Integral Suppressed Sten Form 1 Idea

[Kujo]

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.

That’s a good point. For some reason In my mind I wanted the last baffle to mate up to the end cap, but really there is no sense in that, the end cap would act as a psuedo baffle anyways. I will CAD it up that way and see what I think.
As far as bullet stability and clipping goes then, would recommend a symmetrical clipping on both sides of the cone, to hopefully even out any negative impact it may have on the bullet?

[Kujo]

Well, version 3 of the suppressor. I really appreciate the feedback, when I’m actually ready to start throwing this thing together it should be completely figured out.

[T-Rex]

Asymmetrical should work great.
I use a cutter equal to half the bore diameter and cut 100%, if not more, of the cutter diameter.
Symmetrically clip the blast baffle or don't clip at all.

So, what are you going to do about parts?
I think I read that SDTA will cut you a tube at any length you want.
Who's cones, skirts, and caps?

Remember, you can use 2 smaller skirts to equal your spacing (ie: 1/4 & 5/16 = 9/16) and move them around, inside the can, to try different configurariotns. So long as you're using all the pieces and not making new or having leftovers, you're legal.

[Kujo]

Am I correct in thinking you don’t typically cut the first and last baffle?
I will have to look into SDTA some more, because the biggest issue I was having was locating a tube given that I need one to be 14.5 inches. As for cones and skirts go, I based my CAD drawings off of Totalities products, but I’d be open to suggestions still given that using totalities products the internals of this can alone are upwards of $200. I have not thought about caps because I hadn’t sourced a tube yet. I will definitely take your suggestion to use smaller spacers to add up to what I need, it seems like the best option.

[T-Rex]

I don't always clip the first (centerfire rifle), but I always do the last.

Seriously consider Aluminum parts (SS or Ti for blast or first 2)
It will drop both your weight and final cost.
Aluminum is absolutely strong enough for 9mm.

I have no experience with any of the solvent trap retailers as I make my own parts. I'm sure there's plenty of reviews for your intended seller(s).

[Kujo]

What I priced was for two ti baffles and 8 aluminum, per your earlier recommendation actually, and all the required spacers. All I should have to have machined is what I would describe as a muzzle adapter, and have the end of the muzzle turned down slightly for it.

[#40Fan]

Catch one of TI's sales to help save a few bucks.

[Kujo]

I wanted to share something I found interesting, but clearly everyone is entitled to their own opinion. I joined a Form 1 builders group on Facebook, and my design was met with a lot of criticism, and entirely opposite input form what I have been given here. Frankly, I trust the minds of everyone on this forum more than a Facebook group, but here are some of the views they shared with me there.

1. They would NEVER use aluminum in a 9mm can. It is inferior, and will erode prematurely.
2. My spacing is too tight, especially the distance from muzzle to first baffle. I still need a larger blast chamber, even with my porting and it being a 9mm.
3. 10 baffles is an obnoxious amount for a can this size, Low pressure cartridges do not need more baffles as long as your baffle design is on point, and by using so many baffles it implies my baffles are sub par, but they are your standard 60 degree cone which are pretty well proven in my mind.
4. My porting near the muzzle is apparently insulting to them, their ancestors, and their god.
5. Porting near the muzzle will not utilize any of the expansion chamber before my baffles, and will not be advantageous for suppression.
6. I could still use 147gr projectiles even with the porting just in front of the chamber, because my design has more back pressure than something like an MP5SD. (I did not understand this statement to be honest, but maybe I just dont understand the design well enough)

So, do you guys think any of these statements hold any water? The only one I see at all would be that the porting near the muzzle is not going to take advantage of the expansion chamber around the barrel, but even then it will be easier for the gasses to fill the empty chamber than it will be to go through the muzzle adapter which will have 8 to 12 holes drilled in it to allow the gasses through. Would it make sense to put the ports closer to halfway down the barrel, or maybe much fewer ports along the entire length of the barrel? I know we have already discussed these ports extensively, but it has me thinking again.

[T-Rex]

I just gave you a long reply and the forum ate it. Here's a brief review:

1. Full Auto silencers have been made from 100% Aluminum for over 50 years.
2. Porting negates the need for a blast baffle.
3. Almost all, full size, 9mm silencers, made form a large Mfr, are going to have 8-12 baffles. Why? Because that's what's needed. They could charge the same price, put fewer baffles, decrease their Mfr'g costs, and increase profit, but they'd have a poorly performing design. Baffles are where the money's made
4. They don't understand silencer science
5. The porting would act as a pseudo brake, as stated earlier. A blast spacing isn't needed. However, further gas disruption is always a plus. You need to weigh the length vs reward scenario.
6. Ridiculous claim. Back pressure is irrelevant until the bullet has left the muzzle. The chamber porting decreases the powder's ability to impart pressure on the projectile, reducing it's rate of travel. The bullet to bore friction is a constant and, w/o the needed pressure, further reduces the bullets rate of travel. This gets you close to a squib round. Very dangerous when you're not accounting for every round sent downrange.

