My hybrid SDTA design.

[whiterussian1974]

Here are the plans using SDTA sourced parts.
The far endcap is based on Gunny50's vented design.
And the slits in the barrel are EDMed to vent gas into coaxial chambers and sequester off boreline until the later chambers begin to normalize.

Save the .bmp and open and it gives ruler measurements. 12" ttl. .5" endcaps. (3) 2" 304SS spacer tubes w washers separating them. 2.375" muzzlebrake w 2" of ports venting into chamber. Then, (5) machined 60* cones at equal spacing followed by (3) more @ closer spacing. All cones to feature (3) .250" notches in mouth @ 60* offset.
Finally, the endcap w 3 versions shown. The 1st is 45* slant w grommet collar tacked to cross members.
The 2nd is (2) layers of .125" tubes drilled into solid barstock. Each layer offset 22.5* from the other.
The 3rd, simply (1) layer of .125-.250" vent tubes to spread exhaust over a larger surface area, minimizing compression disturbance at bore exit.

I color-coded the parts to make ID easier.
Thanks for any comment/suggestions.

[whiterussian1974]

Far endcap kinda like this:

Just 1 section used. This image is only for visualization of far endcap.

[L1A1Rocker]

I don't recall seeing a vented end cap like that before. What are the advantages?

[c5_nc]

Since there is very little volume in the last chamber I doubt the venting would make a noticeable difference either way (better or worse). I didn't notice any SDTA parts in the diagram am I missing something? The one I would note is i thing your size is a little large and you may regret doing that. I build a 8.8" and 7.6" form 1 can recently and they performed much better than expected.

[whiterussian1974]

Updated Pic:

After posting I thought, "Maybe I wasn't clear w endcap options." So, I drew up some alternatives for you to comment upon.
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L1A1: The advantage of vented endcap is to smooth the sudden concussion wave of gas compressing the outside air. Like a belly flop instead of a graceful hands first.
Or maybe better explained by formula: (1) .375^2Pi @ 100% vs (1) .375^2Pi @ 35% + [(8) .250^2Pi @ 8%] + [1% waste heat] - [5%? wavefront interference.]
So it sounds more like a leaky tire instead of a burst balloon. Or image speaking w a megaphone vs unaided.

The 1-point exhaust endcap acts as a horn. Venting it reduces the initial and subsequent shock waves.
https://en.wikipedia.org/wiki/Shock_wave

Like the difference b/t throwing a handful of sand vs a rock. The sand is many small pieces that dissipate quickly. The rock, one solid mass w minimal Surface Drag to Volume and Mass ratio.
"This will disperse the shock wave at some places and focus it at others... the shock wave energy density will decrease beyond expected values based on uniform geometry (1/r^2 falloff for weak shock or acoustic waves, as expected at large distances)."
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c5_nc: Yes. The Ideal Gas Laws work in the early sections; so the endcap is just for dissipation of blast wave. Nasa has some wonderful tools and explanations on their public site. http://www.grc.nasa.gov/WWW/K-12/Underg ... /index.htm

The outer tube, spacer sections, muzzlebrake and 3-4 freeze plugs are sourced from SDTA. Of course, that's just the option that I'm leaning toward in order to save my labor.
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ETC: corrected scripting changes to 'img' links that were shifted during update.

[whiterussian1974]

I'm leaning toward the left sectioned option. Siphoning off gas and expanding from .125" inlet to .250" outlet. This should further expand and slow the exhaust.
The upper-left pic of section 2 doesn't offer sufficient obstructive surface to reflect waves or offer choked flow. So I'm against it. Just posted for comparison.
Upper-right offers good expansion volume, but little obstruction. Still probably not the best option.
The bottom pics I should have clarified. The inlets would be .250" and outlets ~.375". They would still require the 2nd pic from Section 1 as the outer endcap surface to provide choked flow. But they differ from the cross-section of section 1 in that they offer added expansion volume and a choked exhaust as opposed to an expanding exhaust outlet.
Just perhaps a modest improvement in performance?

If you haven't viewed my "Does anyone have ideas for radical designs?" viewtopic.php?f=10&t=123579&p=909419&hi ... al#p909419 please visit it. And please add any wild "blue Sky" ideas that you've ever thought of. Maybe it will percolate in others' minds and develop into "the next great thing."
And here is Gunny50's design. He uses it in production of commercial cans in Europe.

[T-Rex]

Oddly enough, at the present, I'm designing something remarkably similar.

The preliminaries





The rear portion is a bit odd, when looking at the design view. I only want a 1.5" can, but I need to cover the gas block.
I'm planning a rear piece to align off the bbl, seal the tubing and cover the block.
The tube's OD will decrease, moving forward.

Not 100% sure about the bbl's vented ports, but, either way, the initial gases will be vented rearward.

[0101silent]

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[RJT]

And the slits in the barrel are EDMed to vent gas into coaxial chambers and sequester off boreline until the later chambers begin to normalize.

If you don't mind where do you send the barrel out to get EDM'd and what does it cost?

http://www.magnaport.com/index.html

[whiterussian1974]

Really? No comments about design features, expected results, or advantageous changes?

Please fellas. I'm looking for input and criticisms that will spare me wasting a F1 stamp and the cost of EDMing the barrel.
So any extra input from you geniuses w experience would sure be welcome.

[T-Rex]

I take it this is for .308/7.62?
What length barrel?
Auto, semi or bolt?
Supers, subs or both?

All in the details

[Dr.K]

I take it this is for .308/7.62?
What length barrel?
Auto, semi or bolt?
Supers, subs or both?

