Secondary Blast Baffle discussion

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Secondary Blast Baffle discussion

Post by John A. » Sat Jun 17, 2017 11:45 am

I'm a long time member here though I don't post many topics, but this is a subject that I don't think has ever came up.

A member recently posted the question, is an expansion chamber needed or important or something along those lines.

And instead of hijacking that topic, I wanted to post a few things that I have found over the years, and hopefully to garner some discussion about it from other enthusiasts and especially if any manufacturers have experimented around with this.

I will be the first to say that there will be a blast baffle, or expansion baffle somewhere in the silencer, but it will be largely up to the maker where that will be. That much is unavoidable.

But I have found that placing a baffle really close to the muzzle does in fact help reduce the sound. Whether it's first round pop, or all the shots. I used to attribute FRP to reducing the amount of space/air for the gas to ignite, which I think is correct. But I also believe there is more going on than just that.

I know a lot of people who have said the blast baffle is the most important one of them all. Shouldn't be ported, etc. because it has the most affect on the bullet.

But in years of REALLY looking at and studying how things work, I can't help but to think that there are a few important baffles.

The blast baffle and the next several baffles seem to have the most fouling. Many would say because the pressure drops the farther away from the muzzle. I would tend to agree, but I think there is more going on than that.

Here are a few different photos that I want to look over.

Notice that in virtually all of the destructive tests of silencers you'll see, regardless of caliber, will be the hottest just prior to the center of the can.

* just to give credit, this photo was snipped from tarheelstatefirearms scrolling banner on top of their page for reference

Image

And also, I have watched virtually every slow motion video of gunshots that I can find.

This too kind of points toward the bulk of the gas expansion isn't going to be at the blast chamber, but a few inches out of the bore. Kind of maybe explaining the photo above of all of the destructive tests that I have seen.

**These photos from mythbusters also clearly shows the gas/pressure moving forward and expanding the most several inches away from the muzzle in normal conditions.

Image

As you can see in this screenshot below, looks like the bulk of the gas is likely to pass through the expansion chamber bore almost entirely, only to expand later in the stack.

Image

So, I'm starting the topic for discussion to get some of your thoughts and opinions.
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Re: Secondary Blast Baffle discussion

Post by Sergeant » Sat Jun 17, 2017 2:51 pm

Touching the blast chamber/blast baffle. I did a 4 mag dump on a 5.56 can in the name of R&D. It didnt get cherry red forward of the blast baffle. The first baffle had some pitting and wear but the 2nd baffle still had sharp edges and clean metal. The 1st baffle was about 0.5 inches off the muzzle brake.
I interpreted that the first baffle took the brunt. But what do you think?

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Re: Secondary Blast Baffle discussion

Post by John A. » Sat Jun 17, 2017 5:27 pm

I'm not saying the blast baffle doesn't take a lot of punishment. We both know that there is a lot of erosion from heat and unburned powder pitting it.

Even with 22 cans, the first several baffles are always the dirtiest and worst.

I'm curious if anyone has ever made a secondary expansion chamber though and how it worked out?

I've never seen a commercial one that way, but from all the research that I've done watching slow motion videos, and how many folks have shown cherry red cans, and how the expansion acts (normally) that it may be something beneficial to try.
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Re: Secondary Blast Baffle discussion

Post by quietoldfart » Sat Jun 17, 2017 6:20 pm

In my most recently completed takedown .22lr rifle I used ten K baffles, ranging from about 0.55" long to 0.80", all 0.865" OD. The first K is 0.30" from the muzzle. After the first five baffles I put in a spacer tube 0.7" long, after having tried an eleventh K baffle in that position. 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 thst way. My baffles get slightly longer as they progress down the stack towards the end cap, somewhat randomly, but a gradual progression towards greater length, primarily in the face skirts but also a bit more in a flat tubular section after the cones.