The most effective place to port is immediately after the powder has reached 100% burn. Very difficult to do with varying weights and Mfr's of ammo. If you're reloading, you can easily find the longest length needed and port there.


ETA: I noticed the percentage of lost posts are decreased if the "Preview" button is used before "Submit". Maybe only an issue for my pc, but throwing it out there anyway.

[a_canadian]

1. They would NEVER use aluminum in a 9mm can. It is inferior, and will erode prematurely.

That's because aluminum isn't what freeze plugs are made of, so obviously inferior. Gosh.

2. My spacing is too tight, especially the distance from muzzle to first baffle. I still need a larger blast chamber, even with my porting and it being a 9mm.

Maybe. But nah, probably don't need more blast chamber, considering the barrel porting, even using +P loads which would itself be kinda stupid considering you're after keeping things slow and quiet.

3. 10 baffles is an obnoxious amount for a can this size, Low pressure cartridges do not need more baffles as long as your baffle design is on point, and by using so many baffles it implies my baffles are sub par, but they are your standard 60 degree cone which are pretty well proven in my mind.

Nothing wrong with 10 baffles. I wouldn't go to 15, but 10 seems just fine. Might get away with 8 but I wouldn't use fewer than that, and 8 would necessitate really knowing your cone and clipping system was optimal.

4. My porting near the muzzle is apparently insulting to them, their ancestors, and their god.

I'd have to agree on this point, if you're using holes the way you've illustrated them. There's really not going to be much integrity left in the barrel with that many holes drilled so close together. I mean, it'll be pretty much one continuous jagged hole on the inside, like some sort of cave full of stalactites and stalagmites and whatever the ones coming in the from the sides might be called (is there even a name for those?). Half as many holes would be plenty. 1/3 would seem ideal. And yeah, I'd put them just as close to about 4" from the chamber as possible, in case you want to keep 115gr subsonic, or at least 124gr. Cheaper by the bucket loads seem a sensible thing to design around.

5. Porting near the muzzle will not utilize any of the expansion chamber before my baffles, and will not be advantageous for suppression.

See above answer to #4.

6. I could still use 147gr projectiles even with the porting just in front of the chamber, because my design has more back pressure than something like an MP5SD. (I did not understand this statement to be honest, but maybe I just dont understand the design well enough)

No idea here as I've no experience with anything to do with back pressure, but someone else is bound to be helpful interpreting this one.

[Kujo]

T-Rex, I have to agree with your points. That group seems moronic at best. I really appreciate all of your help so far! And as far as the forum eating posts, I have been able to save them by pushing the back button several times, and it usual comes back for me.

A_Canadian, thanks for the reply! I definitely think I'll take your recommendation on placing the ports about 4 inches up the 8 inch barrel, it seems like a happy medium. As for the amount of ports, I really was not sure how many would be needed and was fully expecting to cut down on the amount used, so I agree.

One guy went as far as to say "I have seen Sten suppressor shorter than yours use only 4 or 5 baffles and work well". For one, he must have completely missed my whole 1 stamp integral build, because i dont want a shorter suppressor. Two, I have never seen a 4 baffle suppressor but it probably doesnt work very well.

[a_canadian]

Something to bear in mind is that a lot of people's feedback regarding their experiences comes from those with tens of thousands of rounds shot unsuppressed without hearing protection, or at least inadequately worn foamy earplugs and the like. Heck, on construction sites you'd be hard pressed to find 20% of workers properly rolling the things down and inserting them deeply. Most just sort of stuff the foamy bits in part way and hope for the best. In that context you're getting the testimony of halfway deaf witnesses. Which is useless, and a bit sad. I've preserved my hearing almost religiously for most of my life (barring a very brief flirtation with punk rock bands in the mid-1980's) and to a rather considerable extent depend on my hearing to earn a living, so when I suppress even an airgun I make sure that it's really, really quiet, the most efficient thing possible. Otherwise I suffer. Suffering isn't good. You don't want to hear too much of 9mm, so make it quiet.

