Evanix Rex reflex inserts for shroud

[Mr.P]

Well here’s the Rex p with a shroud sleeve and that short baffle core I posted earlier.

This thing is loud - we will see if this makes a noticeable difference, I am not happy doing my breath. I also added a see-all sight, which I’m still trying to decide if I like or not on this air gun.

EDIT:  proto type failed - some layer in the wall of the baffle section separated (no shattering of anything), launched the baffles which landed about 2 feet from the target 25 m away.  Quite a bang.

I am re-printing with thicker walls that taper towards the front.  I probably went too far the other way now…

[Clicky]

I paid 4k for a stand alone license for Solidworks 2015.  Until it is unable to do what I need, I think I have spent enough.  I have more time than money...

No need to spend more, just go with the free version

In addition to the default *.f3d, export also has: *.3mf, *.ipt, *.fbx, *.obj, *.skp, *.smt, *.stp/*.step, *.stl, *.usdz

You have to buy a license to get *.dwg, *.dxf, *.igs/*.iges, *.sat

[Clicky]

Well here’s the Rex p with a shroud sleeve and that short baffle core I posted earlier.

This thing is loud - we will see if this makes a noticeable difference, I am not happy doing my breath. I also added a see-all sight, which I’m still trying to decide if I like or not on this air gun.

EDIT:  proto type failed - some layer in the wall of the baffle section separated (no shattering of anything), launched the baffles which landed about 2 feet from the target 25 m away.  Quite a bang.

I am re-printing with thicker walls that taper towards the front.  I probably went too far the other way now…

You're a step ahead of me, but I'll heed your experience accordingly! - at the moment, my threaded bushing goes on backwards perfectly fine, but it's cross-threading when I try it the right way around. I'm going to delete the rear portion of the threads because I can't run those in with the part on backwards, it bottoms out before it gets that far. Today I'll just cut the threads off on the 1st one with a lathe and see if that fixes it. I'm still planning on making the rear bushing out of aluminum, but that requires taking the barrel out so I can cut off a small flange. So until I get the front ready for testing, I'll just stay with the plastic rear just to hang the new tube in place

I have my SeeAll on a riser block set all the way forwards on the rail, and I put the reservoir under my cheek just like a cheek rest on a rifle. It works really well like that, the sight picture is perfect and the hold is much steadier on target. I'm getting inside one MOB (minute of beer can) at 50 yards

I cut an index mark into the SeeAll adjuster screws. But I keep forgetting which way they turn. I have the 1st gen version, which is opposite, and the company never thought it was necessary to indicate how to sight in. It was never intended to be used as a target sight, which is a shame because the sight picture is so much better than any other open sight. I'd like to find a riser block that has proper windage & elevation adjustments. But it might be better to just print one

[Mr.P]

I appreciate your comments on the see-all as I have been trying to figure out where it would work best.  I am going to try what you describe l because the Rex P hardly lends itself to a normal pistol hold and like you I end up doing a little mini carbine hold that is steadier than anything else I can manage. Having the gun close makes the “delta” appear pretty small, which actually
isn’t so bad for a couple of reasons, but I feel it is maybe a little smaller than practical or intended with the sight up close.

On the mark 2 they have a little arrow to show which way to turn the windage adjustment.  For elevation I know clockwise raises impact point.   

Minute of beer can at 50m with a rex p open sights sounds pretty danged good to me.  I’ve just barely got it sighted in but I doubt I could pull that off.  Would be fun to try however!

[Clicky]

I appreciate your comments on the see-all as I have been trying to figure out where it would work best.  I am going to try what you describe l because the Rex P hardly lends itself to a normal pistol hold and like you I end up doing a little mini carbine hold that is steadier than anything else I can manage. Having the gun close makes the “delta” appear pretty small, which actually
isn’t so bad for a couple of reasons, but I feel it is maybe a little smaller than practical or intended with the sight up close.

On the mark 2 they have a little arrow to show which way to turn the windage adjustment.  For elevation I know clockwise raises impact point.   

Minute of beer can at 50m with a rex p open sights sounds pretty danged good to me.  I’ve just barely got it sighted in but I doubt I could pull that off.  Would be fun to try however!