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Re: Secondary Blast Baffle discussion

Post by John A. » Sat Jun 17, 2017 9:43 pm

2db is a substantial difference, especially since you omitted a baffle. That's contradictory to what I would have thought.

From my rough guesstimate, the long spacer you put in is about 3.5 inches from the muzzle, and about where the widest part of the smoke/expansion occurs from judging by the still photos above so I'm wondering if there isn't a "sweet spot".

In the same circumstance, in my first suppressor (9mm), I also put a longer spacer near that point, and it is noticeably more quiet than my later 9mm build. I don't have a meter, but I can tell by ear and my eyes closed which was my oldest just by sound (because it sounds so much better).

Granted the newer can is not as large of a diameter and a little shorter, it's daylight and dark different sounding.

Also, in my newer 9mm can, I experimented with arranging and re-arranging the longer and shorter spacers in different places.

Mine was also noticeably more quiet with a really short expansion chamber and getting progressively longer toward the end as well.

And this is why I wanted to start the topic. To find out what other people have tried and why and how it worked out.

I don't pretend to understand all the little specifics of everything, but I do enjoy learning and sharing and I appreciate you taking the time to tell what you've found. I can say that my limited experience is very similar.
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Re: Secondary Blast Baffle discussion

Post by fishman » Sat Jun 17, 2017 10:01 pm

the reason the torture tested cans don't get as hot near the blast chamber is because the barrel acts as a heat sink drawing heat out of the endcap.
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Re: Secondary Blast Baffle discussion

Post by John A. » Sat Jun 17, 2017 10:37 pm

There is some heat conduction that goes on. No dispute there. And not a lot different than how a kitchen stove heats up your skillet.

But I think there's more going on there than just that.

If it was simply metal to metal contact, the baffles and the tube would heatsink itself wouldn't it? And where is the tube the hottest?

About mid-way up the tube.

A lot of older guns actually had barrels made like a heat sink to help with cooling. The Thompson machinegun barrel being one that comes to mind first. Even a lot of guns today have fluted barrels. The more surface area, the better.

I know that it's a different subject, but I always thought it would be a good idea to do outer tubes like that.

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Re: Secondary Blast Baffle discussion

Post by jnjproto » Sun Jun 18, 2017 1:28 am

I'll throw a few more questions out. I made my blast chamber walls .050" thick with 17-4. My spacers and cones are one piece with spacer walls at .020" thick. Couple this with .065" wall ti tubing. Could this be why the blast chambers don't show the heat as much as later in the stack? I think the reason you see the gas cloud a short distance from the muzzle is twofold first when immediately ahead of the muzzle it is at a velocity several times the speed of the bullet and has not been diluted in the atmosphere. Second is that a short distance from the bore it has slowed considerably and is free to travel in any direction. How this works inside a confined space is open to conjecture among us amatuers. Maybe considering the increased expansion downstream some sort of coaxial design where the outer chamber is only accessible from the midpoint would be beneficial. I also wonder about decreasing bore size as you get closer to the muzzle.
I am starting on my second form one. I am basically scaling down my first can except I will have varying skirt lengths so I can increase or decrease the baffle spacing towards the muzzle. I hadn't considered totally random spacing, but will try that too.
An interesting discussion, I look forward to it.

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Re: Secondary Blast Baffle discussion

Post by Sergeant » Sun Jun 18, 2017 9:17 am

So you're thinking a small first blast chamber, blast baffle, then a small second chamber. Is that right?

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Re: Secondary Blast Baffle discussion

Post by John A. » Sun Jun 18, 2017 10:28 am

jnjproto wrote:first when immediately ahead of the muzzle it is at a velocity several times the speed of the bullet and has not been diluted in the atmosphere. Second is that a short distance from the bore it has slowed considerably and is free to travel in any direction. How this works inside a confined space is open to conjecture
I tend to agree.

As an example, when gas pressure has momentum (even a short stream of steam from a pressure cooker), will exit the pressure cooker vent in a cone shape that takes a while before reaching its' largest diameter, which is why I don't think the barrel acting as a heat sink is all that's going on.

