Fourteen (14) LDC Test

[WhatUPSbox?]

It seems safe to say that most any moderator with properly built internals (meaning not just an empty can) ...

That may actually be an interesting data point. Taking one of the larger LDC's that you can disassemble and comparing it as built and with the internals removed.

Stan, actually I may have already had some experience in that arena. Long ago (mid-90's) someone among our local Hawaii airgunning group at the time decided to make empty "cans" for us to try out.

They were nicely machined and everything, and if we had 3D printing back then or even any basic knowledge of exactly "how" a silencer looked on the inside, we may have made more progress but as it turned out, the cans were not much quieter (you could tell the volume was a bit less, but it was still irritatingly loud and metallic sounding as we shot it through a PCP) and the main point was ... the pellets seemed to go all over.

The non-uniform turbulence going on inside the empty can was enough to throw the pellet path off, and not necessarily in a consistent manner (it's not like the POI just shifted, the pellets were landing all over the place).

Charlie, that's interesting. I wonder how much of the accuracy effects is due to the region just outside the crown (adapter ID?) and how much is turbulence in the can.

[mrbulk]

Just wanted to add a minor comment.

While doing this test and feverishly spinning units on and off in a hurry, I realized I had to go slow and careful when putting on the units with threaded plastic end caps. Inattentive cross threading is a very real consideration with these type units and I thought I would mention it.

The makers of some units, like the Rocker1 for example, wisely provide a metal threaded rear cap despite the rest of the body being made of non-metal material. This makes it easier to install, especially considering real world use like in less than ideal light, with gloves on, etc.

[mrbulk]

Stan, I’m unsure if the area immediately past the crown affects pellet travel that much as long as the original machining and construction in that area is concentric to the barrel bore. However, once the pellet enters the wild west turbulence going on inside the much larger interior volume of the LDC itself then I’m thinking all bets are off.

[Rick67]

What are the dimensions on the silver LDC?

I am partial to silver, you know.

Thanks, MB sir 

Thanks Richard, the dimensions are 1-1/8” x 7-3/8” 

Gracias, Senor 

[subscriber]

Folks,

I have attempted to model the unrestrained muzzle plume of an air rifle.  The image below is supposed to indicate the change in plume shape as the projectile moves away from the muzzle.

What is clear, is that the projectile's base acts as a "screen" that directs the plume mostly radially just after "uncorking".  Then, as the projectile travels further away from the muzzle, its "shadow" in the plume becomes less significant.  A few inches away from the muzzle, the plume of air overtakes and surrounds the projectile. 

Yet, the further away from the muzzle, the lower the air pressure acting near the base of the projectile.  I also suggest the air plume velocity at perhaps 4 inches from the muzzle no longer has very much potential buffeting effect on the projectile (depends on the power level, and if there is an upstream air stripper).  We can argue about the exact numbers, but my point is to recognize what the air normally does, before we constrain that air movement inside the cylindrical body of a moderator. 

The three images below depict air flow at the open muzzle of a .22 caliber airgun, shooting a generic slug.  The first image shows the projectile base a distance of 0.1" from the muzzle face.  The second image, 0.5".  The third, 2" away.

The images are my rendition of what happens to the gas flow just after the projectile clears the muzzle; based on contemplating slow motion video of firearms and airguns (when they show a visible water vapor plume).

Now, imagine constraining such an air plume by adding a moderator, having a 1" ID.  If there are no baffles to strip off the air and interrupt the plume propagation, that air would tend to be reflected off the inner tube walls, and back in towards the path of the projectile.   Such air, free to do its own thing in an "open can", would be more likely to buffet the projectile; unless the tube ID was large enough that the reflect air effect, happened substantially after the projectile had passed.

[mrbulk]

Folks,

I have attempted to model the unrestrained muzzle plume of an air rifle.  The image below is supposed to indicate the change in plume shape as the projectile moves away from the muzzle.

What is clear, is that the projectile's base acts as a "screen" that directs the plume mostly radially just after "uncorking".  Then, as the projectile travels further away from the muzzle, its "shadow" in the plume becomes less significant.  A few inches away from the muzzle, the plume of air overtakes and surrounds the projectile. 

Yet, the further away from the muzzle, the lower the air pressure acting near the base of the projectile.  I also suggest the air plume velocity at perhaps 4 inches from the muzzle no longer has very much potential buffeting effect on the projectile (depends on the power level, and if there is an upstream air stripper).  We can argue about the exact numbers, but my point is to recognize what the air normally does, before we constrain that air movement inside the cylindrical body of a moderator. 

The three images below depict air flow at the open muzzle of a .22 caliber airgun, shooting a generic slug.  The first image shows the projectile base a distance of 0.1" from the muzzle face.  The second image, 0.5".  The third, 2" away.

