DIY parts moderator first attempt. An experiment.

[Richiew]

I bought these bits off Aliexpress a little while back. They were advertised as "Moisture proof pipe". Totally mis-described, as there's a 1/2" 20unf thread in one end and an 8mm hole in the other. There's also six vent holes for some reason. The tube is 31mm OD 28mm ID and 230mm long. The total cost of the three came to £34.52

Someone else on here also bought some of these before they disappeared off Aliexpress. A comment was made that the 1/2" 20 barrel thread was rather slack. This is the case but it seems OK to me once screwed up tight. I think this end may end up getting drilled out, and a threaded bung put in to remake the thread. It could also do with some material removal, as there's lots of unnecessary mass.



This is it dismantled. You can see the vent holes showing in the tube in the background if you look carefully. The tube just needs baffles and the usual sound deadening material.





I already own a Hogan Decimeater. This is a stock photo of one dismantled below. Two baffles sandwiched between three milled tubes which are covered in felt. Initially I thought it would be a good idea to copy this.




Some aluminium was purchased, and a start was made. I did a little bit of very shoddy milling and turning as an experiment. Yes, I know the tube end shouldn't be unsupported but it was just brief test to get my eye in, so to speak.



This turned ally part is used to keep the slotted tube concentric, this part was made for a differently dimensioned Aliexpress tube that I'd also bought. The slotted ally tube was to be used in both, so it's still pertinent to the project here.









Weight started to become a consideration with all the ally parts mounting up. I bought some thinner walled ally tube. The slotted part above was 1.5mm wall. I wanted to remake it in 1.2mm wall. Ideally we don't want a hefty lump hanging off the end of the barrel. A little more research was done and I ended up going a different direction.


Continued.....

 

[Richiew]

So after starting with an old school machining build I started reading up about hair curlers being used in DIY moderators. They are super light already, perforated all over, cylindrical. What's not to like? In keeping with a plastic build I thought about 3D printed baffles, expecting them to be lighter than ally and less effort to create.

This is my plastic baffle drawn up in fusion 360. 28mm OD to match the ID of the tube. The smaller outer diameter step is 18mm to match the ID of the curlers. The through hole is 6mm as my rifle is .177" or 4.5mm bore.







This is my set-up. First iteration. I had to cut one curler short. The arrangement is slightly too long which creates compression to keep everything tightly in place when the threaded end is screwed down.




This is the curler in the barrel. It's nice fit snug fit so there's no room for any felt material around the outside. These curlers come in different sizes so I'll look to buy some smaller ones to give me some clearance. I bought these off Ebay for £4.95. There's a chain of shops called Boyes in my part of the country and they sell them much cheaper.



Time for a test

 

[zedd]

Looking at the shan bao stuff on ali express
They also sell regulators , cylinders etc
So with the right mi dset you could probably put a pcp together for under £100

 

[Richiew]

The TLDR version is, it works.

To my ears, it is just as quiet as the Hogan Decimeter. This moderator is 50% longer however, so it's currently less efficient. The first thing I'm going to try is to cut the two full curlers in half and add extra baffles that I have going spare. As mentioned previously, some smaller diameter curlers will be tried which should leave some room for felt as well.

The moderator has been tested on my sub 12 Reximex Lyra. I started off just dry firing from the hip and listening. There's no point holding the stock to your cheek as you just get the mechanical noise and vibration through the stock.

Next up, a sound meter app downloaded for a little bit of objectivity.

I set up to shoot a target off my Primos Sticks. I placed an upturned bucket on the ground about 1meter from the end of the gun for the phone. The gun was fired from a seated position, so the sound meter was a bit lower than the gun. I'm not sure how well the sound meter app picked up the noise but the figures sort of reflect what I'm hearing.


This is the Hogan Decimeater, five shots. Five peaks are shots followed by, I presume, reloading noises each time. There's some final noise as I trundle towards the phone to press pause on the data capture. Max 76.2



This is 3 shots with the homemade moderator. The graph shows some reloading noise at the start. Three shot peaks and reloads and finally noise from me approaching the phone. Max 76.6. If you look at the graph, the second and third shots are quieter.





I took one unsilenced shot. Very loud indeed. I didn't want to repeat it as I try to keep this hobby under the radar with the neighbours. I don't think the sound meter is doing justice to the noise to be honest. I expected a higher figure. Was left under no illusion that the moderator is doing a job.

