As I noted in another thread, I decided to grab some of these ~$10 Chinese "filter kits" to tinker with & evaluate for the Form 1 crowd.  As an SOT, I'm out nothing more than the $35.92 I spent on the 4 kits and a little bit of time, so why not?

Overview & dimensions (we're going to operate under the assumption that most of these vendors are selling the same kits, since all the descriptions & stock photos are identical)

These kits come wrapped in bubble wrap in a non-descript thin cardboard box barely larger than the tube.  The are advertised as being 6061-T6, and the way they behave when cutting supports that.  The anodizing on the samples I received is uniform with good color, but very thin, probably only a few mics.  Each tube varied a couple thou, but they average 1.054" OD and .865" ID, 5.45" long.  The threads are M24x1.25.  Each cap will add 1/4" to the OAL, making the grand total 5.95" with the caps tight to the tube.  So, practically speaking, it will yield a 1-1/16 x 6" suppressor weighing about 4-1/2 ounces.  

The thread tenons are 1/2" long and have a ~.110" undercut behind the threads.  Threads are clean, properly chamfered, and have a looser end of class 2 fit in the tubes.  The ID of the front cap is .750", and it's counterbored .65", so the thickness at the front is .1".  The mount is 1/2-28, also a class 2 fit, though on the tighter side.  The mount is counterbored 1/4" on the inside, so there is 1/2" of 1/2-28 female thread.

The spacer is .855" OD, .75" ID and 1-1/4" long.

Each cup, of which there are 7, is .855"-.857" OD with a .46" long skirt. The cones are 60°, have a 1/8" register at the base and are truncated with face diameter of ~.44".  They are center marked on the outside.  Skirt thickness is about .055", cone thickness about .065".  Skirt IDs hover around .750, while the registers are about .740", so they are not a tight fit to one another; you will need an alignment tool to keep them from twisting when you tighten the caps

All edges are chamfered, cleanly but with minor variation.


Making the filter kits into suppressors

I did them a few different ways to see what all can be gotten away with.  I bored all the apertures to .280".  I metered with just holes, with double radius clips .105" wide and .115" deep, with the insides of the cones bored to get rid of the tunnels, and in both 7 cone "stock" configuration as well as one I modified to have 12 cones with a much shorter spacer.

I tested only with CCI Standard Velocity ammo, hosts were my Savage Mk II with a 16" barrel and a Beretta Model 71.  

My control suppressors were the TBAC Takedown .22 and my Ocelot M.  The TD22 averaged 114.6 on rifle, 118.7 on handgun.  My Ocelot averaged 115.1 rifle, 118.6 handgun  

Drilled only yielded poor results, giving 124.1 on rifle and 133.2 on handgun, with FRP pushing 140.

Clipped gave massive improvement, 119.6 on rifle and 128 on handgun, but still big FRP



Using a countersink/starter drill to bore from the inside and create a sharp transition further improved the reduction, giving 115.8 on rifle and 126.3 on handgun.  Still had nasty FRP on pistol, though

 



Going to 12 clipped & inside counterbored baffles with the spacer shortened to .500" made little difference on rifle (115.7), but made a huge improvement on the handguns, bringing the average down to 121.2.  FRP was still there but much less.  The extra cones added 1/2 ounce.



I did try the 12 baffle version on my CMR30 SBR with 10" barrel, and though I didn't meter it, I would guess high 130 dBs.  It didn't hurt my ears, but it was loud.

As a last step, since someone in the other thread mentioned 9mm use, I bored one of the stacks & caps out to .410" with shallow double radius clips of 3/32 radius and gave it a go on the RP9 with 147 gr/990 FPS loads.



Dry, it was loud, definitely over 140.  Took the edge off, but it would leave your ears ringing indoors for sure.  With ablative, however (white lithium is what I used), it was fairly pleasant.  I didn't meter it since I'd already put that away, but my calibrated ear says it was in the 134-136 range, on par with a lot of full size .45 cans running 230 gr. ball without ablative.  4.5 oz is teetering on the heavy side of being able to run boosterless, though.  While a Beretta wouldn't complain, I had to have a very firm grip on the RP9 for it to cycle.  I consider 4 oz to be about the limit for boosterless cans on Browning style short recoil 9mms.  How long an all-6061 can would hold up on a 9mm pistol is another matter, but it took a few rounds without a problem.

In summary, while they're certainly not on par with quality commercial cans or top-tier F1 builds, these can be made to perform decent on handguns and very well on rifles.  Due to the alloy, I wouldn't recommend them for heavy use on anything other than .22 LR, but in that role, they are just fine.  When one considers that you can have a decent performing (if not a tad large) rimfire can for ~$220 with 2 kits and tax stamp and maybe up to a couple hours of your time, depending on skills & equipment, they're worth a look.

