Choosing the correct size moderator

[cavedweller]

I currently do not have access to a quality sound meter thus my question:

Will the use of an oversized or bigger caliber moderator create a noise reduction benefit or is it just a waste.
Example high flow thunder ordnance.30 in a .177 application.
Would the same oversized moderator improve airflow behind the pellets?

 

[Smok3y]

Larger caliber hole than needed should make it louder. That is why they make all the different sizes. Otherwise, they would just make ‘em big to accommodate everything and carry less inventory.

That being said, most of the time, the difference is extremely minor.

 

[JungleShooter]

If you go up one caliber size, you're still getting pretty good sound damping — DonnyFL recommended me buy a .25 silencer for my .22 PP700 — to make sure the huge Chinese machining tolerances on the gun won't cause clipping.

Now, a .30 silencer for a .177 gun is a different story. I'm pretty sure you'll get some sound damping. But the hole is c. 70% larger than the pellet....

Matthias

 

[Lewis]

You may be surprised just how good that .30 is on your .177. The difference for me was minimal enough that I now only buy .30 cal moderators. I can use them on anything without concern of clipping etc. If I were shooting indoors or needed to be quiet enough to shoot in an urban backyard without bothering anyone then every little bit matters. In those cases though, you are likely shooting at much lower power levels, which are quieter by nature to start with.

 

[sonnysan]

You can purchase a sound meter on amazon for $20. Worth every penny with it comes to airgun discharge.
As for STO, I'd go with the 177- 30 with high flow UNF 1/2x20 Sarissa. This way you can put it on anything from 16FPE - 160FPE. You never know when you are going to up the ante on FPE. I currently have a STO Plenum on a DAR .22 30FPE. Bottom of the barrel STO LDC, but it is very effective. I do have a Sarissa. I'll eventually try that on a .25 100FPE Sumatra, then a .30 160FPE AEA just to see if it can handle the power. You can always email STO on a given applicaton. They have responded to my inquiries, and all my STO LDCs came from the used market.

 

[AlanMcD]

I agree with Lewis - I specifically bought a .30 cal Huma 40 Compact to use mostly on .22 cal guns and it works very well. I did so primarily to use on a Huben, and it has been said that some of them do not "play well" with moderators, in terms of accuracy. So the .30 was to help prevent any issues - but it sure quiets things down even with the big hole.

That said, I'm sure it would be quieter if it was a .22 cal model, but probably not by much.

Something to think about: it is in the moderator maker's best intersts to have people "want" to have their LDCs be as specific to each gun as possible, as it leads to more sales volume. I think one good moderator in .30 cal could serve many guns . . . including .177 cal ones.

 

[Gerry52]

I have a .30 Ronin. I use it mainly on my FX Boss (.30) but if using it on my .25 Royale or my .22 Bobcat (already QUIET guns) it's amazing how much quieter they are.

 

[OldSpook]

I currently do not have access to a quality sound meter thus my question:

Will the use of an oversized or bigger caliber moderator create a noise reduction benefit or is it just a waste.
Example high flow thunder ordnance.30 in a .177 application.
Would the same oversized moderator improve airflow behind the pellets?

Hi;

A caliber specific moderator of the same design will be quieter than one which is not caliber specific. It will also be more likely to clip because the tolerances are tighter.

A high flow moderator of the same design will be louder than one which is lower flow. This is simply because the more air it passes the lower the pressures are inside the moderator and the lower those pressures, the less sound reduction you will observe.

But you asked the $64.00 question also. Will a high flow moderator improve airflow behind the pellets. The answer to that one is, "If the designer did his job." Not very helpful but it is what it is. Usually a high flow design which is acting like a stripper WILL be more accurate. A high flow design which is not stripping air away from the projectile path will most likely be less accurate.

Two moderators of the same design, the one with a larger internal volume will be quieter than the one with a smaller internal volume.

Two moderators of the same baffle design, the one with the more baffles will be quieter than the one with less baffles.

