Integral Suppressed Sten Form 1 Idea

[Kujo]

I am brand new to the forum, and Form 1 suppressors, but I am currently building a Sten MK2 from a parts kit, and Indianapolis Ordnance’s semi auto receiver and bolt kit, and am fooling around with the idea of integrally suppressing it. I do not want to thread the 16 inch barrel because it would be obnoxiously long with a can, and I do not want to do an 8 inch threaded barrel because then I would need to Form 1 it twice, so the plan would be to permanently fix a 16 inch tube around an 8 inch barrel and turning that into the suppressor. Will this idea be approved as a form 1?
This is a simple drawing I did to illustrate the idea. If you are familiar with the Sten then you know it uses an incredibly simple barrel nut system to attach the barrel, and I think this would make a good host for an integral suppressor. I could use an existing barrel nut/handgaurd, which happens to be nearly identical in size to a D Cell tube, cut the handgaurd back to the end of the threads of the nut, weld in the suppressor tube, then weld this whole assembly to the 8 inch barrel so it would be permanently 16 inches overall. So far I am planning on using freeze plugs as baffles, unless you guys have a better suggestion. I do also realize my barrel porting location is terrible and do not know why I drew them there, but you get the idea.

Any help and feedback would be appreciated! I know this sketch is rough, but this is my first experience with form 1 suppressors and I just want to learn about it and know if this is a feasible idea. Thanks!

[T-Rex]

No reason your ideas shouldn't work.
Just make sure the measurement from a closed bolt face to the suppressor exit is >15.99999in.
You can simply pin/weld the barrel nut to the barrel and the tube to the barrel nut. No circumferential welds are necessary, unless you want them.
With the availability of great parts, I'd shy away from freeze plugs.
I know they can get pricey, but do 2 Ti cups, followed by all Al.
Cones or Radials. They both work great for 9mm.
You don't need crazy volume (OD) as you have plenty of length. 1.375 would work fine.
Unless you intend to reduce bullet velocity, the porting is exactly where it needs to be.

[Kujo]

Wow thanks for the reply! That does answer some question for me, because I was even away that proper comes or baffles were available. Do you use the two ti cups first to take the brunt of the muzzle blast, and then aluminum cups work fine after that?

[Kujo]

Also, to make this possible I’d have to locate a 14.5 inch tube, but the longest I can find available so for is 11.6 inches. Does anybody know where I could get one long enough for my project, or is there another option I should be looking towards? For my purposes I’d like D Cell size, simply because it will match the OD of the Stens receiver and look nicer.

[Capt. Link.]

I've had the pleasure of working on several originals and clones of the Sten over the years.If I were to build a semi-auto version the barrel would get ported for velocity control.Suppressor tubes can be made from D.O.M. tubing.K baffles or ported cones should provide plenty of suppression set up as described.

A very worthy project keep the group in the loop.

[T-Rex]

Also, to make this possible I’d have to locate a 14.5 inch tube, but the longest I can find available so for is 11.6 inches. Does anybody know where I could get one long enough for my project, or is there another option I should be looking towards?

You can contract a local machine shop to do the work or make the parts. The only caveat is that you must be present when work is performed and take all parts with you and keep them under your supervision. This is specifically in mention to silencer parts. You can have them make you a 14.5in tube, w/ appropriate threads, for use as a Solvent Trap , w/o issue.

For my purposes I’d like D Cell size, simply because it will match the OD of the Stens receiver and look nicer.

You have the option of matching the receiver 38mm[1.49] or the barrel bushing 35mm[1.377]
If you match the barrel bushing, you won't lose the factory front sight, correct?

[Kujo]

I've had the pleasure of working on several originals and clones of the Sten over the years.If I were to build a semi-auto version the barrel would get ported for velocity control.Suppressor tubes can be made from D.O.M. tubing.K baffles or ported cones should provide plenty of suppression set up as described.

A very worthy project keep the group in the loop.

Thanks man I definitely will!

[Kujo]

Thanks T-Rex! I was curious how having someone else do the work would work out. also, the front sight and barrel bushing shouldn’t be harmed regardless I believe

[Kujo]

So I have a couple more questions. First off, what would be the best way to provide a base for my first baffle? It would just an unthreaded barrel inside of a d Cell tube, and all I can think to do is place a unformed freeze plug with a hole larger than the bore, but smaller than the barrel O.D., then build off of that.
Secondly, I plan on a potted barrel so there is volume around the barrel, and approximately 8 inches of space for baffles in front of the barrel. How many baffles, and what spacing between the baffles, would be appropriate?

[Kujo]

I decided to CAD my suppressor design using OnShape. Everything but the baffles and spacing are to scale and properly sized, but because I do not know the actual dimensions of the baffles i plan on using I just winged it. Anyways, here they are for anyone interested. This is the barrel, the silence tube, and then the assembly both solid and transparent.

[#40Fan]

Who's cones and what size do you plan on using? I might have the dimensions for them.

[fishman]

Looks good. Those barrel ports are a little close to the chamber unless you want to try to keep 124 grain ammo subsonic

[T-Rex]

You should be able to keep your muzzle to first cone distance pretty small. You're dealing with low pressure gases, which you've already reduced with the porting. You can tighten-up the baffle spacing for 9mm. Not sure what you've allotted, but it looks larger than necessary. Shoot for around 1/2". You could start larger and reduce along the way or go one consistent size.

[Kujo]

Who's cones and what size do you plan on using? I might have the dimensions for them.

I haven’t really settled on any yet, but I modeled these more or less after the 1.347” cones from totality industries, but I’d love to know whatever dimensions you can get me!

