Critique the K's

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aslap
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Critique the K's

Post by aslap »

Finally assembled the Fi 22 cal suppressor and to my ears it sounds pretty good. It's on a S&W M&P 22 and the bullet hitting the target at about 15 yards is louder than the shot. I made these on the old Sears 109 lathe. I have 8 of them in a 6.8" l x 1" OD x 0.84" ID Al tube. The OAL for the K is 0.687" (with some variance due to the lathe and the machinist); OD is 0.83"; and skirt thickness on the one in the pic is 0.19" but I have a lot of variance in that particular dimension. I don't have a mill so the scoop was made with a Dremel and the hole in the cone was just done with a 1/4" drill dropped in at a slight angle. And that leads to the questions - is the hole in the cone too big and is the scoop too small. I hope you can see what needs to bee seen in the pix.

The face and the scoop
[Imageimg][/img]

Hole in the cone
Image

All of it
Image

With a ruler
Image

Thanks for any insight.
Tony S.
57fairlane
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Re: Critique the K's

Post by 57fairlane »

Yes, the scoop looks giant compared to the amount of co-axial volume.
aslap
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Re: Critique the K's

Post by aslap »

Do you mean the hole in the cone? Because I was thinking the same thing. The bore through is 0.280".

Tony S.
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Re: Critique the K's

Post by a_canadian »

I would think a 0.25" hole in the skirt would be more than enough for such small K baffles. Maybe even going a little smaller. The scoop size in the face is probably okay but it could perhaps use some refining in shape, jetting the pressure more aggressively across the bore. Remember the bore jet is still moving forward while the cross-jet is cutting across it, so there will be considerable deflection forward. Aim the scoop into the first half of the skirt hole, not into the centre or later.

The face hollow might also be a bit deeper but that's not too bad. If you want more volume, turn an angled face onto the back side of the face flat, opening out the coaxial volume considerably. That'll preserve a lot of strength nearer the waist while lightening the K mass and adding up to quite a lot of extra air volume.
Historian
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Re: Critique the K's

Post by Historian »

Aslap, compliments on what you turned out on "... old Sears 109 lathe."
A departed buddy gave me his 'Blue Beast' Dunlap and this lead me down the path of
'lathe' perdition to the Atlas 618. I still have the old 109 bed
and it is longer.

<< http://www.craftsmanshipmuseum.com/imag ... sman80.jpg >>

Many here know the Zombie murmur .. " Need bigger lathe. Need
more tooling. Cannot stop. Want 12" Atlas.".

In particular the Dunlap's 'hand crank' on the right is perfect for precision threading without
power. The control you have with it also was used for making small
clock ( not Omega or Rolex of course ) parts.

You have done the old 'door stop' proud. Congrats, Sir.

Best.
57fairlane
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Re: Critique the K's

Post by 57fairlane »

aslap wrote:Do you mean the hole in the cone? Because I was thinking the same thing. The bore through is 0.280".

Tony S.
Yes.

From looking at Ks and doing my own, you want about half that width.

Bore can be stepped down to .265 or 17/64. On form 1 stuff, I like to do a .250" blast baffle.
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Dr.K
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Re: Critique the K's

Post by Dr.K »

Looks like the scoop on the face, and the hole in the skirt do not match up. I thought they needed to be 180 degrees from each other for optimal suppression.

Seems they are canted here at about 150 degrees from each other.
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whiterussian1974
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Re: Critique the K's

Post by whiterussian1974 »

Ks usually have mouse hole in skirt @ bottom. This takes advantage of Coanda effect holding the jet against the opposite side skirt. Then the combined vector results in swirling around outside of skirt before returning to interior.

Some also place hole in top of skirt (beneath scoop) to aid with old and new air sources mixing. In this case, the bottom curved purple arrow has direction reversed.
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aslap
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Re: Critique the K's

Post by aslap »

Thanks for all of the tips!

Historian - Yep, that's the old girl. I didn't have the change gears on mine - just the pulleys and the hand crank.

I did mis-align the scoops and the cone holes. I had a hard time holding the baffle and using the Dremel to cut the scoop. I had a dater hole in the first baffle to see the blast. It was spaced 3/8" away from the muzzle.

When I drilled the holes in the cones the bit was wandering around quite a ....bit....so the holes got pretty big. I was worried about this.

