Secondary Blast Baffle discussion

[doubloon]

... right up to the point the bullet uncorks the barrel. At that point the internal pressure allows them to jet out at many times the speed of the bullet. ...

[cdhknives]

I know that I said a secondary blast chamber in the title, but I meant secondary expansion chamber, which I did specify in the first post. Based on the point where the bulk of the gasses are expanding and swirling.

About 3.5" outside of the muzzle.

Sorry.

I'm with you now. That is kind of the point where I would say the gases have mostly expanded to full volume. The point of a suppressor is kind of to contain all that swirling inside the can to allow it to cool and break up the shock wave from supersonic gases jetting out as the bullet leaves the barrel.

Since rearranging the baffles should not count as modification in my limited understanding of form 1 legalities, simply make one baffle a spacer and rearrange it in your baffle stack to see what effect it has. I would expect more baffles to be quieter than a secondary expansion, but at least one person above seems to have empirical evidence to the contrary.

That's part of our fun...experimentation. Too bad it is so dang expensive for us hobbyists.

[fishman]

Aren't ALL the chambers between baffles really expansion chambers? The purpose of the blast chamber being particularly large is to quickly drop the gas pressure before is starts imparting force on the blast baffle so that it doesn't blow the endcaps off and baffle stack out the front of the can. Cartridges with low muzzle pressure don't need ANY significant blast/expansion chamber.
Having a second large expansion chamber will offer no benefit IMO. I bet it will do more harm than good. Maybe it has merit as a means of preventing gas blowback.

Threes a reason the top industry cans don't have them.
Still, a can with several 1/8" spacers that could allow the baffle spacing to be rearranged would be cool for testing this.

[yondering]

Still, a can with several 1/8" spacers that could allow the baffle spacing to be rearranged would be cool for testing this.

That's how I built my first F1 can (except with 1/4" and 1/2" spacers), for exactly that reason. All the same parts went in the suppressor each time, but they could be re-arranged. I tested different configurations mostly with subsonic 300 Blk and subsonic 35 Remington, here's what I and my witnesses observed:

- Large expansion chamber and tight baffle spacing afterwards: increased first round pop but quietest subsequent shots
- Small expansion chamber and even baffle spacing: little or no FRP, louder subsequent shots and sharper tone
- Moderate expansion chamber and progressive baffle spacing (tighter spacing towards suppressor exit): very slight FRP, good tone, best balance of FRP and subsequent shots overall.

I left the can in the third configuration. This was with simple cone baffles, all clipped except the blast baffle. Results might be very different with other baffle styles or other calibers. This can does work very well on subsonic and supersonic rounds though and ended up only slightly louder than my Mystic X but with better accuracy in many rifle loads.

... right up to the point the bullet uncorks the barrel. At that point the internal pressure allows them to jet out at many times the speed of the bullet. ...

What is that picture supposed to prove? That the bullet eventually outruns the gasses? Duh, that's why we shoot things with bullets, instead of just hot gas. If you looked the time before the image you posted, you saw the gas does move faster than the bullet until pressure is relieved, and cdhknives is completely correct.

[yondering]

I am certainly no engineer.

I am. I appreciate your observations and thought provoking comments.

The one big thing I see missing from the discussion though is this:

The sound we're trying to suppress is a pressure wave, not hot gas. They are related, but not the same, and need to be thought about differently. That's different than designing a muzzle brake, where the goal is to redirect the gas. Our goal with a sound suppressor is to dampen and disperse that high pressure sound wave, which is caused by the sudden uncorking of the muzzle pressure, which in turn is caused by the generation of that hot gas through combustion. The gas alone is not the focus.

[doubloon]

...
What is that picture supposed to prove? That the bullet eventually outruns the gasses? Duh, that's why we shoot things with bullets, instead of just hot gas. If you looked the time before the image you posted, you saw the gas does move faster than the bullet until pressure is relieved, and cdhknives is completely correct.

I did look before that time and at some the gas was maybe an inch in front of the bullet for a few microseconds. I made no claims about gas never being in front of the bullet, try not to be so sensitive.

