Form 1 design for an FN1900 in .32 ACP

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TheATeam76
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Form 1 design for an FN1900 in .32 ACP

Post by TheATeam76 »

Hey guys! I'm new here, and I wanted some critique on my (first ever) form 1 design before I commit to it. The host weapon is going to be my FN1900 (.32 ACP) with threaded barrel that I did all the work on myself. I've gleaned a lot of my general design principles from lurking on this forum, but most of the specifics to the can I came up with by mostly "winging it". I went with a 1.25" OD tube in large part because I felt that the diameter would complement the aesthetic of the pistol well. It is a tad over 6" in length, which I again felt would make for a good aesthetic and also be enough length for effective suppression without becoming super unwieldy. But I haven't filed the form 1 yet, so if a different length woud be more suitable, I can still change it.

The tube and endcaps are both 4130, as I wanted something weldable since I plan to weld it together. I will not be shooting non jacketed lead projectiles through it, and it is a fixed barrel blowback design not necessitating a booster, so I determined the benefit of being able to dissassemble for cleaning negligible. Please correct me if I am mistaken in thinking this.

The blast baffle is 17-4, and the subsequent baffles (and blast baffle spacer) are 7075-T6. I designed them all with a .060" skirt thickness, but from what I've read since, I can apparently get by with a lot less? More research is needed. They all have a .400" through bore. Not sure if that is adequate or overkill for a .32acp.

The ports/clips/etc. in all the baffles I kinda just made up as I went along based on browsing pictures of various K baffles. Any input on whether I'm on the right track or not would be appreciated. If anybody wants to get really in-depth with the specifics (if they matter), I'll make detailed drawings of all the components.

Another design feature I've tried to implent has to do with the direct thread attachment. I has a counterbore in the threads that allows a Viton o-ring to set inside it and have an interference fit with the barrel right after the threads. Hopefully this will keep it from backing off when firing. I can post a detailed view if there's interest.

Solidworks tells me that the weight is 9.58oz in weight, and the center of gravity is directly in front of the blast baffle. No idea if that is relatively good or bad.

Thanks in advance for any feedback.

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Hatchetjoe
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Re: Form 1 design for an FN1900 in .32 ACP

Post by Hatchetjoe »

A bore of .375" would be fine, the cutouts at the front of the K baffle will be detrimental to sound. The blast chamber is probably twice the length it needs to be and will increase FRP. Don't eliminate the blast chamber completely as that may cause lots of port noise on a blow back. I can't tell for sure but the baffles look long are they 60 degrees? I would probably go with two steel baffles. And reduce their wall thickness to 0.040". Just my $0.02.
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Capt. Link.
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Re: Form 1 design for an FN1900 in .32 ACP

Post by Capt. Link. »

TheATeam76 wrote: Sat Jun 13, 2020 1:22 am
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Classic firearms are very special to me.They exhibit not only artistic value but mechanical genius in ones hand.Period styled accessories would be mandatory to complement this fine weapon in my opinion.
A near historically accurate suppressor would call for blued steel of a eccentric nature.This would allow the use of sights which was popular at that time period.A wood presentation box to display the pistol and suppressor would be a nice touch.

Simple slant baffles welded into a blued tube would be effective and robust.
The threaded muzzle must have either a true face or a shoulder for the suppressor to seat upon.A o-ring is inferior to a well machined cap and torque shoulder.
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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T-Rex
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Re: Form 1 design for an FN1900 in .32 ACP

Post by T-Rex »

A lot of your design features are ancient. Drop the perforated blast baffle. A single port is all that's needed. Ditch the mousehole (the cut at the cone's base). As said, blast spacer is huge. I'd probably put the first baffle 1/4" from muzzle.

Personally, 'd just fill the volume with cones, but K's can work, too. I just don't think 4 K's will do as good as however many cones you could stuff in there (probably ~8).
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Re: Form 1 design for an FN1900 in .32 ACP

Post by ECCO Machine »

T-Rex wrote: Sun Jun 14, 2020 1:47 pmPersonally, 'd just fill the volume with cones, but K's can work, too. I just don't think 4 K's will do as good as however many cones you could stuff in there (probably ~8).
This.

