Form 1 5.56 can--first stages of design questions

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.

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noscoe30
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Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

Hello,

I e-filed my form 1('s) and am starting work on my 5.56 can. I have selected 6" as my overall length.

I was going to use a silencerco saker maad 51 tooth mount for my muzzle end. I think its threaded 36tpi, does anybody know for sure?

For material I am planning to use a chunk of 17-4 H900 2"od bar stock for my tube. Finished OD will probably match the saker mount, 1.5". Not sure on wall thickness. It would be made so the saker mount fits the muzzle end, and the blast chamber/outer tube would be one solid piece. Baffles inserted from the front (resting against a stop inside the tube), and either a welded or threaded cap.

I have a friend that is certified in 17-4 welding but doesn't know the effects of welding the h900 state if it is not heat treated after. I wasnt planning on heat treat after welding, so I am leaning towards a threaded end cap. The saker has a threaded mount, so is a threaded end cap such a bad thing?

Will 17-4 h900 hold up as a blast baffle? I was going to be using the aac brake-out mounts for their built in sacrificial properties. I know those are 17-4 but not sure of heat treat.

I was also looking into using stellite for hardfacing the baffles. Does silencerco cast their baffles? What stellite alloy would be the best? I was thinking 1 or 6. Has any form 1'r hardfaced their baffles?

As for use and application, it will be on short barrels with moderate rates of fire.


Thanks for the wonderful environment. I will be posting lots of pictures on the way.

Mitch
noscoe30
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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

I forgot to mention that my form 1 came back approved.

Any ideas of the durability of a full 17-4 h900 build?
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Re: Form 1 5.56 can--first stages of design questions

Post by RPM509 »

I can't answer your questions, but am interested in following along with your build.
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Re: Form 1 5.56 can--first stages of design questions

Post by Bendersquint »

noscoe30 wrote:I forgot to mention that my form 1 came back approved.

Any ideas of the durability of a full 17-4 h900 build?
17-4 will be plenty strong, its what alot of the industry used before Inconel became the standard.

I would definitely do some post treatments to it though so its strong for a lifetime of use.
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Re: Form 1 5.56 can--first stages of design questions

Post by Samson104 »

I did a full 17-4 build and it has held up perfect to ALOT of abuse.
I only bothered treating the break/mount.
I've done back to back 90 round mag dumps with it on a full auto 12.5" M4 several different times , the brake has some wear the brake but maybe 5%.
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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

Thanks for the replies!

The material I have is already in the h900 condition. Do you think h1150 would be better? I think it ends up softer but has better temprature capability. I am thinking a threaded "take apart" Would be best so I don't need to worry about welding
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Re: Form 1 5.56 can--first stages of design questions

Post by Capt. Link. »

Read up on 17-4-Ph-900 Mr.B was giving you a hint for durability and long life.
The only reason after 243 years the government now wants to disarm you is they intend to do something you would shoot them for!
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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

"post treatments"

Not sure what that meant. H900 would be considered a post treatment. My material is already in the h900 state. Are there other treatments that would be more suitable for a 556?
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Re: Form 1 5.56 can--first stages of design questions

Post by delta9mda »

Samson104 wrote:I did a full 17-4 build and it has held up perfect to ALOT of abuse.
I only bothered treating the break/mount.
I've done back to back 90 round mag dumps with it on a full auto 12.5" M4 several different times , the brake has some wear the brake but maybe 5%.
samson knows a thing or two here.
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Re: Form 1 5.56 can--first stages of design questions

Post by Rich V »

noscoe30 wrote:Thanks for the replies!

The material I have is already in the h900 condition. Do you think h1150 would be better? I think it ends up softer but has better temprature capability. I am thinking a threaded "take apart" Would be best so I don't need to worry about welding
Mitch
With 17-4 SS the H900 temper is going to be the strongest (yield strength) and hardest version. As you go to higher heat treats you lose yield strength and hardness and gain toughness (Charpy V-notch).

17-4 has 2-3x the strength of 300 series SS even in the annealed state so from a strength perspective any temper of 17-4 will work well in a suppressor. What the H900 version gets you is a much harder alloy. H900 is ~ 44 Rc, if you go to H1150 it drops to ~ 33 Rc. That is a significant drop and one that will ultimately show up in significantly more baffle erosion over time.
As for gaining toughness the H900 appears to be plenty tough for suppressor use.

Stay with the H900 you have in hand no need to change to a different temper.

Read these for some background in 17-4 properties.
http://www.azom.com/article.aspx?ArticleID=4220
viewtopic.php?f=10&t=130987&sid=19ab654 ... fdc816a794
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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

I just did a hardness check on my material. I had a suspicion that it wasnt actually h900. I had to turn the OD from 2.25 to 1.625 so I can run it in my 16c collet chuck. I was expecting to wear out an insert (I was running the manual lathe) but it ran fine.

It seems to be coming in at 33-34rc so I think it was actually h1100 or h1150.

I imagine this will be fine for the tube and end cap. Should I select a different material for the baffles?

Also, for wall thickness I was going to go with .080 for the blast chamber and .040 for the tubing around the baffles. The baffles were going to be simple cones with spacers built in. maybe .040 wall on the spacers so it would be .080 throughout. What are your thoughts? I was planning on having the step internally and that would hold the baffles from sliding towards the rear.
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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

ALSO!