The only way to compare two moderators of different designs is by physical testing (or computer modeling).

HTH
Mike

 

[subscriber]

It is not the moderator bore being large compared to the pellet that matters, as much as the moderator bore, compared to the moderator OD (or ID of the outer tube, to be more exact). The question is what percentage area of the baffle "wall" do you have left, when you make a large hole in it? So, strictly speaking, larger calibers require larger diameter moderators. There is a lot of leeway, due to the effect of the shape of the air strippers inside. Long cones are much more effective than flat walls in a small ID outer tube, for example.

I design custom moderators with baffle bore diameters that are 2 mm larger than the pellet diameter, at the first air stripper. Then increase the baffle bores along a line 1/4 degree per side larger, towards the front. So, depending on length, the muzzle end can have an "oversize hole". A moderator that is 2 dB louder is much less annoying than one that groups erratically, due to slight occasional clipping. Never mind events that chip the air strippers in an obvious manner.

 

[OldSpook]

It is not the moderator bore being large compared to the pellet that matters,

Yes it is. Build one with an exit hole that is 1.5mm over caliber and test it. Then drill it out to 2.0 over caliber and test it again. Then drill it to 2.5... etc. You will prove it for yourself.

as much as the moderator bore, compared to the moderator OD (or ID of the outer tube, to be more exact).

Absolutely the relationship of volume of moderator (bigger diameter) to volume of air produced during a shot (bigger caliber) is obviously important and a caliber specific moderator will be quieter.

The question is what percentage area of the baffle "wall" do you have left, when you make a large hole in it? So, strictly speaking, larger calibers require larger diameter moderators. There is a lot of leeway, due to the effect of the shape of the air strippers inside. Long cones are much more effective than flat walls in a small ID outer tube, for example.

That is most likely true.. but then there is the K baffle which is a large flat baffle when viewed from the muzzle end of the rifle. They seem to work just fine. This really seems to restate the point above. Big bores require big volume to accomplish exceptional moderation.

I design custom moderators with baffle bore diameters that are 2 mm larger than the pellet diameter, at the first air stripper. Then increase the baffle bores along a line 1/4 degree per side larger, towards the front. So, depending on length, the muzzle end can have an "oversize hole". A moderator that is 2 dB louder is much less annoying than one that groups erratically, due to slight occasional clipping. Never mind events that chip the air strippers in an obvious manner.

There is a fellow on the forum who is building his to 1mm over caliber. I was building them with more clearance than that (2.5mm) but I have managed to get them down to 1.5mm over caliber for the whole length of the moderator. That is probably going to be a problem for some rifles but so far so good. I have not concluded that the bore/caliber ratio can not be tightest at the attachment on the rifle. It seems reasonable to try to make it work that way because it is easier to achieve precision when your travel distance is so much reduced.

What you said there is a true statement. Accuracy pretty much trumps everything. If it don't shoot, it don't matter how quiet it is except in very specific applications.

 

[dizzums]

id just get a quality mod that fits the gun well .. ultimately 'other gun noise' will far exceed the minimal effect of worrying about different size and shapes of the moderator itself and that other gun noise needs to be adressed .. that said, if you get a plastic mod from budcus airguns, i wouldnt expect much in the way of overall performance ..

 

[subscriber]

OK, Oldspook,

My statement that the projectile to bore clearance "does not matter" is incorrect in the absolute sense. I meant that if you want a muffler to work, there is a hierarchy of aspects, and the bore clearance is not at the top - else shooting a .177 from a .25 muffler "would not work"; and that is clearly not true.

My statement was made in the context of designing mufflers for someone else, made by a second party, and used by a third party: You have no control over important aspects of system alignment. Nor do you always know what the muffler will be mounted onto: Thin whippy barrels and long mufflers can have the barrel flex in such a manner that the muffler muzzle is no longer pointing where it was when the shot broke, while the projectile is still in the muffler bore. If the bore clearance is tight, your customer can start seeing clipping. For small calibers, a tight muffler bore can also steer the pellets aerodynamically without making physical contact. So, a tendency to see large shifts in POI, and larger groups are more common with tight muffler bores, in my experience.