The big question - if I destroy these can I start again or is it another F1 process?

Tony S.
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Bendersquint
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Re: Critique the K's

Post by Bendersquint »

aslap wrote: The big question - if I destroy these can I start again or is it another F1 process?

Tony S.
Only an 07/02 can replace the baffles without a new tax stamp for each part.

You learned alot, i would keep that can, file for a new stamp and when that new stamp comes back try something new.
aslap
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Re: Critique the K's

Post by aslap »

Bender,

I sure did learn a lot!

I can still modify these right? For example, one of the ideas was to get a more aggressive cut on the scoop. That I could do. I could probably even maybe find some way to close up the cone hole a bit. JBWeld maybe?

Thanks again for all the tips. The thing does sound pretty quiet. I'd love to compare it to a manufactured one just to hear the difference.

I'll take a pic of how I made the front of the suppressor to hold everything together since I couldn't thread with the old lathe. I think I had a pretty clever solution.

Tony S.
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Bendersquint
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Re: Critique the K's

Post by Bendersquint »

aslap wrote:Bender,

I sure did learn a lot!

I can still modify these right? For example, one of the ideas was to get a more aggressive cut on the scoop. That I could do. I could probably even maybe find some way to close up the cone hole a bit. JBWeld maybe?

Thanks again for all the tips. The thing does sound pretty quiet. I'd love to compare it to a manufactured one just to hear the difference.

I'll take a pic of how I made the front of the suppressor to hold everything together since I couldn't thread with the old lathe. I think I had a pretty clever solution.

Tony S.
You can modify those. You can always remove more metal. ATF has said in the past that ADDING anything to it is considered manufacturing, so I personally wouldn't JBWeld it.
Elkins45
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Re: Critique the K's

Post by Elkins45 »

aslap wrote: I'll take a pic of how I made the front of the suppressor to hold everything together since I couldn't thread with the old lathe. I think I had a pretty clever solution.

Tony S.
I would certainly like to see that. I have my form 1 stamp in hand, but now that its here I'm reluctant to start until I'm 100% confident of my design. I'm looking at every new source of inspiration I can find to maximize the chances of a good build.
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CMV
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Re: Critique the K's

Post by CMV »

You could always chuck a ball nose endmill into a drill press to do the scoop. Would come out better than by hand with a Dremel. Milling on a drill press isn't a good practice, but there wouldn't be high lateral stress in that operation.
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quietoldfart
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Re: Critique the K's

Post by quietoldfart »

That is what I used for cutting the vents into my K baffles; a 1/4" round-nosed end mill chucked in a cheap Chinese drill press. I set the table fairly close to the work, used a piece of the same tube as the suppressor with a slot cut out of one side and flats filed onto opposite sides as my clamping pad, and had little trouble milling so long as I proceeded slowly. Alignment was a little bit tricky but some felt tip marks prior to clamping the baffles into the vise and watching through the slot in the tube for the cone vent made it possible.
aslap
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Re: Critique the K's the tube

Post by aslap »

Ignore the craptastic finish on the tube. It was an experiment gone horribly bad.

So I had my old lathe and I couldn't cut threads so I was stuck with using taps and dies to do any threading. The lathe is obviously necessary for drilling and boring to keep holes concentric and the 1/2-28 threads for the suppressor attachment were easy. I still had no way to load things into the tube and hold things in place.

The tube
Image

The tube is 1" OD with a 0.083" wall thickness which leaves a hole that is just about the right size for a 7/8 -14 tap. The tap
Image

The trouble with this was that the hole in the tube was just big enough to let the tap drift all over the place and I was tapping crooked. I work with tubing and this is where the clever part comes in. This is a 1" Swagelok cap.
Image

Now normally a Swagelok cap is just that - a solid cap. You'll notice that my cap has a hole bored through it. The hole is just the right size to let the tap get through it. You slide the tube into the fitting, screw it down just a bit and run the tap through the hole and-voila - straight thread into the tube every time. The cap was kind enough to have a little dimple right smack in the center so anybody with a drill press can stay on center as they drill. I chucked it into the 109 and did the final boring for the tap. The fitting attached to the tube.
Image

The little piece next to the tube is called a die holder and I got that from McMaster Carr. Don't you know the hole through it is 0.250" and the threads are - you guessed it - 7/8-14.
Image

So you put your pieces in the tube and thread in the die holder like this.
Image

And if you need some extra oooomph a 1/4" hex wrench fits right in so you can tighten it against all of the parts in the can thus tightening everything up.
Image

This worked great and was easy for me without a lot of equipment.