My .32 ACP pattern is a 1.125 x 6.5 .035 wall Ti tube with one 17-4 conical baffle and ten anodized 7075-T651 conical baffles.
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TheATeam76
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Re: Form 1 design for an FN1900 in .32 ACP

Post by TheATeam76 »

Capt. Link. wrote: Sun Jun 14, 2020 10:39 am Classic firearms are very special to me.They exhibit not only artistic value but mechanical genius in ones hand.Period styled accessories would be mandatory to complement this fine weapon in my opinion.
A near historically accurate suppressor would call for blued steel of a eccentric nature.This would allow the use of sights which was popular at that time period.A wood presentation box to display the pistol and suppressor would be a nice touch.

Simple slant baffles welded into a blued tube would be effective and robust.
The threaded muzzle must have either a true face or a shoulder for the suppressor to seat upon.A o-ring is inferior to a well machined cap and torque shoulder.
I'm definitely going for an old school look with this. That's why I chose a 4130 steel tube as opposed to aluminum or titanium, so that I could refinish the tube to match the gun. We're absolutely on the same page! As for eccentricity, the cool thing about the FN1900 is that the barrel is underneath the recoil spring, making for a tall height over bore. According to my measurements you could actually go up to 1.5" in diameter with the can and not have to make it eccentric to prevent blocking the sights. That was why I thought it would be a perfect suppressor host, on top of basicially any factory .32 ACP load already being subsonic. Hadn't thought of a presentation box. Great idea!

The muzzle has a true face and the cap is designed to index off of it. To be clear, the o-ring is only providing additional friction to keep it from coming loose, not controlling alignment. What do you mean by torque shoulder? A cursory web search came up with a bunch of swimming and oil drilling industry results. If you have a good resource on the matter I would love to read further.

By the sounds of it, my baffle design specifically need some work. But generally speaking, what plays into the desicion to go with Ks, cones, or slant washers? I'm trying to learn here, but the impression I had going into this was that Ks (obviously better designed ones than mine) were superior in suppression, just slightly heavier and more difficult to machine. Are cones or slant washers more effective in this context becasue of the limited space in this design, or are they more effective in general? If there's a good resource for reading up on the correct application and pros/cons of different baffle styles, I'd love to learn more. Nothing became immediately apparent from perusing the forum.

As a whole, thanks to all of you for your thoughtful input. I'll make a couple different revised designs based on your suggestions and post them up to see what you all think. I'll make a detailed view of my o-ring retention arrangement, hopefully that will clarify what I'm trying to do with that as well.
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Re: Form 1 design for an FN1900 in .32 ACP

Post by ECCO Machine »

TheATeam76 wrote: Mon Jun 15, 2020 7:26 am By the sounds of it, my baffle design specifically need some work. But generally speaking, what plays into the desicion to go with Ks, cones, or slant washers? I'm trying to learn here, but the impression I had going into this was that Ks (obviously better designed ones than mine) were superior in suppression, just slightly heavier and more difficult to machine.
I have never found a K baffle design (mine or anyone else's) that suppressed better than properly designed & spaced conical (or sometimes radial) baffles in any application.

I've done cans with K baffles similar to your proposed design, as well as many others with many variations on angle, waist size, port type, scoop type, etc. Some were pretty good, but tightly spaced conical baffles still sounded and metered better.

This is my .32 ACP design:

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Larger caliber designs are basically the same, just scaled up.

For supersonic rifle rounds, I still use cones, but generally 50° rather than 60°, and a mix of smooth & stepped with progressive spacing:

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TheATeam76
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Re: Form 1 design for an FN1900 in .32 ACP

Post by TheATeam76 »

EDIT: Got the photos to display, but hadn't realized that Solidworks cropped some of them weird. But oh, well.

Made another attempt. Changes made:

1. Made overall length a bit longer, at 7.375"
2. Switched to 60° cone baffles instead of Ks
3. Thru bore reduced from .400" to .375"
4. Blast spacer shortened to place tip of cone .25" from muzzle
5. First two baffles are 17-4 stainless instead of only the first one
6. All baffle wall thicknesses are .040" instead of .060"

My questions:

1. Cone spacing is .338". Is that too close? Too far? Is there a good guideline or rule to go by? I managed to fit 17 cones in there like this.
2. Am I reaching diminishing returns in terms of overall length versus suppression? Or can I shorten it a bit without a noticeable difference?
3. Solidworks says weight is approximately .731lb or 11.69 ounces. That's an ounce or two more than many of the 9mm cans out there that I've seen. Would this feel way too heavy to use? Or would it feel like a "good" heavy in the same way that the all-steel pistol itself has the right amount of heft to it? I may shorten it a bit to reduce weight, but I don't really have a good frame of reference. Maybe I'll machine some weighted contraption that I can thread onto the barrel to put small weights on to get an idea of what it would feel like.