I do not mean that opening up the bore clearance from 1 mm to 2 mm would have no effect on peak sound measured. I am suggesting that I happily throw away a 3dB sound reduction for a muffler, if it shoots tight groups, close to where they are expected. People don't like to make large sight adjustments with one muffler, if they don't need to with another.

Yes, I was "asking for it" with what sounded like an absolute statement; but as you know, everything is relative. For a short muffler, mounted to a precisely machined, short stiff barrel, I am willing to use a tighter bore to projectile clearance. So far, I have not had complaints about my designs being louder than expected; but I have had complaints about clipping.

EDIT: Forgot to mention that the material and manufacturing methods also affect how tight I am willing to go on the muffler bore: All machined parts from Delrin or aluminum can be made tighter than 3D printed parts, especially if the whole muffler is printed as one self-contained part, with no aluminum or CF outer tube to stiffen the assembly and keep things straight. My point was that chasing 1 or 2 dB with tight muffler bores eventually ends up being silly. Re-read the bottom of my first paragraph, directly above.

 

[Geezerhood]

I find that the moderators with a larger diameter hole through them than what would be considered ideal for the caliber I am shooting always produce tighter groups than one of the same brand made for the specific caliber I am shooting. That said I only own Buck Rail and Donny FL moderators.

 

[Jasonmc]

I have 2 tatsu moderators. 30 and the 22. There is a very noticeable difference in the 22 on my 177, it is definitely more quiet.

 

[subscriber]

Jason,

It should be quieter. The extra clearance from using a .22 rated moderator on a .177 already has enough extra clearance.

As a counter point, the Marauder is a benchmark for quiet. The stock baffles have a 5/16" bore, used for .177, .22 and .25. The reason the .177 is not loud when doing this is because it is running at lower FPE and there is less air to deal with. So, the whole system should be considered when making muffler bore decisions.

 

[OldSpook]

OK, Oldspook,

My statement that the projectile to bore clearance "does not matter" is incorrect in the absolute sense. I meant that if you want a muffler to work, there is a hierarchy of aspects, and the bore clearance is not at the top - else shooting a .177 from a .25 muffler "would not work"; and that is clearly not true.

My statement was made in the context of designing mufflers for someone else, made by a second party, and used by a third party: You have no control over important aspects of system alignment. Nor do you always know what the muffler will be mounted onto: Thin whippy barrels and long mufflers can have the barrel flex in such a manner that the muffler muzzle is no longer pointing where it was when the shot broke, while the projectile is still in the muffler bore. If the bore clearance is tight, your customer can start seeing clipping. For small calibers, a tight muffler bore can also steer the pellets aerodynamically without making physical contact. So, a tendency to see large shifts in POI, and larger groups are more common with tight muffler bores, in my experience.

Yes I have seen that in my testing as well.

I do not mean that opening up the bore clearance from 1 mm to 2 mm would have no effect on peak sound measured. I am suggesting that I happily throw away a 3dB sound reduction for a muffler, if it shoots tight groups, close to where they are expected. People don't like to make large sight adjustments with one muffler, if they don't need to with another.

I understand what you are trying to say. That does not mean everyone reading it will without some amplification. Naturally the engineer is going to opt for accuracy over sound reduction. Seems like I already agreed with that point. If it don't shoot, quieting doesn't matter.

Yes, I was "asking for it" with what sounded like an absolute statement; but as you know, everything is relative. For a short muffler, mounted to a precisely machined, short stiff barrel, I am willing to use a tighter bore to projectile clearance. So far, I have not had complaints about my designs being louder than expected; but I have had complaints about clipping.

No, I don't think you "asked for it". Makes perfectly good sense.