Well, you have to re-air for each shot when shooting like that. I wish I had a regulated bottle for tethered shooting. And I'm using the FX hybrid slugs, which are very consistent & really nice for distance

It also helps that I worked on the trigger group. The pull is very smooth and much lighter than it used to be. I also rounded off the sharp edges on the face of the trigger so it fits nicer without distracting me. I added an insert at the front of the hammer spring to center it on the barrel, polished the outside contact areas on the spring and the inside of the hammer where the spring touches. That makes re-arming the hammer very smooth & the shot cycle is also smoother

I have the 2nd gen SeeAll, with the range compensating reticle. The windage marking is very hard to read. The triangle portion of the arrow barely looks like anything, so I have to keep reminding myself that it doesn't make sense for it to not be pointing away from the letter 'R'

In my Bulldog, the FX slug is dialed in at 30 yards and stays pretty flat from 20 to 70

[Mr.P]

“ I added an insert at the front of the hammer spring to center it on the barrel, polished the outside contact areas on the spring and the inside of the hammer where the spring touches. That makes re-arming the hammer very smooth & the shot cycle is also smoother”

I have two rex receivers, one came with the Rex rifle and the other with the Rex p.  The action on the pistol is much smoother, very nice smooth clicky feel like a well oiled machine.  The rifle is grittier feeling, and maybe centering the spring would be a good fix.  I’ve noticed that it’s smoothing out with time and I think it may just be that the pistol that I bought had been shot  more times than the rifle.  Got them both second hand…

[subscriber]

I am re-printing with thicker walls that taper towards the front.

That's the ticket.  Add strength where required.

[Clicky]

“ I added an insert at the front of the hammer spring to center it on the barrel, polished the outside contact areas on the spring and the inside of the hammer where the spring touches. That makes re-arming the hammer very smooth & the shot cycle is also smoother”

I have two rex receivers, one came with the Rex rifle and the other with the Rex p.  The action on the pistol is much smoother, very nice smooth clicky feel like a well oiled machine.  The rifle is grittier feeling, and maybe centering the spring would be a good fix.  I’ve noticed that it’s smoothing out with time and I think it may just be that the pistol that I bought had been shot  more times than the rifle.  Got them both second hand…

Best to skip all the shot cycles and polish the works right up front

I just took the pistol apart so I can cut the flange off the barrel bushing. The spring insert goes outside of the spring for centering, there's not enough clearance to have it on the inside of the spring. I'd forgotten, but I needed to take out a ton of slop. I'm not sure if a spacer was missing, or if the spring is shot, but it wouldn't fire at full pressure on the high power mode. My hammer spring spacer is about 38mm. The spring looks normal. It's free length is 104.5mm

I've been thinking about adding a regulated tube tank under the barrel, run a hard line back to the reservoir. I'd like to have the air line connect at the front of the reservoir. Then make a piston to go inside the reservoir so that the rear portion of the reservoir is a air-spring for the piston. The idea is to avoid a large pressure drop during the shot cycle until the exhaust valve can close. I think the hard line might require a metering jet so the front tank isn't wasting air

On the full-size Rex, I would place the main tank underneath the old tank and then the air connection could be a lot simpler

[Mr.P]

Two things:

1) you mention an insert / spacer for the spring.   You added this to add more compression to the spring correct?  Are you doing this just to get the valve open at 250 bar, or are you trying to squeeze more power out of the gun?  Also - how old is that spring?  I know if you dig you will see people found various non-standard springs for this gun to replace the hammer spring.  I am sure there is some risk of deforming the valve stem if a really heavy spring is added…

2) you mention your hammer was not hitting hard enough to open the valve all the way at full pressure.  Does this tank have the stainless finish on the air cylinder near the top hat or does it have the darker blued finish?

I have one of each tank type and the silver one (which is newer) is harder to knock open for sure.  When I first got it it was pretty much valve locked if I topped it off.  It would shoot, but very underpowered for 1-2 shots.  That’s no longer the case - something has smoothed out or broken in and now I get what feels like good power at 250 bar. I have not yet done any meaningful shooting over a chronograph with these evanix guns. 

[Mr.P]

I am re-printing with thicker walls that taper towards the front.

That's the ticket.  Add strength where required.

This one works!  Makes the Rex P much less noisy.  Still loud, but I don’t feel a need for ear protection so that’s good.  I can see a couple of areas to improve the seal in the shroud and will likely make another iteration of this even though it’s good enough. 