The images are my rendition of what happens to the gas flow just after the projectile clears the muzzle; based on contemplating slow motion video of firearms and airguns (when they show a visible water vapor plume).

Now, imagine constraining such an air plume by adding a moderator, having a 1" ID.  If there are no baffles to strip off the air and interrupt the plume propagation, that air would tend to be reflected off the inner tube walls, and back in towards the path of the projectile.   Such air, free to do its own thing in an "open can", would be more likely to buffet the projectile; unless the tube ID was large enough that the reflect air effect, happened substantially after the projectile had passed.

I see your point and agree. All other things being equal, air will tend to spread uniformly out into open space Unless affected by surrounding structural inconcentricities and/or adjacent obstacles such as tube walls, etc.

[WhatUPSbox?]

You've probably seen this high speed Schlieren imaging of a pellet. I don't know what gun that is, but I'm assuming the barrel is about 1/2" diameter for reference. I think it is best viewed at the .25 speed. To me it looks like the pellet is free of the muzzle blast at about 3" and the turbulence stays relatively contained radially. Of course it will behave somewhat differently inside a 1-1 1/4" tube but I'm not sure anything bouncing off of the tube walls can catch up with the pellet.

[subscriber]

[mrbulk]

Gentlemen, your fine video examples are indeed appreciated and I'm gonna do some accuracy testing on my own using some airgun projectiles actually fired on target to view the results, and then we'll see how she blows...literally.

[subscriber]

Charlie,

Remember that if a given moderator seems to open groups, it may simply need a little adjustment to the airgun tuning to find its sweet spot.    That said, comparing results obtained with your default tune and projectile would be very interesting also.

[mrbulk]

Charlie,

Remember that if a given moderator seems to open groups, it may simply need a little adjustment to the airgun tuning to find its sweet spot.    That said, comparing results obtained with your default tune and projectile would be very interesting also.

Yeah I’m gonna keep it simple and establish a baseline first. With every single moderator I just tested for output. ;

[Rallyshark]

Awesome, awesome job Charlie!!  I know there is a lot of effort and time involved in a test like this, so big props to you!  I have a few thoughts about LDCs and the things contributed to this thread.  I'm by no means an expert, and just consider myself to have a lot of general knowledge on stuff like this.  I understand it in my head, but I'm not the best at describing these things sometimes.  Thank goodness we have much smarter folks on here to help us understand these things, and put the differences in perspective!

1.  Testing different power levels:  While I absolutely understand people wanting to know how all these LDCs would perform at different power levels, I think it becomes a lot less important as the power level decreases.  I mean, let's be honest, it isn't that hard to make a low powered gun quiet.  Most any sub 20 fpe gun can be made pretty darn quiet with any decent moderator(provided the gun is tuned correctly).  I think the mettle of the LDC really starts to show when you get to the 30 fpe range and above.  I'd like to see a test at a higher power level.  I have a feeling we'd start to see much larger differences as the power level goes up, and I bet 50 fpe would separate the okay from the awesome rather quickly.  That being said, I think the 30 fpe test is probably the best middle ground test that could be run  

2.  As has already been stated, different LDCs will affect accuracy in different ways.  Generally speaking, most will handle accuracy just fine.  A POI shift isn't necessarily a bad thing, and is to be expected with almost any LDC you add to a gun.  As long as that POI is consistent, and the grouping is still there, that's all that matters to me.  Obviously, the only way to know for sure would be to test one on your gun.  Everything from air waste in the tune, to harmonics, and even barrel droop will play into it.  Then you have to factor in the path of the airflow itself, which can affect the accuracy, all other variables aside.  I'll be honest, the air turbulence isn't something I really take into consideration when purchasing an LDC.  I'll just call it a calculated risk on my part,lol.  All of the other factors are higher in importance to me when considering which one to buy.  I'm not saying the turbulence can't be a factor at all.  I just feel like it is a factor that can't be predicted when applying it a large range of guns.  It is just one of those things you won't know, until you try it on your gun.  I try not to worry about things I can't know. 

3.  The other factor that will play a big part in the effectiveness of the LDC will be the type of barrel it is fitted on.  Rather, if the gun is shrouded or has a bare barrel.  A functionally(airflow wise) shrouded barrel will handle a lot of the air, so the LDC has less to deal with.  The bare barreled guns, much like the higher power guns will separate the men from the boys in sound department.  Even more so, a bare barreled high powered gun will really test an LDC  

Again, excellent work Charlie!  Also a lot of good info contributed by others too! 

[mrbulk]

Thanks for the detailed comments Donny. I too would like to test on true bare barreled guns, but the only one I have is an Evanix AR6K which makes a consistently moderate noise from where the air escapes between the pellet cylinder facings and the breech when shot, which does seem to affect the sound meter readings when I trialed it briefly before settling on the Avenger.

Oh well...

