 and it is only kinda stainless.

User avatar
silencer_kid
Silent But Deadly
Posts: 315
Joined: Wed Jan 15, 2014 10:58 pm

Re: 308 design critique

Post by silencer_kid » Wed Mar 23, 2016 11:58 pm

CMV wrote:What part of NC?

Is your tube already threaded? Might not be able to do that on a 7x12 - they run out of real estate pretty quick :)

Keep in mind 303 isn't as 'stainless' as one would expect - it will require regular maintenance. Machines nice though.
he could still us the 303ss for the build, but i would perhaps add a coating
http://www.cerakotehightemp.com/

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Thu Mar 24, 2016 12:28 am

silencer_kid wrote:
CMV wrote:What part of NC?

Is your tube already threaded? Might not be able to do that on a 7x12 - they run out of real estate pretty quick :)

Keep in mind 303 isn't as 'stainless' as one would expect - it will require regular maintenance. Machines nice though.
he could still us the 303ss for the build, but i would perhaps add a coating
http://www.cerakotehightemp.com/
I am set up to do cerakote but I don't think it would last very long inside the can.

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Thu Mar 24, 2016 12:31 am

fishman wrote:i dont have the experience necessary to answer that.

if i had to guess, 308 slow fire would be fine. and 300 blackout subsonic rapid fire should be alright, but idk if i would rapid fire supersonic rounds.

you should make the blast baffle out of 17-4. period. no reason not to.
I don't want to have to worry, and I am not sure if I will make another after the new rules go into effect so I will stick with the stainless for the tube.

User avatar
silencer_kid
Silent But Deadly
Posts: 315
Joined: Wed Jan 15, 2014 10:58 pm

Re: 308 design critique

Post by silencer_kid » Thu Mar 24, 2016 8:31 am

NChobbymachining wrote:
silencer_kid wrote:
he could still us the 303ss for the build, but i would perhaps add a coating
http://www.cerakotehightemp.com/
I am set up to do cerakote but I don't think it would last very long inside the can.
add a thin blast chamber spacer, and 1st baffle out of a better material, then coat the rest. should survive a lifetime of use.
or what about hard chrome just the 1st baffle and tube blast chamber section (dip to plate). it has a service temp to ~1150F.

NChobbymachining
Member
Posts: 42
Joined: Tue Mar 22, 2016 8:23 pm

Re: 308 design critique

Post by NChobbymachining » Thu Mar 24, 2016 2:23 pm

silencer_kid wrote:
NChobbymachining wrote:
silencer_kid wrote:
he could still us the 303ss for the build, but i would perhaps add a coating
http://www.cerakotehightemp.com/
I am set up to do cerakote but I don't think it would last very long inside the can.
add a thin blast chamber spacer, and 1st baffle out of a better material, then coat the rest. should survive a lifetime of use.
or what about hard chrome just the 1st baffle and tube blast chamber section (dip to plate). it has a service temp to ~1150F.
Its worth a shot. Ill coat the 7 baffles after the blast baffle and see how it holds up. Ill order some 17-4 and use that for the blast baffle.

User avatar
fishman
Silent But Deadly
Posts: 1444
Joined: Sun Dec 20, 2015 9:15 pm

Re: 308 design critique

Post by fishman » Thu Mar 24, 2016 2:28 pm

why didnt you thread the rear cap all the way through with the threads that attach to the barrel? doing so would cut some weight.
300 blackout form 1: http://www.silencertalk.com/forum/viewtopic.php?f=10&t=137293

5.56 form 1:
http://www.silencertalk.com/forum/viewtopic.php?f=10&t=141800&p=955647#p955647

Post Reply