[subscriber]

I'd like to have the air line connect at the front of the reservoir. Then make a piston to go inside the reservoir so that the rear portion of the reservoir is a air-spring for the piston. The idea is to avoid a large pressure drop during the shot cycle until the exhaust valve can close.

Unless you use a stepped diameter piston, you already have what you want without the piston - the air in the plenum is its own air spring.  The best thing you can do is make the plenum volume larger, so that the pressure drop during the shot cycle is less.

If the air spring piston area is 10 times that of the bullet base, the piston has to accelerate and reach velocities approaching 1/10 that of the bullet.  The piston has much more inertia than the bullet, so it lags in acceleration; then does not want to stop.  The piston seal also has friction.  Make a larger plenum as close to the valve as possible...

A sweeper piston has application in a SSP (but find one that is still on the market).  In a PCP that expels only part of the plenum volume per shot, a larger plenum works better to maintain pressure during the shot, and is way less complicated.  Yes, I have thought about this before....

[Clicky]

Two things:

1) you mention an insert / spacer for the spring.   You added this to add more compression to the spring correct?  Are you doing this just to get the valve open at 250 bar, or are you trying to squeeze more power out of the gun?  Also - how old is that spring?  I know if you dig you will see people found various non-standard springs for this gun to replace the hammer spring.  I am sure there is some risk of deforming the valve stem if a really heavy spring is added…

2) you mention your hammer was not hitting hard enough to open the valve all the way at full pressure.  Does this tank have the stainless finish on the air cylinder near the top hat or does it have the darker blued finish?

I have one of each tank type and the silver one (which is newer) is harder to knock open for sure.  When I first got it it was pretty much valve locked if I topped it off.  It would shoot, but very underpowered for 1-2 shots.  That’s no longer the case - something has smoothed out or broken in and now I get what feels like good power at 250 bar. I have not yet done any meaningful shooting over a chronograph with these evanix guns.

My gauge red lines at 200 Bar, I've never had it at 250. The end of the tank is marked 'Max 220 bar 2017-05', and I have gone up to 220

Dark blued steel. I've had the exhaust valve apart several times and the valve spring is the one thing where results could vary, assuming the pressure gauges are all reasonably the same. The way it's assembled doesn't allow accidentally altering it's compressed length. The spring keeper is supposed to be firmly bottomed out and the dimensions of all those pieces should be the same from one batch to the next. But purchasing spring wire, winding technique, heat treating, and a few other things could introduce changes without spotting the difference on assembly

I would bet the valve spring may have settled in a small amount. Next time you have that issue, try swapping the spring with one off a tank without that problem

I have a couple chronys, but they have a few issues

There's something else I did with the Rex hammer spring. Springs like to rotate when they work. So I re-shaped & polished the ends so it can do that without binding. It was cut crudely and very casually finish ground, like someone was only concerned with deburring

I checked the amount of bind on the hammer spring, and I have it set with lots of room between coils

The cocking effort is very low, just a few pounds. I've never felt that it was 'difficult' after adding the spacer

[Mr.P]

Huh… both of my guns specify 250 bar maximum fill.  Must be a change from early models.

[Clicky]

Huh… both of my guns specify 250 bar maximum fill.  Must be a change from early models.

I'm sure there's a long back story on it. If only the factory workers were on this thread

I think the example I have is better than when I first got it. But it would be nice if we were to meet at a range & compare the two

It's possible that if I were to get a new valve spring, that my spacer wont be needed

If the valve spring is changed such that it has greater closing force, the result will be that the same fill pressure will be too high

The opposite should be true. If the newer springs are much less in closing force, then the fill pressure could be higher

And, if some old springs get mixed up in the new production, results can be random

This is why I prefer dump valves with a plenum charge valve that only opens when the exhaust valve is reset

[Mr.P]

Did some more testing of the Rex P,  The simple modification is well worth the effort!  Happy to provide the files for anyone who wants to print their own but it is such a simple 3d model to design - anyone with a printer and basic tinkercad could whip up something like this in short order. 

Now I’m looking at this and even though I have achieved “good enough” I’m wondering if maybe adding another inch or two (and another chamber) to the baffles would be a good idea.  I also like subscriber’s thought about having a tapered bore - with closer tolerances closer to the muzzle where any angular deflection has had less time to accumulate. 