The first graph peak on the left is I think me knocking the plastic chair as I sat down. The shot peak is the big one at around 22 seconds. There's the reload before it and some noise at the end as I approach the meter to press pause.




This one below shows another test with the DIY moderator. I didn't want to use it, as a plane flew overhead as I was shooting. The peak figure is about the same, I think the jet engine noise made the graph less distinct. This is why there were only 3 shots for the comparison used above.





It's been a fun experiment so far. There's still much more to try in making it quieter and lighter. I might even get some proper lathe work in by the end of it.

 

[Richiew]

Minor correction to one of the dimensions mentioned. Tube ID and the associated baffle diameter is 26mm, not 28mm.

 

[Richiew]

V1.1 set up, ready for testing tomorrow, weather permitting.


The important thing is to cut the ends square, or file them back square afterwards, so everything stays straight.

Anyone know any good sources for suitable felt? There are loads on Ebay but I think I need a loose weave to let air move through?
Not sure what's suitable and what isn't. Was also thinking about removing the green velcro like hoops on these rollers to make room for felt. I don't think they do much sound deadening as they are.

 

[Balders]

Well done. Looks like you're having fun.
I got a variety pack of crafting felt from eBay. Mine is quite a dense fabric.
Get rid of the hooks on the curlers they're only serving as a centralising spacer in your tube.
Keep playing, it's a good way to learn

 

[Balders]

Here's the gubbins inside one of my shrouds. You can see the thickness of the felt. Tesco's hair curlers

 

[Richiew]

Cheers for that, Balders. The hooky loopy bits are about 2.5mm high as best as I can measure so I can probably manage 3mm felt at a push. I see you got around the issue of cutting fine internal threads with a bung and grub screw arrangement. Mine were pre-cut. I think I'd struggle if I had to do it myself.

 

[Balders]

I made the ends and got them anodised. 3mm tap jobbie

 

[Richiew]

Took a chance on some 3mm Ebay felt. See how it goes.

 

[Beaver]

Tidy job

 

[Brooksy]

In my experience it's best to use thinner curlers, keep the hook and loop on them and then use the fluffy microfibre cleaning cloth instead of felt.

 

[Richiew]

Thinner curlers are definitely on the to do list. The place I'm getting them from will do the cloths as well. Thanks for the suggestion

 

[Brooksy]

Thinner curlers are definitely on the to do list. The place I'm getting them from will do the cloths as well. Thanks for the suggestion

These are the best, they're quite strong and don't crush. https://www.ebay.co.uk/itm/16209518...uY3+MwVs=|tkp:Bk9SR8b9-8naZA&var=461055609199

 

[Richiew]

Tried the extra baffled version today. The extra baffles don't seem to make any difference, either to my ear or the meter.

With 20/20 hindsight, this is perhaps not surprising. The commercially made one only has two baffles and I presume the makers did a little more testing and development than I have.

I tested two strings of five shots. I limit the tests to five shots as I can't get the graph to show more than 30 seconds of data. The sound meter app is very limiting and frustrating. There doesn't seem to be anyway to save or interrogate the data. All the free apps I've looked at are pretty much the same. I also think there's too much variability in the small samples to measure meaningful differences.

The max figure reading isn't a particularly useful measurement either. In the screenshot immediately below, the first shot is the highest, the following four shots are lower by a fair margin. I suppose I should try for the best and trust my ear. I'm still not convinced the microphone is picking up sufficient noise signal.

Felt, microfibre and smaller rollers this weekend.

 

[Brooksy]

To go five or six baffle, you need to increase the baffle gap by approx 25% each time. Example, first 18mm, then 22, then 28, then 35, ending with 42mm. Those are Bucketboy specs that I followed and it was superb. Also, keep the holes in the baffle plates as close to the calibre as you dare.

 

[Richiew]

Great info. Thank you. I'm at 6mm for the holes, no clipping or anything but I expect I'm close to the limit.

I think I have most of the crack from the barrel eliminated. It's hard to tell, I need som one else to fire it while I listen from a little futher away. I think most of the remaining noise is from the mechanical end.

 

[sbd]

Apologies if teaching my grandmother to suck eggs but in terms of measurements remember that the decibel scale is logarithmic.

sbd

 

[Richiew]

No apology needed. I know that 80 is twice as loud as 70 etc. I just don't trust the measurements I'm getting. Kicking a plastic chair is apparently as loud as an unsilenced air rifle. It isn't to my ears. Perhaps the problem is that the noise from the shots is so brief that the microphone and meter struggle to measure?