And also why I don't think the blast baffle is the largest determining factor of how a can is going to work either.

I have even taken spoons and forks and things and placed in the steam just to see how things react. If the HPA gets passed, I may even make a tube from clear plastic so that I can attach it to a device so I can watch how different baffles and spacer lengths affect things. But I'm afraid to do that with todays current laws.

I feel better when I can actually see how real world things react. Steam is just one of the things I study these days now that I quit smoking about 7 years ago.

But I do enjoy watching how things work. Escaping pressurized steam is not inherently different than what takes place when a gun is fired. At least in a lab type setting.

I am just one of those guys that truly wants to grasp what's really going on, rather than just copy a design that everyone else is using and spout of what they heard on the internet.
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Re: Secondary Blast Baffle discussion

Post by fishman » Sun Jun 18, 2017 11:53 am

A jet of steam isn't a great comparison because in a silencer, the gas can't just shoot straight out in a cone, the bullet is in the way. This, in my opinion, is what diverts so much of the blast into the first chamber instead of letting it shoot straight down the bore.

The speed of the bullet is an important factor here. A 223 bullet is going to get out of the way much faster than a subsonic bullet will.
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Re: Secondary Blast Baffle discussion

Post by John A. » Sun Jun 18, 2017 4:50 pm

The thing about that though, the speed of the gas pushing the AR bullet is still traveling as fast as the AR bullet.

The speed of gas pushing the 9mm bullet, is still traveling as fast pushing the 9mm bullet.
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Re: Secondary Blast Baffle discussion

Post by fishman » Sun Jun 18, 2017 7:43 pm

The gas wants to go much faster than a 9mm bullet. That's why it gets pushed off the bore line when it hits the back of the bullet.

This might still be happening after the bullet has passed through the blast baffle. Not so much with a 223 bullet.
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Re: Secondary Blast Baffle discussion

Post by garredondojr » Sun Jun 18, 2017 10:33 pm

man why did I click on this thread. :? I just got my first form 1 back yesterday(344 days!) and actually taking a break on it right now.

so let me try and understand your theory here. your thinking of making the blast chamber as small as possible the adding a secondary blast chamber after the first thinking the gasses are jetting past the first baffle? the idea seems sound if it is a direct thread but wouldn't running a brake, comp, or flash hider kind of disrupt things?

I don't need any help trying to change my mind on design again. :mrgreen: :mrgreen:

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Re: Secondary Blast Baffle discussion

Post by John A. » Sun Jun 18, 2017 11:29 pm

garredondojr wrote:man why did I click on this thread. :? I just got my first form 1 back yesterday(344 days!) and actually taking a break on it right now.

so let me try and understand your theory here. your thinking of making the blast chamber as small as possible the adding a secondary blast chamber after the first thinking the gasses are jetting past the first baffle? the idea seems sound if it is a direct thread but wouldn't running a brake, comp, or flash hider kind of disrupt things?

I don't need any help trying to change my mind on design again. :mrgreen: :mrgreen:
Yes.

And an internal/directional muzzle brake will change things quite a bit too. Which is good for suppressors. I plan to use one inside of my latest F1, if atf ever decides to sign and return it. :roll: That one will be for a blkout with an integral portion with a reflex chamber over the barrel.

A baffle is likely to change how some of the gasses work too.

Things are going to be pressurized inside of a can regardless, but from just rearranging short spacers and long spacers, if all else is equal, I can tell a difference in how it sounds. And it looks like I'm not the only person who's experimented around and came to the same conclusion that I have.

I also encourage discussing high and low pressures within a can too. There are a few ported designs (like the omega baffle for instance) that creates a tube within a tube. Really, just about any kind of porting or clipping introduces high and low pressure areas.

K baffles do too.

Which is why I think that it often helps in sound suppression.