[T-Rex]

I didn't read all the replies, so for that I apologize, but have we included/mentioned the use of baffle porting?
Equalizing all spaces into, essentially, one chamber is another way to look at it.
The coaxial design can be another way to express an additional expansion chamber. After all, there can be only one blast chamber

[cdhknives]

Jets of gases are limited to sonic velocity by the nature of shock waves in gases. As the gas compressed, the speed of sound increases, so the speeds are not strictly limited to MACH 1@sealevel (sonic velocity relates strongly to density and density increases as pressure increases). I have studied this a fair bit in the context of high velocity gases in pipes and measurement of same (I am an EE doing Instrumentation and Controls for petrochemical facilities in my primary job).

Around 1125 fps is sonic velocity at standard T and P and Rh. Compress air (including the temporary cone of high pressure as a bullet exits the barrel) and the sonic velocity goes up as the gas density increases. Long story short, that shock wave of the gases exiting and trying to go above sonic velocity is the majority of the gunshot report you hear. This is pretty well understood by most here I assume.

The vid clip shows this well. Note how in the first inch or so of bullet travel you get 2-3x travel from the gases...plainly illustrating the fact that they are traveling much faster than the bullet for the first couple of inches. They rapidly slow down due to shock effects (cone and deflection from the bullet base) and then transition to friction with surrounding air. By the time the bullet is 8-10" in front of the barrel the gas plume appears to be near equilibrium with surrounding air pressure, quits expanding, and just rolls forward slowing and dispersing via friction. Look at the same type vid but from a 300 Mag and that plume is dramatically larger in all respects. The jetting as the barrel uncorks is MUCH more dramatic...the pressure at the muzzle from this (looks like a 45ACP) pistol is very low so the initial supersonic jet is relatively small...hence how much easier a 45 is to suppress as well. Less gas to work.

The first part, the high pressure jet section of escaping gases, is the big noise maker we are trying to contain/modify. Stop/minimize it from generating a shock wave and you kill most of the noise from a gunshot. Once the bullet is at average suppressor length in front of the barrel it is about all over anyway...except for the bullet generated noise and our suppressor doesn't affect that significantly. So basically what happens in that first 2-3 inches of bullet travel is CRITICAL to our suppression. Once the initial shock wave is developed, the noise is too. We gotta kill that in initial shock wave in the first inch or 3 of bullet travel. That is the whole job of our suppressor.

This is my understanding. Feel free to disagree, it is certainly more art than science at some levels...but this is why the form 1 cans I am building will have more baffles than expansion chambers. I just can't wrap my brain around the benefit from a secondary expansion having significant benefit...or better yet as described above the baffle stack is your secondary expansion chamber.

[doubloon]

...
This is my understanding. Feel free to disagree, it is certainly more art than science at some levels...but this is why the form 1 cans I am building will have more baffles than expansion chambers. I just can't wrap my brain around the benefit from a secondary expansion having significant benefit...or better yet as described above the baffle stack is your secondary expansion chamber.

Nice post.

This last part is why I added the xray suppressor vid. I do not claim to have any real understanding or applicable knowledge but observing the xray vid seems to show how the gases are tamed by the full baffle stack and the first 6-7 baffles deal with the bulk of the expansion.

[John A.]

Thanks for posting that doubloon.

I had forgotten watching that video when they first put it on youtube.

[jnjproto]

The more I reflect on this here are my thoughts. The blast chamber has an inverse relationship between FRP and back pressure (applicable only to semi-autos). Volume helps, but at what point do you see diminishing returns? Baffle spacing, that seems to be the real conundrum. Wider spacing, in the middle, has payed dividends in the above mentioned example. I have seen successful commercial rifle designs that only had 3 or 4 baffles and large spacings. I have also heard the Sig suppressor with many baffles get very good reviews. I think with higher pressure the design is somewhat less critical. With handguns and other low pressure rounds the efficiency of the design becomes much more importantly.
I just started working on my second form 1. It is primarily for 22 lr but will see some use on a K-Hornet and .223 with cast bullet loads. I am going to tighten up my baffle stack so that as the bullet enters one baffle it is clearing the one behind it. The theory is like my compensators, the bullet seals off each chamber allowing as much time as possible for the gas to fill the chamber without being able to get around it. At least it sounds good to me. I'll let you know in a couple weeks or so.

[John A.]

I'm looking very forward to hearing how it sounds.

I personally try to cram as many baffles in there as I can for pistol calibers and after this topic though I never considered making them that close, but it makes sense to do that and now I know more of the "why" behind it. Which is why this place rocks.