I was thinking of hardfacing the baffle wear areas. Has anybody tried that with stellite 6?
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Re: Form 1 5.56 can--first stages of design questions

Post by curtistactical »

I just do it on my blast baffle but in a different way. The outer body of my blast baffles are 17-4, I cut a c'bore in the back face and tig weld a complete Inconel face into it that is .06 thick at the bore. The Inconel takes all the abuse and it cuts down on cost using 17-4 as the body material.
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Re: Form 1 5.56 can--first stages of design questions

Post by Samson104 »

You are trying to make it way way to complicated , if you are worried about the can not lasting don't.
Make your blast chamber and end cap all once piece with .050" walls , weld your blast baffle to the blast chamber. Make your out tube .050" , press fit the blast chamber into the tube and fully weld it together.
Every .625" ahead of the blast baffle drill 4 , 3/16" holes 90 deg appart.
make your cones with a 1/4" wide skirt. Your baffels should be .002" wider the the ID of the tube so it is a press fit. Press the cones into the tube so that you can plug weld the baffels inside the tube.

If you want the reduce the wear on your blast cone then make a internal brake attachment that will take the brunt.

Give me a few and ill dig up some pics.
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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

Here is what I have for the outer tube so far.

Currently it is a 1.625 OD tube with a 1" ID. This is so I can fit it in my lathe collet. The last operation will be turning the OD to size.

I have .065 for blast chamber thickness, and .050 for baffle area thickness. The baffles will be 60 degree cones, with spacers built in. Looks like Ill have 3 or 4. Can overall length is 6" (not including the non controlled saker 51 tooth mount)

The end cap will probably be threaded on. That way when my annealed 17-4 blast baffle starts opening up I can weld it back up with some hardfacing rod. I am thinking external threads on the tube with an internal threaded cap. Maybe make it compatible with the saker end cap (the replaceable one)


Also the saker mounts have a 10 degree taper, and 32TPI with a major diameter of 1.373. It was done with a full profile insert. I imagine they call it a 1.375-32tpi.


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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

What does everybody think of using carpenter custom 465 for the baffles? In the annealed condition.
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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

Im now at the step where I need to figure out how to hold the guts in. I really want to make a take-apart can so I can experiment with tig hardfacing if I have a lot of wear.

Right now the wall thickness in the baffle area is .050 tube OD 1.5"

What type of end cap would you make? Internal threaded? It looks like a 1.43-36 3B 1.4387/1.4300 major would give good meat around the tube at .031 wall or maybe a 1.435-32 3B 1.4444/1.4350 major at .027 wall. Those would both minor at 1.400", the tube ID.


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Re: Form 1 5.56 can--first stages of design questions

Post by Wicked »

noscoe30 wrote:ALSO!

I was thinking of hardfacing the baffle wear areas. Has anybody tried that with stellite 6?
Yes. Laser cladded +.010" thick Stellite 6 face to the blast baffle of 17-4ph H900. No idea how well it works, as the can is fully welded. It made me feel better about doing it though.

Not a baffle, but will give you an idea of the welded surface. Diameter is .50" for reference.

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Re: Form 1 5.56 can--first stages of design questions

Post by curtistactical »

Wicked wrote:
noscoe30 wrote:ALSO!

I was thinking of hardfacing the baffle wear areas. Has anybody tried that with stellite 6?
Yes. Laser cladded +.010" thick Stellite 6 face to the blast baffle of 17-4ph H900. No idea how well it works, as the can is fully welded. It made me feel better about doing it though.

Not a baffle, but will give you an idea of the welded surface. Diameter is .50" for reference.

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Re: Form 1 5.56 can--first stages of design questions

Post by Rich V »

I have used T-15 high speed steel inserts for an integral muzzle brake & the blast baffle. I contacted Arthur Warner http://www.arwarnerco.com/ and had them cut several "washers" from 1/8 inch T-15 plate. These were then trued on my lathe with a grinder and high temp silver soldered into pockets cut in 17-4 SS. These show absolutely no wear after many rounds of 223. No surprise since T-15 has a Rc of ~65 and has excellent hot hardness.
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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

Looks like I am getting close.

Outlet of the silencer will be threaded the same as the inlet, 1.375-32. I chose this because the saker uses that to hold itself to the mount, which is high pressure. Construction will be 100% 17-4 condition A. If I can find a local heat treater with an FFL I will bring it to H900. I understand I need to be aware of stress corrosion cracking if I leave it in condition A.

Total of 6, 60 degree cones. No plans for clipping as of right now, but I should be able to add them later. Maybe leave the blast baffle symmetrical, then clip the rest?

Wall thickness in blast chamber area is .110". Wall thickness around baffles is .080" and integrated baffle-cone-spacers is .040 wall thickness. Blast baffle thickness is .060", the 4 baffles between first and last are .040" and the last baffle is .035" End cap thickness is .100", this is probably a little thick. Maybe face groove the inside to relive it to .050 thick. Maybe integrate a cone into the end cap?

Bore size is .260" thru. Should I open up the last few baffles more than the first?

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Re: Form 1 5.56 can--first stages of design questions

Post by noscoe30 »

I am almost done. Tune is made out of solid and is currently .110 wall at the blast chamber and .080 wall around baffles. I am currently at 22 ounces with saker trifecta mount. I need to lose 3-4 oz. should I reduce the wall thickness?

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Re: Form 1 5.56 can--first stages of design questions

Post by T-Rex »

you should have no problem decreasing the wall by half, all around.
You could keep the blast wall a hair thicker (.065")
But the baffle walls are also supported by the cone's skirt so don't worry about shaving some extra off.

Machining looks great.
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Re: Form 1 5.56 can--first stages of design questions

Post by esh21167 »

Nice! Very similar to my plan.
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Re: Form 1 5.56 can--first stages of design questions

Post by esh21167 »

Editing my question. Are the holes in the endcap deliberately connected into the last chamber? That does not appear to be the case in the model. Are they for assembly/disassembly? Would there be any benefit to having holes on the end cap that do intersect with the last chamber?
Last edited by esh21167 on Wed Sep 09, 2015 7:12 pm, edited 4 times in total.
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