All in the details

I second these questions.

[whiterussian1974]

I take it this is for .308/7.62?
What length barrel?
Auto, semi or bolt?
Supers, subs or both?

All in the details

It was intended to be scalable. .308, .338, 375.
Yes, the 1st apps would be for .308, 30-06, .300WSM.
All Supers. 20-22" bbl. Semi, but also some bolt usage. Only slow fire. 1 of the elements would be for lowering ejection port noise. Since Supers would generate high LOS sound transmission and provide line source signal, I'm only trying to lower point source signal for the area near the shooter so as not to deafen those nearby or unduly scare any predators such as coyotes nearby in case I'm pelt harvesting.
I've probably over-designed w barrel ports and reflex chamber. Just trying to wring out every known element that I;ve seen work to get blast as low as possible. That way the crack would be the only sound, not the blast that's associated w firearms.

[T-Rex]

IMHO the slits are going to hurt you. They start about 4" back so once the pressure bleeds off, your 20" bbl is now acting like a 16" (pressure wise).
I'd think something along the lines of 2 rows of (4)- 1/8" holes, 90* arrayed around the bore, just behind the muzzle threads.
Then have a flat washer, around the muzzle device, between these holes and the muzzle device's holes. Something like you have w/o the washer near the bbl cuts.
You'll have a chamber for the initial release, a chamber for the muzzle device venting and the traditional blast chamber.
With all of this volume, I'm not sure if you'd need the end cap vent holes, but Gunny might be able to weigh-in a bit on that.

[Hard_ware]

IMHO the slits are going to hurt you. They start about 4" back so once the pressure bleeds off, your 20" bbl is now acting like a 16" (pressure wise).
You'll have a chamber for the initial release, a chamber for the muzzle device venting and the traditional blast chamber.
With all of this volume, I'm not sure if you'd need the end cap vent holes, but Gunny might be able to weigh-in a bit on that.

+1
Additional outer sleeve of lower density material will help with resonance and tone, but adds some weight.
Use all of the barrel to push the pill for supersonic.
If only shooting subs drill away in the barrel as far back as you want provided the pill is moving 1050fps upon exiting the barrel and make integral suppressor. Reflex chamber will help with unburnt powder flash. Type of powder you use if you load your own ammo effects this as well. Sound AND fire ball at night will give your location away, sonic crack will not as this eminates from the supersonic pill.
Exit supersonic shock wave cannot be eliminated passively as the pill will be traveling above speed of sound thus the wave will be generated by the speed.
The hole in the end lets the noise out
Nice design!
Just logged in, so sorry for late response

[whiterussian1974]

My thought was that even w venting, there would still be substantial pressure for the last 4"s. However, venting prior to exit would force premature "uncorking" and lower precursor wave + initial blast. The slits would also function more efficiently since the bullet would help force the gas sideways by limiting its forward access. A muzzlebrake would allow too much gas to exit via boreline, only diverting the % that contacts the brake. (ie: sidelobes, rather than main jet.)

But thanks for any and all comments/suggestions no matter when you post. I'll be alerted to thread additions next time I login. And there's no rush to make. I'd rather the design be best than first.
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I agree about super flight noise. However this is semi-directional and can be dealt w through environmental methods. I'm working on point suppression so that any game won't be able to tell where the shot came from. They'll just hear a snap and see their packmate fall. ie: coyotes.

[gunny50]

My thought was that even w venting, there would still be substantial pressure for the last 4"s. However, venting prior to exit would force premature "uncorking" and lower precursor wave + initial blast. The slits would also function more efficiently since the bullet would help force the gas sideways by limiting its forward access. A muzzlebrake would allow too much gas to exit via boreline, only diverting the % that contacts the brake. (ie: sidelobes, rather than main jet.)

But thanks for any and all comments/suggestions no matter when you post. I'll be alerted to thread additions next time I login. And there's no rush to make. I'd rather the design be best than first.
---
I agree about super flight noise. However this is semi-directional and can be dealt w through environmental methods. I'm working on point suppression so that any game won't be able to tell where the shot came from. They'll just hear a snap and see their packmate fall. ie: coyotes.

WR
I do think that in your design the porting can help, it is not necessarily needed but think about those bore evacuator (see it as a pressure equalizer) on battle tanks they have ports on the barrel and that still works fine. (good read -> http://www.ciar.org/ttk/mbt/papers/symp_19/LD08_273.pdf - http://www.ciar.org/ttk/mbt/papers/symp_19/LD09_281.pdf - Engineering Design Handbook; Guns Series, Muzzle Devices", AD838748, US Army
)
So why not use it to fill your volume to the max. and EDM ports would be a great help to do that.

Maybe even close the chamber around the vents so that they do react like the smoke evacuators and release the pressure after projectile leaves the bore. (controlled pressure release.


Ported endcap will lower the uncorking tone.

Gunny

[Capt. Link.]

Just my opinion but if this is a detachable suppressor for supersonic ammo the use of ports is not required or recommended.A muzzle brake will dump all the gas necessary and the suppressor need not be large or fancy.A coaxial design using the brake as a mount will allow the rifle to be useful with or without the suppressor attached.
-CL

[whiterussian1974]

Thanks for PDF links Gunny. I'll have to do off-line reading later.

Capt: thanks for your input, too. I guess that I'll just have to try it and then report back.
Or maybe a NZ would be able to test the theory. If they already have a ported barrel, the only added cost would be the freeze plugs b/t the ports and muzzlebrake.