EDIT: Forgot to mention that the material and manufacturing methods also affect how tight I am willing to go on the muffler bore: All machined parts from Delrin or aluminum can be made tighter than 3D printed parts, especially if the whole muffler is printed as one self-contained part, with no aluminum or CF outer tube to stiffen the assembly and keep things straight. My point was that chasing 1 or 2 dB with tight muffler bores eventually ends up being silly. Re-read the bottom of my first paragraph, directly above.

Of course material matters. I think you may be generalizing WRT printed materials, perhaps more than is prudent. Delrin is a plastic. It is machinable. Many plastics used in 3d printing can also be machined to very high tolerances. That is particularly true of resin printed parts. When I am adding inserts, for example, I print the thread pattern to 1/10mm (0.004") tighter than the tap. Then, using the tap, I dress the printed thread to the exact dimensions of the thread on the insert. Then I "lube" the insert with epoxy and screw it into the tapped hole. Job done. I think that process (using the tool chain I built for the purpose) is probably as accurate as most machinists can do with any material (CNC machines excluded).

I'm sure there is a lot I can learn from you. That "steering" business you mentioned above for example confirms something I thought MIGHT be going on. What I have seen in the industry though is a whole lot of half-baked engineering which passes for "cutting edge" and sells at five or six times cost of production. That's a shame.

These two moderators: https://www.airgunnation.com/threads/dragonfly.1296704/ could be mass produced and added to every production rifle that bears that name for $40.00 per unit and the vendor would make more than $20.00 profit on each unit. So ... so it is the cost of engineering and machining which drives the cost of these devices. Reduce the cost of machining (printed parts) and you are left with reasonable prices, unless your engineer is overly impressed with himself.

 

[OldSpook]

I find that the moderators with a larger diameter hole through them than what would be considered ideal for the caliber I am shooting always produce tighter groups than one of the same brand made for the specific caliber I am shooting. That said I only own Buck Rail and Donny FL moderators.

Yep. There are two parts to building that moderator. It needs to shoot as well as the rifle without the moderator (or better) and it needs to quiet the rifle. That's hard. It is really easy to build a stripper and they will make your rifle more accurate than the same rifle without the device. It is really hard to build a moderator that will improve the accuracy of your rifle AND make it significantly quieter.

 

[subscriber]

Oldspook,

We can all learn something from each other. I like to see approaches I have not thought of; or when someone pushes past a limit I have set for myself. Even if something fails, debugging that is more instructive than having something work accidentally.

Any idea I can come up with has probably already been tried by someone else. The good ones are usually already patented. Ideas spring forth continually for me; yet I have only 26 US patents.

There are many different approaches to making airguns quieter. Some people are pedantic about what a design must have. I don't care about claims, based on it being "new and improved". I care about what the family and neighbors of the end user say about the report. The best comment is "you were shooting? I did not notice".

People can be so hung up on objective measurements that they prefer make-shift instruments or apps, that are clearly not up to the task. They may declare 5 moderator all measure the same, despite the human ear ranking some of them "twice as loud" as others. The fact that the instrument's mic is clipping at max reading, or that they are capturing the sound of the projectile slapping the trap easily escapes them; because they have "objective data". Quite frankly, I like video or sound recordings at a fixed recording level, from a distance where there is not maxing out of the range. Then listening to that a few times. Even if I am at the test site, the ability to hear a number of sound recording back to back in quick succession is useful. You can go on the analyze the intensities at different frequencies, as well as the wave form. I notice that sharp snapping sounds can be identified from the wave form, and may matter more than the peak meter reading.

If my ears, the ears of customers, and their neighbors do not agree with meter reading rankings, then I am going with the ears. Because the ears are attached to brains that can decide they don't like the noise, and want to do something about it.

Meter readings that show differences that I can agree with are still useful to me. I am not going to insist on proof of calibration, if a given airgun reads 90 dB instead of 100. So, I usually try to be polite when I see impossible readings. If the meter reads 100 db rather than an expected 85, I ask about the type of trap and how far it is from the meter. Also, if the meter is a foot in front of the muzzle, that might peg all values at the max meter reading. I prefer readings from 10 yards away, even f they are officially wrong, because they are more likely to capture the differences between moderators, closer to th e way our ears percieve them.