Tony S.
aslap
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Re: Critique the K's

Post by aslap »

E45,

I lurked here for a year before I got the gumption up to get the F1 and begin asking questions. Even though what I have here may be somewhat sub-optimal, it is pretty darn quiet. Even with high velocity 22, the down range crack is the loudest thing you hear.

Tony S.
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Re: Critique the K's

Post by quietoldfart »

Nice going! I've held off buying a tap and die for my tubing - 1" OD with a 0.87" ID - as I wasn't sure it'd be practical hand-tapping the tube. But it seems likely that for my use, mostly lower velocity .22"LR and much of the blast being taken up by barrel porting with my integral design, that a metric 23mm x 1mm tap and die should work just fine. I like the idea of open-ended threading, not limiting the travel of the front cap with a flange. Although it doesn't look 'finished' the way the commercial cans and a lot of the nicer form 1 cans do, it does allow for some wear/compression of the K baffles. I recently had to add a 1mm section of tubing in front of my last K baffle for just this sort of reason. Somehow things have compressed a bit over the blast baffle and 6 K baffles such that there was a bit of play. I'd rather not hear my suppressor rattling when handling the pistol. Your threading style allows for the front cap to be tightened at will without adding anything over time, something I'm sure the Americans with their firm rules against adding elements should appreciate.
Elkins45
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Re: Critique the K's

Post by Elkins45 »

Very nice. Thanks for posting it.

Did you do your own engraving?
aslap
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Re: Critique the K's

Post by aslap »

No. I had a nice lady at work do the engraving on a machine . I tried myself with a Dremel (there I go with that again) and one of the engraving tips but it looked like absolute garbage.

Regarding my screw-in front gizmo, if you size things right, the die holder comes out flush with the end of the tube and it actually looks pretty good. Still not as good as the most of the work here but not as bad as my pix would lead one to believe.

Tony S.
Elkins45
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Re: Critique the K's

Post by Elkins45 »

Soon after I bought my lathe I discovered the joy of the will call service from Grainger. While browsing their web page I found an insanely low clearance price on 3 foot sections of 7/8-14 threaded rod. I bought several pieces and I've used some of it to make a bunch of push thru cast bullet sizing dies and M-type neck expanders in every caliber to shoot cast bullets. It seems easy enough to chop off a piece, face it and center drill to make both front and rear caps, but since 14 thread pitch is much coarser than that normally used I wonder what the downsides are?
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bakerjw
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Re: Critique the K's

Post by bakerjw »

As for using taps on anything (i.e. endcaps or tubing) for a silencer. Taps don't always run true and colinearity on a silencer is paramount.

Single point threading can be tough to learn but is the way to do it. Where a tap comes in handy it to single point cut the threads a little undersize and use a tap to finish the cutting. The single point threads will keep the tap aligned and negate the wandering.
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CThomas
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Re: Critique the K's

Post by CThomas »

Just an FYI there are a few good vids on Youtube showing how to use a handtap
on a lathe in order to get concentric threads.
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Re: Critique the K's

Post by Baffled »

Bendersquint wrote: You can modify those. You can always remove more metal. ATF has said in the past that ADDING anything to it is considered manufacturing, so I personally wouldn't JBWeld it.
I have a mental image... bear with me...

Make part of your can a simple but thick spacer, or some sort of reservoir of bulk metal of the same type as the baffles.

You've got holes too big in some baffles. You cannot replace them, or ADD anything. What do you do?

Take your "metal reservoir" piece. Saw cut, lathe cut, cold chisel, whatever, some chunks off of it. Form into TIG filler stock. Use this to weld over, build up, holes that are too small.

The net result, the can weighs exactly the same. All you've done is move metal around! :lol: Just daydreaming.
aslap
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Re: Critique the K's

Post by aslap »

I think the only way is to start over. I'll have time to learn the new 7x12 lathe. Is the electronic filing that I've heard about here available to individuals?

I do have another question. When you talk about using the ball mill and plunging into the K, do you plunge it in from the outside of the skirt into the inside or the other way around? What is the correct angle to go in?

Thanks

Tony S.
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