Like I mentioned, I have tried to apply how the real world works with regards to how I design my cans. I designed and built my first one more than a decade ago and I have literally studied everything I can put my hands on about how pressures and flows work.

That's even a big reason why I got into reloading. Applying a lot of what I have learned about burn rates and stuff trying to choose the best powders to get the best suppression.

But I'm getting too far off subject.
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Re: Secondary Blast Baffle discussion

Post by garredondojr » Mon Jun 19, 2017 1:39 am

Sounds like you and I are one in the same, however you have a decade plus headstart on me. I couldn't tell you how many hours i've wasted on quickload and load development myself. :oops:

I feel your pain with the ATF I still have a paper form 1 from 7/12 that i'm waiting on. willing to bet it takes a whole year!

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Re: Secondary Blast Baffle discussion

Post by jnjproto » Mon Jun 19, 2017 2:45 am

I think it was Speer's 13th edition loading manual that had a very nice picture of gasses surrounding a bullet a short distance from the muzzle. This picture along with others I have seen influenced the way I made pistol compensators over twenty years ago. The base of the bullet does impead the flow of gasses, but only slightly. I have read that gasses are traveling at 3 to 4 times the speed of the bullet. Once the gasses are unrestrained by the barrel they are free to travel in any direction. Here is where Newton's laws come into play. An object in motion will remain in motion until acted upon by an outside force. The bullet and air are those outside forces. Just as we change lanes to pass a slow car then return to our original lane so too the propellant gasses. And some cars turn in directions no longer consistant with the slow cars, just like the gasses. Now back to the compensators. I surmised the most effective way to make use of the gasses in low pressure cartridges was for the front shoulder of the bullet to reach the baffle, and seal the port so to speak, at the same time the base cleared the last baffle. While I did not have access to test equipment to validate my theory I received enough positive feedback to contine to design compensators around the bullet being used. Now for the ah-ha moment, would this benefit a suppressor? I am going to explore this in cad and see what I come up with.

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Re: Secondary Blast Baffle discussion

Post by doubloon » Mon Jun 19, 2017 8:08 am

jnjproto wrote:... I have read that gasses are traveling at 3 to 4 times the speed of the bullet. Once the gasses are unrestrained by the barrel they are free to travel in any direction. ...

https://www.youtube.com/watch?v=7y9apnbI6GA&t=10
http://www.youtube.com/watch?v=BDtd2jNIwAU MUSAFAR!
http://www.youtube.com/watch?v=8CrOL-ydFMI This is Water DavidW
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Re: Secondary Blast Baffle discussion

Post by Paco664 » Mon Jun 19, 2017 11:47 am

doubloon wrote:
jnjproto wrote:... I have read that gasses are traveling at 3 to 4 times the speed of the bullet. Once the gasses are unrestrained by the barrel they are free to travel in any direction. ...

https://www.youtube.com/watch?v=7y9apnbI6GA&t=10
this video along with the photo of the torture tests with the suppressors glowing in the middle confirm OP's hypothesis...

watch the blast and see approx 3"~4" from the muzzle the gases swirl out and make a curlyq...

wouldn't this argue for the 2nd larger expansion chamber farther into the suppressor tube?

OMG please congress hurry and pass the HPA so these questions can be answered...

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Re: Secondary Blast Baffle discussion

Post by cdhknives » Mon Jun 19, 2017 2:00 pm

Your premise that the gases in the gas column are travelling only as fast as the bullet is (mostly, really only at the base of the bullet and slower behind down to zero at the primer due to the way gas expansion works) correct 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. There are formulas for pressure vs. sonic velocity that might give clues as to how fast they really are, but I am long past those college classes. Anyway, pay very careful attention in those super slow motion vids of bullets exiting the bore. The large plume starts mushrooming out at the muzzle but very quickly moves down range...even gases have inertia. My brain just imagines the jet of gases erupting from the muzzle about the same time the bullet mostly plugs the bore in the blast baffle to be ideal for maximum capture. Is the second baffle going to be almost as important? Maybe. It sounds like a good starting point to me in determining the spacing of the first couple of baffles, but lots of threads here dispute this conclusion. The cooling effect is also important to suppression, and seems less concerned with spacing than qty of metal for a heat sink and surface area for heat transfer.