Thank You for your work.

Thanks for the write-up. Any suggestions on clipping for someone that only has a drillpress/hand drill/Dremel vs a milling machine?

Nice write up. Interesting results amongst the mods.

Interesting review.  Thanks very much for taking the time to produce it.

………….

Thank you sir! Great work.

Thank you for doing this. I had been wondering how these cheap kits would perform. Didn’t want to pay for a stamp just to have this be very underwhelming.

You can certainly get it done with a Dremel, and cleanly if you have a steady hand and take your time.

Excellent- thank you.

Might be worth doing a cheap .22 rifle setup for plinking use on the cheap!

Nice work, very interesting.

In the 12 cone 22, since you already tightened up the spacing so much, is there any other way to reduce FRP?

Real curious how well these would work on a .25 and .32acp.

I've been doing some reading and making plans to get into Form1's so just speculating and curious.

Did you line up the clipped areas of the baffles when installing? And would a small chamber at the muzzle end
help to reduce FRP?
Thanks for the time and effort you put into this, It is greatly appreciated!

tagged, thanks for the write up

Not really, not without a different cone profile.  It wasn't too bad on the 12 baffle version, though.  Horrible on the 7 baffle ones on handguns with the long spacer.

.25 is rather poppy compared to .22 LR subs, more along the lines of mini mags, stingers, yellow jackets or other "hot" .22 LR ammo.  Likewise .32 auto is higher pressure and more powder than either.  I think hearing safe is possible, but not really quiet without ablatives unless you go the extra cone route.  Still couldn't say for sure, of course.  Maybe I'll order a couple more at some point and test that.

Yes, I aligned them with a piece of 316L 1/16 x 3/8 flat stock

Reducing FRP without ablatives is achieved with good baffle design and minimal blast chamber; a chamber at the front wouldn't help that.

I've been toying with the idea of a form 1 since I read the electronic version is going through so quickly.  Up till now it hasn't been the $200 it's been the time that the can and the money is in jail that kept me from doing it. For less than $50 a month  plus the stamp I might give it a try.

Nice write up.

I have considered numerous times to do a F1 build but lack the tools and skills.

But something like this I think is within my grasp.

How about a 17hmr?

That's gonna beat the shit out of a 6061 aluminum blast baffle in short order.

Pick up one of the SS kits for $14 for .17 HMR.  Well, I'll see if they are SS.

Where do you find these filters?

Ebay

It looks like a lot of the cheapest kits from China got deleted. They even show deleted in my order history so you can't see them.  I just ordered them less than a month ago and the wife said they are at the house.

I did order a larger k baffle style kit today. Pricing was in Australian but that may be cuz I'm in Kurdistan with weird internet

So a few manf. questions

- do the clips need to be lined up down the line or does it matter? You mentioned using flat stock to keep things indexed so I assume the clips need to be in line with each other?

- what do you mean by countersinking the hole? Completely lost there

I purchased a "Upgraded Stainless Steel" version of this filter.  Went to check on it today and even in my purchase history, it shows that the listing is now an electric screw driver.  But, if I click on View Transaction, it shows the filter.  We'll see.

If you look at the first picture, you can see that the holes drilled into the cones are straight up and down.

Second picture shows them angled at the same angle as the coned portion.

Thank you that makes sense! Damn, little changes like that make a difference? Damn.....

Thanks for doing the tests for us! I've always wondered about these things, since I can't even get the raw materials for double their price, let along the hours I'd put into all of the pieces. Not to mention I haven't tried threading yet...

I just ordered a couple kits. $16 ttl with free shipping.

Absolutely.  That's why there's really no useful formula for building these things and getting optimal performance.  Changes in baffle spacing, blast chamber size, cone angle, cone shoulder, clip style & size can have a significant impact on performance, both suppression and influence on bullet flight.   Some designs are more forgiving than others, though, which is why smooth 60° cones are popular with the F1 crowd; they tend to perform pretty well with a wide range of pressures & volumes.

Aliexpress

These are nearly identical to the form1builder kits. Rather than more baffles, I had success in getting rid of every other baffle and machining them into spacers. Give that a try and see if it helps. Otherwise the cans develop WAY too much back pressure from loss of internal volume due to the thick aluminum skirts

Has anyone tried the 6" x 1.365" OD, monocore with 7 dividers, filter kits that are available? or would the same size tube with clipped cones be more effective?
I'm considering a Form 1 can for an AR9 pistol with a 7.5" barrel. Would an 8" tube provide any advantages?

This is a very thought provoking thread, Thanks.