But it doesn't hurt to make a long chamber to move around and rearrange either

[T-Rex]

Since gases expand uniformly, the following must be equal
a. bullet length (from ogive to base)
b. baffle to baffle distance
c. baffle bore OD to inner tube wall distance

At the least, a & b would need to be greater than c, if you wanted to rely on the chamber filling before the projectile "uncorks" the previous baffle. With something as small as a 22lr, I think your baffles would be so close, they'd almost be stacked on top of each other.

[doubloon]

Since gases expand uniformly, ...

I thought there was a difference between free expansion and isothermal expansion.

Heated gases will expand faster closer to the heat source?

[jnjproto]

I am making my baffles .312 apart, which means there will be about 12-14 in the suppressor. I measured the length of the body diameter on the bullets I plan to shoot. The .22 LR's run around .28" to .29". My cast bullets run from .3" to .375". And 55 grain fmj run about .4". The design follows my first one with 60 degree 17-4 cones with integral spacers 1 inch diameter and 1-1/8" diameter ti tubing. It will be about 8.5 inches long. The blast chamber is 1 inch to the foward edge. My blast baffle is kind of unique in that it has an integral tube extending rearward to about .3" from the muzzle. I've not seen one like this that I can recall. My theory is that the gasses will take longer to get back to the bore with this extension tube. Will it make a difference, who knows, but we shall see.
With regard to the original comment about the middle of the cans getting the hottest. Could it be because the gasses have mixed with oxygen to the point that it ignites at that time? Well here's to the neverending quest.

[Capt. Link.]

Many interesting points but not quite sure what the question is.

Secondary expansion chambers are proven to be effective. #7 is a older successful full auto design called the Triple X Warrior. Its main claim to fame is it did not melt during automatic fire.Please study #4's huge initial expansion chamber. Most of the other suppressors use a ported blast baffle plus a muzzle device for early gas disruption these daze.


I would say that first baffle placement is NOT the most important aspect of suppression or FRP reduction gas flow and retention is.Many oversized suppressors are not effective because of lack of circulation of gases.

quietoldfart: I was curious regarding something about this which Capt. Link had told me in a PM about his own experimentation in breaking up wave patterns mid-stack. The result was a quieter rifle. By about 2dB according to my cheap SPL meter. I've kept it this way. My baffles get slightly longer as they progress down the stack towards the end cap

A suppressor is also a acoustic filter. Changing the inter baffle spacing gas flow or the baffle type will alter what you hear.Again secondary gas expansion chambers can be used.A technique I call progressive spacing in which baffle interval and porting become larger as the pressure decreases.I find this and the use of secondary expansion chambers or selected porting have a softer sound.I have no SPL data to prove if its quieter but the tone is different.

Many of today's design uses porting instead of the "secondary chambers also known as equalization chambers" we used years ago.
Here is the Sig suppressor that features porting gas disruption and a secondary expansion chamber in the end cap.


Large expansive spaces will reduce noise through expansion and cooling but not as effective per cubic inch of internal volume as directly exposing the gases to baffling causing gas flow and turbulence.

I love the X-Ray of the sparrow,it shows why they updated the core.Putting out the flame early allows more of the internal volume to be used for gas pressure reduction.



-CL

[3strucking]

Are all of the cones ported on the sig?

[doubloon]

Many interesting points ...

-CL

Somehow I knew these pictures would surface.

Good job on the accompanying narrative.

[T-Rex]

Are all of the cones ported on the sig?

All evidence I've seen would have me believe so.

[fishman]

Are all of the cones ported on the sig?

All evidence I've seen would have me believe so.

I don't believe they're all ported the same though. Ive seen pictures that made it look like the quantity and location of the ports varied.

[T-Rex]

The blast baffle appears thicker and its holes slightly larger.
I've seen pics where all the ports were, pretty much, lined up and others where they were not.
I think all baffles are ported, but that they just drop the stack together, at random.

[Capt. Link.]

To the best of my knowledge the stack is fully ported and aligned.
-CL

[T-Rex]

Check these 2 pics out. Slightly different, but lending the same idea. Looks like someone did their best to align the ports.



Then, there is this pic. You can clearly see that the blast baffle and last baffle ports are about 45* out.


Just adds more question for the need of alignment. Obviously, the equalization would happen much faster when aligned. I wonder the tone difference between aligning the ports and having them 45*, successively?

[fishman]

Clips are aligned and uniform. Ports are not.

[Paco664]

once again i repeat i cannot wait for the HPA to pass... THEN there will be a LOT of experimenting...

this is a fascinating subject...