Some k baffle questions

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vaeevictiss
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Some k baffle questions

Post by vaeevictiss »

Im working on a 9mm Subsonic can (continued from my other post) and i just have some questions on the k baffles.

1. I'm hoping i can explain this well without an illustration or making a baffle and cutting it in half, but imagine a baffle cut in half. The standard "groove" that is in the top around the bore is normally cut with a rounded cutter, so with a baffle cut in half it would have a "u" shape. How would a different shape work? I'm thinking like a trapezoidal shape like this:

|\___/ \___/|

2. On the topic of dater holes, i get that only the blast baffle needs one, but is one all that's needed? Ive seen a couple pictures of k's people have made with 2. 180 degrees from each other.

3. What is the proper way to cut the port? I've seen two ways referenced. One is to put the baffle in the vice on the mill at an angle and basically cut the notch in the cone and continue through to cut the hole in the skirt with a flat end mill. The other way I've seen is to put the baffle in the vice straight up and down, and use a round end mill to cut the notch in the cone. Then, flip the baffle over and cut the skirt on the opposite side of the bore.

4. Is the rear of the face supposed to have a taper to it or can it be flat?

Thanks for any help.
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CMV
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Re: Some k baffle questions

Post by CMV »

A lot has to do with the angles you are using. If you look at different K baffles you will see the bottom/face machined differently. I have done them like this before & they work well - more like the one on the right using a tool ground as pictured.

But I did 'clicky cones' for my 9mm & not K's so don't know about that application.

Image
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quietoldfart
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Re: Some k baffle questions

Post by quietoldfart »

Someone on here, CurtisTactical if memory serves but perhaps not him, actually says that a trapezoidal trough performs a but better then a U-shaped or heli-toroidal channel. I've found the rounded channel to perform extremely well,ebsides being easy to clean, so haven't yet tried the flat-bottomed version.

I've tried two holes in the blast baffle, but went back to a single hole. Actually using a small hole at 180° from the first one, in the face of the second baffle, seems to be better than just one in the first baffle and better than 2 in the first baffle by a fair margin.

On the ports, again I'll cite CurtisTactical, as he's said quite clearly that a plunge cut parallel to the bore performs better. Unless that was Gunny50... old memory gets fuzzy. I've done both angles with a ball-end mill matching the bore size, and found no discernible difference. The resulting profile of the cuts aren't all that different anyway. I expect it's simply easier to do them parallel to the bore.

Not sure what's meant by the 'rear of the face.' If you mean the face of the entry point of the projectile, the cone at the inner circle of the K face, then I'd suggest as sharp as you like. I tried a set of K baffles with a knife-sharp edge on that circle, recorded the numbers and my impressions, then shaved off the faces to leave about a 3mm wide flat at the bore entry and tested again. It got louder. About 2 to 3dB.

Bearing in mind, my experience with noise suppression is exclusively in PCP airguns and .22lr pistols and rifles, so may be only somewhat relevant for your 9mm application.
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Re: Some k baffle questions

Post by vaeevictiss »

CMV wrote:A lot has to do with the angles you are using. If you look at different K baffles you will see the bottom/face machined differently. I have done them like this before & they work well - more like the one on the right using a tool ground as pictured.

But I did 'clicky cones' for my 9mm & not K's so don't know about that application.
Cmv, i think i saw you post this on another thread

Image

couldn't both operations be done with a ball end mill? Or should you only cut out to the back of the face. I figured you would want to go deeper into it so you also have a round indention to match the one cut in operation 1.
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CMV
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Re: Some k baffle questions

Post by CMV »

I don't see why not. That's just the way I do it & leave the spot I do w/ the square endmill flat at the bottom of the cut.

But that pic shows how the tool in my 1st post can cut the face. Square to the bore & then a crescent-like channel
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vaeevictiss
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Re: Some k baffle questions

Post by vaeevictiss »

Do you find a difference when that center is cut square to the bore vs a mini cone?
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Re: Some k baffle questions

Post by vaeevictiss »

Also, what size expansion chamber would be recommended? Again, this will be Subsonic 9mm only. I'm kinda confused because the general rule of thumb is a smaller blast chamber will have less FRP. This is true with my trident as looking inside the blast chamber doesn't seem big at all (granted it has omegas). But then you see people building 9mm k baffle cans with either long blast spacers or reflex chambers and they claim that they are extremely quiet.

I know in my rifle cans i had rather large blast chambers and they sound great but it seems its totally different with pistol calibers and k baffles.
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Re: Some k baffle questions

Post by CMV »

I can't say "I notice a difference" because I'd have to make two absolutely identical except that one feature and then compare. I just did it once because it looked like I could cut that channel deeper and still have a curved surface. That worked so I stuck with it. Whether that matters or not, I couldn't tell you, but I've done a few this way and they work well.

I might be doing it wrong, but anything I make using K's has virtually no blast chamber. I want that first K close to the muzzle - maybe ~300"
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vaeevictiss
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Re: Some k baffle questions

Post by vaeevictiss »

Damn that's really close. Is there a sweet spot? By that i mean will you get FRP with a blast chamber too long OR too short?

Seems like there's a lot of trial and error involved and we are not allowed to do trial and error. I got a buddy who owns a gun shop and he's an sot. Maybe he'll let me use his shop to try a couple things... If that's something i can do.
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Re: Some k baffle questions

Post by a_canadian »

You might try just cutting acouple of short spacer tubes , say 0.300" and 0.150". That would give you the possibility of testing slavers and baffles in different arrangements. No spare parts. No laws violated. Just test at 0.150", then at 0.300", thn if neither is quite what you want test again with both spacers for 0.450" blast volume. Whichever spacer isn't wanted for the blast chamber gets shuffled to somewhere further down the baffle stack. This actually presents an interesting bonus - Capt Link has talked a bit about rendering an uneven baffle stack to break harmonic coupling or somesuch, the tendency for waveforms to propagate in symmetrical environments. By putting a small spacer somewhere midway down the K baffle row or playing around with its location you may find an improvement in suppression efficiency. In any case, such a pair of spacers of whatever lengths you wish offer three distinctly different blast chamber volumes, while remaining within the intent of the rules around a fixed set of parts.
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Re: Some k baffle questions

Post by vaeevictiss »

Yea that's not a bad idea and a good way to find tune.

Back to the expansion chamber size, check out the octane 9:

Image

now they don't use k's, but from the looks of it, nearly 1/3 of that can is the expansion chamber. 1/3 is a number that seems to float around here a lot. I've never heard the octane (wish i got one instead of my trident) but practically all of silencercos cans are pretty damn quiet.

Edit: now that I'm looking, i cant find an octane with a baffle stack like this. All the ones in seeing don't use omegas. Weird
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Re: Some k baffle questions

Post by T-Rex »

You're not factoring that a good majority of the space houses the booster.
Find a pic of a piston, scale both pics, and you'll have an accurate model of the design.
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vaeevictiss
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Re: Some k baffle questions

Post by vaeevictiss »

hmm good point. What if you are using the can without a booster like on a subgun? Or is this the part where people say some cans work better than others on a rifle vs pistol?
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