Have a look at this integrally suppressed commercial setup, the UDP-9i, which is regarded by some writers at least as being one of the most successful commercial versions. The guy running NFA Review Channel did a review of both long and short versions is very complementary, and he's using some nice microphone setups so you can hear how relatively quiet these things are with various loadings.
https://youtu.be/TnyNSAyOcmw

In his review there were 5 rows of 5 holes just ahead of the action, but it seems they've since decided to reduce that to either 4 or 5 rows of 3 holes. I'm guessing on the 1/8" port size, but it looks like they used 10-32" x 1/8" grub screws as optional seals on them, drilled and threaded about 1/2 way in so they bottom out when snug, which would make 1/8" ports make sense in terms of drilling then tapping above in a stepped hole. I'd concur. Thinking of going to 4 rows of 4 holes myself, to maintain better integrity of the bore, when I get around to doing something along these lines. That close to the chamber such an array would probably be enough to make all but the hottest +P 115gr rounds subsonic. Of course those would make the expansion chamber FILTHY in a very short time, so not practical in terms of maintenance, but with the grub screws you've got adjustability to suit whatever ammunition you find works well in your gun.



That's from this page:
https://angstadtarms.com/udp-9i-series/

[Kujo]

That is an interesting, but valid, point of view that I would have never thought of. I have never shot a gun suppressed before, so Im sure anyhting would sound quiet to me. Regardless, I want to build the best suppressor I possibly can.
That is also a very cool design. I would have never thought to use two tubes to create a chamber like that. While not something I would likely do to my Sten, i love the idea.
I updated my drawing one more time, this time with the ports placed 4 inches up the barrel, 3 rows of 4 ports. The ports are 1/8", and place 5/16" apart. The distance apart seems too large to me, but i figured a larger distance may be better than to close of a distance. I would think this would allow me to shoot any weight bullet i like, potentially making 124s subsonic but I would be very doubtful of that. I have never chronographed 9mm before, so im really not sure what velocities to expect out of different lengths of barrel, but I can research it.

[a_canadian]

You can always drill more holes after shooting it a bit. Material removal isn't forbidden, as I understand Form 1 rules, just adding stuff violates the spirit of the ATF stuff. So run something over the chrony then see if another ring of holes is wanted. Keeping it at 1,100fps ought to be slow enough if you don't shoot at high altitude or in winter. Below 1,000fps if you do either/both of those.

When porting, it is somewhat crucial to clean up the inside ends of the holes. Wire EDM seems to have the votes for being ideal in this regard, but if you don't have access to that, some sort of combination of a backstop for your drill and a tool for deburring that edge are in order. I've just drilled into a brass rod fairly closely fitted, then followed up with a finely coated diamond (or fluted HSS) inverted cone bit in a Dremel, going slowly and carefully to carve away a slight bevel on that inside lip. Got to mark the shaft or better still use a depth stop on it to avoid going in too far and hurting the far side of the bore, but it's not too challenging with a bit of practice on scrap. Something like this:



Of course some say a reamer is sufficient, but I don't like the idea of shaving bullets as they pass by all those ports. The remaining bore after the holes should do a decent job of correcting any stability weirdness the holes inspire, but taking shavings off the round can only harm accuracy.

[T-Rex]

. I have never chronographed 9mm before, so im really not sure what velocities to expect out of different lengths of barrel, but I can research it.

http://www.ballisticsbytheinch.com/9luger.html

You can always drill more holes after shooting it a bit.
While this is an accurate statement, he's keeping it to a single tax stamp and will need to pin/weld (or otherwise perm affix the parts) to do so. This would make it nearly impossible to keep removing the tube and further port the barrel. Not only the fabrication side, but the fact he'd have an unregistered SBR, once said tube was removed. Go ahead, but don't
When porting, it is somewhat crucial to clean up the inside ends of the holes.
I've been worried as well, but have found it to be not as big a deal. Break off what you can and run a brass brush down it a couple times. The first couple rounds will certainly clean it out. Or you can shoot some of those lapping bullets. I think drilling into the grooves can negate some of this.
followed up with a finely coated diamond (or fluted HSS) inverted cone bit in a Dremel,
We have some internal hole deburring tools. None small enough for this, but it had me thinking. They work extremely well. Here's a larger one:



and for small holes:

[fishman]

"When porting, it is somewhat crucial to clean up the inside ends of the holes."[citation needed]

[a_canadian]

Guess my lack of experience with anything as powerful as this left me with the impression that projectile integrity was important, and I certainly didn't suspect that a lead bullet would be able to clean off a hard steel lip on the inside end of a hole. My apologies for speaking from inexperience.