Bottom line, I think imagination will only get us so far, and then either advanced modeling with verification via actual experimentation, or a LOT of experimentation will be required. I find myself getting sooooo lost in imagining things that probably don't matter... :shock:

This kind of 'fun' can drive a curious engineer like myself nuts... :lol:
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Re: Secondary Blast Baffle discussion

Post by John A. » Mon Jun 19, 2017 3:42 pm

I am certainly no engineer. Had several semesters of hydraulics and pnuematics classes in my college days, which I think may have helped understand some about how pressures work in certain conditions.

But I have tried to understand how things work in my quest to do the best I can in what I do. And I have tried to apply what I see in how I make my stuff. And guns and design has been my biggest hobby for the biggest part of my adult life.

Sometimes it works out to the good, and sometimes I have to just sit back and shake my head. :lol:

But this has been something that's been on my mind for a while. And why I wanted to bring it up and at least get the conversation started.
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Re: Secondary Blast Baffle discussion

Post by Paco664 » Mon Jun 19, 2017 5:20 pm

it's a great discussion...

i repeat my hopes and desire for the HPA to pass and we are free to experiment to our hearts content.... i only wish as i finish replacing the batteries in my hearing aids that they would have allowed us of suppressors 30+ years ago when i was a stupid kid....

not now at 48yrs old and 70% deafness in my right ear...

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Re: Secondary Blast Baffle discussion

Post by Sergeant » Mon Jun 19, 2017 6:36 pm

So....with all this in mind, if we were going to test this, say we were a 07/SOT...what would this can look like?

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Re: Secondary Blast Baffle discussion

Post by cdhknives » Mon Jun 19, 2017 6:58 pm

Using this clip for reference:
https://www.youtube.com/watch?v=414hyoK6iW4

Around the 47 second mark it shows that initial blast as the bullet exits very well. The exiting gases are still impinging the back of the bullet and being deflected sideways from the bore axis. Watch how much of the gas cloud is already present by the time the bullet is 2-3 bullet lengths from the muzzle. Notice also the glowing gases are already cooling (no longer glowing) a bare inch or two in front of the muzzle. once the bullet is far enough downrange to see the gas cone exiting the vast majority of the gases are already out...and cooling fast due to the mixing with air and the nature of gas expansion (that old PV=nRT ideal gas formula, yes I know it is an approximation) and dropping pressure.

Based strictly on the progression of the gas cloud, I don't see a secondary blast. It is all a progression to my eye...but I am dang sure no expert, and I made a C in fluid dynamics in college. :lol:
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Re: Secondary Blast Baffle discussion

Post by John A. » Mon Jun 19, 2017 7:15 pm

cdhknives wrote:Using this clip for reference:
https://www.youtube.com/watch?v=414hyoK6iW4

Around the 47 second mark it shows that initial blast as the bullet exits very well. The exiting gases are still impinging the back of the bullet and being deflected sideways from the bore axis. Watch how much of the gas cloud is already present by the time the bullet is 2-3 bullet lengths from the muzzle. Notice also the glowing gases are already cooling (no longer glowing) a bare inch or two in front of the muzzle. once the bullet is far enough downrange to see the gas cone exiting the vast majority of the gases are already out...and cooling fast due to the mixing with air and the nature of gas expansion (that old PV=nRT ideal gas formula, yes I know it is an approximation) and dropping pressure.

Based strictly on the progression of the gas cloud, I don't see a secondary blast. It is all a progression to my eye...but I am dang sure no expert, and I made a C in fluid dynamics in college. :lol:
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.
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