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This is my o-ring friction retention idea. The can still indexes off the muzzle, the o-ring just adds friction to the outside of the barrel to prevent unscrewing. Hopefully that clarifies what I'm trying to do. If it still seems like a bad idea, I don't have a problem with changing it.
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This is my off the cuff attempt at drawing the clip. No idea what I'm doing, just copying from pictures. How important is clocking the clips so that they're all in line? ECCO Machine, in your pistol can the baffles seem to snap together to keep them aligned, but in the pic you posted of the rifle suppressor internals, they do not. Is there a specific reason for that?
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And a rudimenatary drawing of the baffle in general:
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T-Rex
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Re: Form 1 design for an FN1900 in .32 ACP

Post by T-Rex »

1.25x6 should be plenty
No need for any o-rings
I prefer not to space baffles near projectile diameter.
See how many cones you can get in a 6" tube @ ~.375in
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Re: Form 1 design for an FN1900 in .32 ACP

Post by ECCO Machine »

TheATeam76 wrote: Mon Jun 15, 2020 7:31 pm ECCO Machine, in your pistol can the baffles seem to snap together to keep them aligned, but in the pic you posted of the rifle suppressor internals, they do not. Is there a specific reason for that?
The rifle can pictured is pre-assembly; it is a fully welded tubeless suppressor. The clips are aligned prior to welding.

I do put indexing features on serviceable stacks.
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TheATeam76
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Re: Form 1 design for an FN1900 in .32 ACP

Post by TheATeam76 »

Took another go at it based on feedback. Changes made:

1. Length reduced to just over 6".
2. Baffle spacing increased to .375" from .338"

New weight is 10.2oz. With the reduced length and increased baffle spacing I still get twelve cones in there. I figure that ain't bad at all.

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TheATeam76
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Re: Form 1 design for an FN1900 in .32 ACP

Post by TheATeam76 »

Finally got my form 1 back on this one. I went with a different style of clip on the baffles than what I originally had planned. Based mostly on internet anecdotes, some from this site, saying that it is "better". I figured I'd try it. Other than that, it's pretty much the same as the designed I posted above.

I've already test fired it. It works excellently! Totally hearing safe, and has an awesome tone. It actually makes a sort of Hollywood-like "phew" sound which to me is both entertaining and hilarious. Another test that I did was to shoot it from inside a 40ft CONEX container out the door from about 20ft inside. The brass clanging against the wall of the container was louder than the muzzle report! Still totally hearing safe in confined space, which makes me most pleased.

My o-ring friction retention system also worked perfectly. I fired 100 rounds through it without it coming loose at all.

I finished the can with John Norrell's Moly Resin, which is the same finish as the FN1900 I have it attached to. I like it because it is extremely durable, and heat/corrosion resistant much like Cerakote. Difference being that it has a lower NIR signature than Cerakote, making it better for those sneaky night ops.

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Tango2521
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Re: Form 1 design for an FN1900 in .32 ACP

Post by Tango2521 »

That’s a nice job. Congrats!
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Re: Form 1 design for an FN1900 in .32 ACP

Post by Historian »

Add my 'Standing-O's' to your well designed and executed metal art.
Clean, minimalist, and efficient as you report.

Thank you for the reference to John Morrell's Moly Resin product,
First time I have heard of it.

Again, thank you for brightening up the morning.


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Capt. Link.
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Re: Form 1 design for an FN1900 in .32 ACP

Post by Capt. Link. »

Well done sir !
I could see this as issue for spooks of ww2. The welrod may have never been developed.
-CL
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TheATeam76
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Re: Form 1 design for an FN1900 in .32 ACP

Post by TheATeam76 »

Thank you for your kind words, everyone. I appreciate all of the helpful tips and advice you all provided along the way.

This pistol project isn't quite finished, however. What's left to do? Extended magazines! I'm gonna take a crack at stamping some of my own magazines, and forming some of my own mag springs. I figure that will complete the look. That project is a ways off, but I'll be sure to report back here on how it goes.
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