Interesting results.  I am debating making a few k-baffles on the lathe at work for when I build mine. Anyone have details on what k-baffles are best for?  Subsonic?  Large bore?  Etc...

I've heard how great they work. But not in what circumstances

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Has anyone tried one of these? After getting your F1 or course.

It'll hold up, and work surprisingly well.

You make this statement based on a sample size and round count of what?

17 HMR is a high velocity number.  The powder charge may be fairly small, but it's substantially more than .22 LR.  It also runs at higher chamber pressures than .22 LR, and the tiny bore does not attenuate the pressure as much (Boyle's law; .172 cal bores will retain 68% more pressure than .223" cal in a given length).  There's also a lot more heat input with .22 WMR and .17 HMR, which will start to erode even 7075 blast baffles with decent anodizing pretty quickly.  7075-T6 has twice the strength and is 50% stronger than 6061-T6 and, as I noted, the anodizing on these chicom parts is super thin, offering no mechanical protection.

There's a reason all-aluminum rimfire cans are rated as .22 LR only.   I stand by my statement.

I'd like to try one of those.  There are "reasons" I"m not willing to order one.  

If you have a F1 in hand what can they say?

From what I see I think they're technically a suppressor as is.   Most of those are coming w/ two end caps.  One w/o a hole and one that is just a ring.  You could screw it on and shoot it immediately.   Combine that w/ the monocore baffle stack and the SIG ruling on their brake.  Not willing to take the risk.

And if you have an approved Form 1, not an issue.

I packed some of the excessive space in my F1 with steel wool and it seems to have reduced frp and possibly successive round dB. I have no meter so just using mk1 tinnitus.  Also I made a cone out of sheet metal to fit on/in the exit cap where there’s that massive void between the last cone/spacer and the actual exit hole. Unknown effect but the logic of it made sense to me.

You know steel wool is flammable right?  Is it still steel wool in there or a pile of iron oxide now?

Hey ECCO,  would you be down with us pitching in some cash or sending some kits to you directly just so you can do more experimentation?  
At the prices of the kits, I'd have no problem sending a few for you to test destructively or not.  Maybe even one of those monocore ones.

I’ve run a few mags through it with a 22lr and it’s fine. I was actually looking for the copper version of it but I didn’t have any on hand and had forgotten to buy some. I *think* that stuff is fairly ok to use.  As for using steel wool, I’m pretty sure the Soviet suppressors during a good chunk of the Cold War used it (at least for low powered rounds). They weren’t terribly great nor have a long lifespan, but they were essentially just using it without baffles which would destroy it fairly quickly. Having the steel wool passed the blast chamber seems to hold up fairly well on mine.

Are you sure?   From what I see that would be like ordering a suppressor from an established mfr w/ the understanding I have a form 1 in hand to "make" it as soon as I got it.    I don't see how that's legal.  I'd like it to be, but I wouldn't take the chance.  The ones I've seen have a threaded collar, a cap you can drill, and the "brake"/baffle stack.   Unless I'm missing something you could literally screw it on a rifle and shoot as soon as you got it w/o doing anything.   I don't see how a F1 is going to work w/ that.

This is the style I'm talking about.

Attached File

Without the exit hole, it is fine.

Sure.  Like I said, my time investment in poking a few holes in aluminum bits is minimal.  It takes me longer to do the engraving and efile F2 than to make these things functional cans.

If that's something you want to do, I'd say the best bet would be to order it yourself, examine it when you get it and sketch or describe what sort of alterations you'd like to see, then pop in in a first class mail parcel for a couple bucks.

As for destructive testing, I'm game up to a point, but I won't risk hosts or my safety, so don't ask me to screw a 6061 rimfire thing on a 5.56 SBR or my .375 RUM.  I can tell you what will happen without the molten shrapnel show!  And we might have to talk about covering ammo.  I'll be happy to see how many .22 WMR rounds they'll stand up to or somesuch, but my means are a little meager to foot the bill on hundreds or thousands of rounds just for the sake of trying to burn down little aluminum cans.

This just made me imagine one of those little hand crank 22 Gatling guns with a suppressor on each barrel spinning around.

Incidentally the end caps in these 1x6 kits are a perfect fit for 3/4" drill bushings, and 3/4" wipes.

completely understandable. I will see what I can provide and what ideas we can come up with. Make this an ongoing experiment. I won't be able to ship any home and then t you at the moment, as I'm overseas and constantly traveling (plus Iraqi customs is much more strict about "war material" being shipped). And for destructive testing I was thinking more along the lines of torture testing or seeing how one of these looks after a hundred rounds of 9mm or whatever. So I (or "we" if anyone else joins in) could definitely make that happen

@Sixtysixdeuce

IM sent if you will