[Kujo]

Unfortunately with this being integral I will not be able to drill any extra holes, so I will need to get it right the first time. Aside from this, I will definitely try to deburr the holes as well as I possibly can before sending any rounds through the barrel. If I can find an inverted diamond bit to chuck up in my dremel Id use that. I also read somewhere that melting something like CerroSafe into the area you are going to drill could be helpful for minimizing the burr on the inside of the barrel, but I do not know the effectiveness of this. It certainly couldn't hurt.

[alordnapa]

You could just find some of that old Egyptian steel-jacketed, hot, hard-primered, corrosive 9mm ammo, and fire a few hundred rounds. That should stone the bore pretty well.

[ninoslavt]

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.

Are you sure about this? Buddy of mine is test shooter for PPU and he is shooting them all the time from integrally suppressed MP5s. There's only a problem if you try to use lightweight subsonic bullets (less than 140 grains)

[T-Rex]

Are you sure about this? Buddy of mine is test shooter for PPU and he is shooting them all the time from integrally suppressed MP5s. There's only a problem if you try to use lightweight subsonic bullets (less than 140 grains)

Lighter bullets (we're talking 9mm projectiles, here) travel at a greater vleocity. The barrel ports are there to drop said velocity to the subsonic range as I believe the heavier rounds were yet to be developed. Do this with an already subsonic projectile and you'll be dropping it's velocity to, IIRC, ~600-700fps. This can cause a stuck round. I know there's several Mfr's that make the MP5SD clones so I can't speak to what their barrels are ported for.

[Kujo]

The idea that moving a bullet at 600-700 fps is dangerous definitely doesn't seem crazy to me, and it is enough to make me move my porting up a little further on the barrel, I wont be losing a whole lot. It very well may work fine, but Id hate to be doing a mag dump and not realize one of the rounds didn't make out of the barrel. In any other situation a bullet moving that slowly that would be considered a grossly under powered load anyways.

[Capt. Link.]

I'm reading allot of nonsense about porting and the MP5SD.The porting position and extent was based upon making 124gr NATO standard munitions subsonic not anemic.The porting was designed to have minimal affect upon accuracy ie: shaving of bullets and jacket damage caused by other methods.The MP5SD is superbly accurate in semi-auto and capable of beer can accuracy at 100yds or more.
Lack of penetration in subsonic 124gr ammo lead to using a heavy projectile subsonic in the H&K......it was also done during WW2 for the STEN for more reliable kills.Porting position and extent is critical why would you not copy H&K porting?

[alordnapa]

I suppose the corollary of "The wisdom of crowds" is that online group members ( Fakebook) seem to lack that certain insight that makes them capable of realizing that arrogance is usually more associated with idiots than geniuses...( Except Doctor House of course) I can't really say that I have seen much of that problem here, and the range of design experience on this discussion board is absolutely amazing.

On another note, I would not consider the porting to be a pseudo muzzle brake, since it cannot redirect gasses to control muzzle climb or reduce recoil, from the inside of a tube. It's just a gas tap. I would think that it would be worth modeling the behavior of the blast chamber using a series of holes along its axis to bleed of gas more evenly after the path of the projectile. Is it safe to say that your Sten is a closed bolt semi-auto only? The suppressed Stens that I have fired ( But never owned) had a really amazing lack of "Port-Pop" due to that heavy bolt.

And speaking of tubes, apropos nothing whatsoever at all, packing an initial expansion chamber or "Blast Chamber" with copper or silver screen would make the suppressor significantly quieter than just an open expansion chamber. The gasses coming out of ports are directed like little rocket blasts into the inside walls, which creates a very perceptible mechanical noise from gas impacting on the tube walls, as well as causing a degree of heat stress and oxidation of the tube. A roll of copper mesh would diffuse the gas jets before they hit the tube wall, and dampen tube "ringing" absorb a lot of sound, protect the inner tube, and give you a nice place to add an ablative liquid coolant. ( I suppose you would be obligate to send your device to a SOT license holder to change the screen when it got dirty)

[Kujo]

I am on vacation in Michigan and a machinist cousin of mine gave me an Atlas 3950 lathe for free, so I am shipping it back home to Arizona. This definitely opens up some options for my suppressor. Any tips or videos on what kind of baffles, and how to turn them, for this idea of mine? I’d love to save the money on the internals, as well as learning to use my new lathe.