[Rallyshark]

Thanks for the detailed comments Donny. I too would like to test on true bare barreled guns, but the only one I have is an Evanix AR6K which makes a consistently moderate noise from where the air escapes between the pellet cylinder facings and the breech when shot, which does seem to affect the sound meter readings when I trialed it briefly before settling on the Avenger.

Oh well...

As a beggar, I can't be a chooser   I appreciate all the testing you were able to do!

[PumaCarl]

I love reading about tests like this, they take a lot of work and are very appreciated! I would only add that from what I have read over the years from other testers and manufacturers is that you can't include the dynamics of a firearm suppressor because in those the gases are still expanding on exit, and into the silencer. Where there is flame there is continuing expansion/pressure. In airguns the air is decompressing on exit, indeed on travel through the barrel and push on the pellet, and this air is also colder on depressurization: exactly the opposite of what happens in firearms. A firearm silencer is dealing with this heat, pressure of continuing expansion of unburnt powder and that noise is being created inside the suppressor itself. Two totally different animals. I really like the 3d printing trend because more people are testing more designs in materials that can absorb sound themselves, in strengths that can handle air gun pressures, and not making unnecessarily heavy firearm units designed to take 60,000psi and high heat. Size does matter, and smaller is better. I have found that at the end of the day I prefer my  DFL Tanto over everything else when considering size, weight, cost, availability and the fact that I have four different end caps so I can move it around guns easily. The Sumo is a little quieter but the Tanto doesn't change my poi, so the Tanto wins. Thanks for doing the review!

[mrbulk]

Thanks for the detailed comments Donny. I too would like to test on true bare barreled guns, but the only one I have is an Evanix AR6K which makes a consistently moderate noise from where the air escapes between the pellet cylinder facings and the breech when shot, which does seem to affect the sound meter readings when I trialed it briefly before settling on the Avenger.

Oh well...

As a beggar, I can't be a chooser   I appreciate all the testing you were able to do!

Naw, you could just loan me all your bare barrel guns, Haw!!! 😉

[mrbulk]

I love reading about tests like this, they take a lot of work and are very appreciated! I would only add that from what I have read over the years from other testers and manufacturers is that you can't include the dynamics of a firearm suppressor because in those the gases are still expanding on exit, and into the silencer. Where there is flame there is continuing expansion/pressure. In airguns the air is decompressing on exit, indeed on travel through the barrel and push on the pellet, and this air is also colder on depressurization: exactly the opposite of what happens in firearms. A firearm silencer is dealing with this heat, pressure of continuing expansion of unburnt powder and that noise is being created inside the suppressor itself. Two totally different animals. I really like the 3d printing trend because more people are testing more designs in materials that can absorb sound themselves, in strengths that can handle air gun pressures, and not making unnecessarily heavy firearm units designed to take 60,000psi and high heat. Size does matter, and smaller is better. I have found that at the end of the day I prefer my  DFL Tanto over everything else when considering size, weight, cost, availability and the fact that I have four different end caps so I can move it around guns easily. The Sumo is a little quieter but the Tanto doesn't change my poi, so the Tanto wins. Thanks for doing the review!

These are some most excellent points you bring up regarding air vs PB barrel gases. One involves actual ignition and combustion effects that are in a totally different realm when constructing “quieting-down” devices for them.

Thank You Carl!
(or should it be “Puma” Carl?) 

[Rallyshark]

Thanks for the detailed comments Donny. I too would like to test on true bare barreled guns, but the only one I have is an Evanix AR6K which makes a consistently moderate noise from where the air escapes between the pellet cylinder facings and the breech when shot, which does seem to affect the sound meter readings when I trialed it briefly before settling on the Avenger.

Oh well...

As a beggar, I can't be a chooser   I appreciate all the testing you were able to do!

Naw, you could just loan me all your bare barrel guns, Haw!!! 😉

If I had one I wasn't using, I would!  Unfortunately, they all have a job to do    

[mrbulk]

Naw, you could just loan me all your bare barrel guns, Haw!!! 😉

If I had one I wasn't using, I would!  Unfortunately, they all have a job to do

You sir, are a true airgunner indeed. *Salut!*

[Long_Gun_Dallas]

  Even more so, a bare barreled high powered gun will really test an LDC  

I've been running a huma mod 30, albeit a long version of it on the 14.25" .22 barrel I got from you.  34 fpe on such a short barrel I know takes some serious air volume to achieve.  And the mod 30, even running loose baffle bores (7mm)  is whisper quiet.

That's 4 40mm chambers and 2 20mm.

It's actually so effective,  weight and sound wise, that it's actually bordering on negating the use of the functional shroud I have for it (with internal tight-bore air stripper).  I can get less sound with less weight without the shroud, but more length.

Charlie, if you have any interest in testing a mod30 and the modified fx moderator I have, let me know.  I'm interested to see how they stack up