Except for powerful unshrouded PCPs, muffler testing on shrouded airguns is not so much about proving a system is hearing safe, as to predict how people at some distance will react to the noise.

 

[JungleShooter]

subscriber and Oldspook — you (among others) are a great enrichment to our sport and the forums — you're so much more engineers, inventors, and scientist than most of us here.
Thanks for continuing to contribute by researching, inventing, and producing.

Matthias

 

[OldSpook]

Oldspook,

We can all learn something from each other. I like to see approaches I have not thought of; or when someone pushes past a limit I have set for myself. Even if something fails, debugging that is more instructive than having something work accidentally.

Any idea I can come up with has probably already been tried by someone else. The good ones are usually already patented. Ideas spring forth continually for me; yet I have only 26 US patents.

There are many different approaches to making airguns quieter. Some people are pedantic about what a design must have. I don't care about claims, based on it being "new and improved". I care about what the family and neighbors of the end user say about the report. The best comment is "you were shooting? I did not notice".

People can be so hung up on objective measurements that they prefer make-shift instruments or apps, that are clearly not up to the task. They may declare 5 moderator all measure the same, despite the human ear ranking some of them "twice as loud" as others. The fact that the instrument's mic is clipping at max reading, or that they are capturing the sound of the projectile slapping the trap easily escapes them; because they have "objective data". Quite frankly, I like video or sound recordings at a fixed recording level, from a distance where there is not maxing out of the range. Then listening to that a few times. Even if I am at the test site, the ability to hear a number of sound recording back to back in quick succession is useful. You can go on the analyze the intensities at different frequencies, as well as the wave form. I notice that sharp snapping sounds can be identified from the wave form, and may matter more than the peak meter reading.

If my ears, the ears of customers, and their neighbors do not agree with meter reading rankings, then I am going with the ears. Because the ears are attached to brains that can decide they don't like the noise, and want to do something about it.

Meter readings that show differences that I can agree with are still useful to me. I am not going to insist on proof of calibration, if a given airgun reads 90 dB instead of 100. So, I usually try to be polite when I see impossible readings. If the meter reads 100 db rather than an expected 85, I ask about the type of trap and how far it is from the meter. Also, if the meter is a foot in front of the muzzle, that might peg all values at the max meter reading. I prefer readings from 10 yards away, even f they are officially wrong, because they are more likely to capture the differences between moderators, closer to th e way our ears percieve them.

Except for powerful unshrouded PCPs, muffler testing on shrouded airguns is not so much about proving a system is hearing safe, as to predict how people at some distance will react to the noise.

I don't really see the point of any of this relative to the OPs original question. It feels more like EPEEN waving, braggadocio and opinion than actual science.

But you seem to want to do this so lets do it.

The OP asked a simple question. I gave him my opinion. If you think there is something wrong with it, by all means point it out and correct me. I'll listen and evaluate your opinion based upon my personal experience, and if I think you are correct, I will make the necessary changes in my thinking. If I don't think you are correct, I will differ with you. What I won't do is wave EPeen with you and declare to you all of the things I have done. You wouldn't believe them anyway. What I have done, really doesn't matter all that much. Suffice it to say, I know what I am talking about because I take the time to study it before I speak on it. I don't have 26 patents, but if I did, they would not prove I know much of anything except how to apply for a patent.

I'm here to have fun and learn new things.

So thanks for the new ideas (or the ones that I already had and either opted to keep or discarded).

I am sure you are a world class engineer, you have clearly established that much in this thread. Maybe now you can start addressing the question the OP asked? As a matter of fact, start with the template I first offered to him. That will get us back on track with the thread.

I should warn you though. There is one thing which will get me going. If you publish as truth something which I can show to be false, I won't stop until I have beaten that nail through the board and time is no problem. I can and will do the math. There are several here who will vouch for that.

I hope we are done here.

I really am not here to prove anything. That is for children.