Looks good. Those barrel ports are a little close to the chamber unless you want to try to keep 124 grain <a class="vglnk" target="_blank" href="http://i.viglink.com/?key=00da2735c1c2f ... %2Fspan%3E" rel="nofollow"><span>ammo</span></a> subsonic

That was a feature subject to change, but I think I’m leaning towards the idea of being able to shoot any weight very quietly out of this barrel. In case I do change it, where would you recommend I place them to maintain supersonic speeds with 124gr rounds? Maybe halfway, or near the muzzle? I’d imagine there would be some suppression benefits to keep them as far back as possible.

You should be able to keep your muzzle to first cone distance pretty small. You're dealing with low pressure gases, which you've already reduced with the porting. You can tighten-up the baffle spacing for 9mm. Not sure what you've allotted, but it looks larger than necessary. Shoot for around 1/2". You could start larger and reduce along the way or go one consistent size.

Thanks! I wasn’t quite sure what spacing to use, but that does clear things up. I’m this particular design they are so far apart because I couldn’t figure out how to put them closer together in the program, but I still would have guessed larger than 1/2”.

[T-Rex]

That was a feature subject to change, but I think I’m leaning towards the idea of being able to shoot any weight very quietly out of this barrel.

If you port near the chamber, it will reduce projectile velocity.
Here's the rub.
Bullets that are usually above the speed of sound will be reduced to (based on size and Qty of ports) around or under 1050fps.
Bullets that are normally subsonic, ie: 147 & 158grn, could be too slow to reliably shoot. You may end up w/ squib rounds (stuck in barrel)
For reference, you do not shoot these weight bullets from an MP5SD.

If you port near the muzzle, the initial gas volume entering the forward suppressor portion (baffled section) will be greatly reduced.
This "lightens the load" on the baffles and can help performance, greatly.
Conversely, it won't do anything for bullet velocity and the lower weight, faster projectiles, will still go supersonic and create a downrange crack.

There are machinable options to create adjustable style gas bleeds, but for the Form 1 guy buying "off the shelf" parts, you can be limited.
John A has done it with screws, to allow the shooting of various weight projectiles, while mainlining a specific function.

[Kujo]

I’m very glad you said that because I could have made a mistake, I never thought about the posibility of a squib with the heavy bullets, so I will probably port much closer to the muzzle. If the rounds are going to be subsonic, I might as well be able to throw the heaviest bullet possible.

[T-Rex]

Yeah, it's a trade-off.
The lower weight stuff is almost always cheaper, but porting closer to the chamber leaves the coaxial volume dirtier.

[Kujo]

That’s a very good point, but I definitely think I’d prefer the option to run any weight bullet, even if the 124s stay supersonic. This is my first suppressor, so it will still be an improvement over what I’m used to, and if I want super quiet I’ll run 147s. I’m glad that came up before I put holes in a barrel.

[#40Fan]

1.347" Totality 60° specs

1.347" Diameter at base
.110" Skirt height
1.221" Diameter at cone base
.500" Diameter at cone tip
.740" Cone height

[alordnapa]

Are you concerned that so may ports, so closely spaced and in a linear fashion, might create potential mechanical failure points? Ports get hot!

[Kujo]

1.347" Totality 60° specs

1.347" Diameter at base
.110" Skirt height
1.221" Diameter at cone base
.500" Diameter at cone tip
.740" Cone height

Wow thanks! I will be updating my CAD drawing with all those for sure.

Are you concerned that so may ports, so closely spaced and in a linear fashion, might create potential mechanical failure points? Ports get hot!

Honestly, never even crossed my mind because I’ve seen it done on designs like the MP5SD, with possibly even more ports. Given that I have now decided to move them closer to the muzzle, and because the barrel is only 7.8” and well supported at both ends with decent wall thickness, I can’t imagine it being a problem.

[Kujo]

Here is a new, updated, CAD design after some very helpful input from you guys. Ports were moved forward to allow the use of all bullet weights, but 124s will still stay supersonic I’d imagine. Also, the baffles and spacers are all to scale. The first baffle is placed with its nose .5 inches away from the muzzle, the next five baffles are spaced .625 inches apart, and the last 4 baffles are spaced .5 inches apart. This makes 10 baffles in about 7.5 inches. It also has an expansion chamber of 6 inches before the baffles.
I have never made a suppressor before, but i feel like this has the potential of being a very quiet design.

[T-Rex]

The barrel ports are acting as a pseudo muzzle brake, spilling the inital release into the OB reflex volume. You should be able to pull your blast baffle closer to the crown. Also, unless you plan for FA use, a 5/8" spacing seems a bit on the larger side for 9mm. I'd stick to 9/16" and under.

Next, you'll need to decide on a baffle clipping scheme.

[Kujo]

The barrel ports are acting as a pseudo muzzle brake, spilling the inital release into the OB reflex volume. You should be able to pull your blast baffle closer to the crown. Also, unless you plan for FA use, a 5/8" spacing seems a bit on the larger side for 9mm. I'd stick to 9/16" and under.

Next, you'll need to decide on a baffle clipping scheme.

I went with the spacing I did simply because it made the 10 baffles a perfect fit in the length of tube I’m working with, how beneficial would it be for suppression to tighten everything up and add a couple more baffles you think? I’m not sure how many a typical 8 inch 9mm suppressor uses.
And I’ve started researching baffle clipping design a little bit, but I do need to research a bit more before I make a decision. However, the general consensus I see tends to be that the design is really not all that important as long as you make something to disrupt the flow.

[T-Rex]

You wouldn't need to add any baffles.
You could:
Make them all 9/16
Move the BB 1/4" closer to the muzzle
Leave the last baffle to end cap distance +1/4"

Either way, I think you'll have a winner.

Clipping can often impact bullet stability. Thought should be put into it.