I wonder what principles as far as baffle spacing, number, angle, etc. would let you get the most back pressure from a skinny short ldc like this, and if my ear could even detect the difference between crude and more sophisticated designs. 

Also for what it’s worth for these projects I’m trying to mainly use the shroud and avoiding screw-on solutions altogether for a couple of reasons.  First, it presents a challenge, and working under constraints like this and trying to work around them is good entertainment.  Second, screw on devices exist in some legal gray area it seems, and even though all I shoot / own are airguns it seems wise to have all of my noise reduction projects being built in the shrouds when possible or with customized shrouds that are adapted specifically to the airgun and effectively built-in when installed. 

[Clicky]

Did some more testing of the Rex P,  The simple modification is well worth the effort!  Happy to provide the files for anyone who wants to print their own but it is such a simple 3d model to design - anyone with a printer and basic tinkercad could whip up something like this in short order. 

Now I’m looking at this and even though I have achieved “good enough” I’m wondering if maybe adding another inch or two (and another chamber) to the baffles would be a good idea.  I also like subscriber’s thought about having a tapered bore - with closer tolerances closer to the muzzle where any angular deflection has had less time to accumulate. 

I wonder what principles as far as baffle spacing, number, angle, etc. would let you get the most back pressure from a skinny short ldc like this, and if my ear could even detect the difference between crude and more sophisticated designs. 

Also for what it’s worth for these projects I’m trying to mainly use the shroud and avoiding screw-on solutions altogether for a couple of reasons.  First, it presents a challenge, and working under constraints like this and trying to work around them is good entertainment.  Second, screw on devices exist in some legal gray area it seems, and even though all I shoot / own are airguns it seems wise to have all of my noise reduction projects being built in the shrouds when possible or with customized shrouds that are adapted specifically to the airgun and effectively built-in when installed.

You should try bumping up to a 2", or just something larger. Maybe shape the LDC so it works better as a fore grip. Adding volume rearwards should give better results than adding length will

That's a good point about not having the detachable aspect interfere with the legal status. I imagine DonnyFL must be pushing the boundaries with his products! All of the DonnyFL LDC's have markings to indicate that they are for airgun use only. Should all of these prints include such markings?

For measuring your results, wouldn't it be good enough to just record video in a manner that keeps the microphone physically consistent in it's location from the muzzle? I don't think you need to know the true decibels. Just having a repeatable sound level that you can use to verify if it's going up or down should be good enough. If you see the sound level get cut in half, that's a meaningful result

Plus it's possible to get a fair approximation of your velocity if the video is recording a target strike. For that, I would shoot at both 10 & 50 meters

So far, I've cut the flange off and am planning on keeping the rear puck in place with bearing retaining compound. Last night, I cut a section from a flat bar for my rear puck, so today I'll be swapping in the 4-jaw chuck to bore that out. I ought to take a few breaks so I can take pics. A good reason to have my real camera, as it's less fiddly to work with

[subscriber]

Marco,

What about stepping up the diameter of the forward section to match the outer tube, at the same length you have it now, or with your added 2"?  See crude sketch.

Asking what will reduce sound for a given narrow short baffle volume has to also ask what the side effects ight be.   Other than clipping from the narrowest section of baffle bore being too tight, it is also possible to induce aerodynamic steering: 

This is where barrel vibration causes the moderator section to move laterally before the projectile is out.    The pressurized air can form an air bearing that tries to center the projectile in the "tube" to even out the leak path, thus causing the projectile to deviate from the path it acquired in the barrel.  The risk of this happening goes up, if the parallel bore section of the baffles is both tight and long.

Why would you make the parallel bore section long and tight?  Because it reduces air leaking past the projectile, thus reducing report.  At the risk of steering the projectile.   How does one reduce the risk?  Open the bore first, because the parallel length affect the length of time that the projectile acts as a plug, while the bore affects how leaky the plug is.

Making the parallel bore or spigot long creates space for the air to go as the projectile enters the baffle bore.  It also places the leading edge of the baffle bore closer to the muzzle, or to the exit of the previous baffle bore.  Having the first air stripper cone edge near the muzzle works because the air pressure there is the highest (after projectile uncorking from the muzzle).   Also, shielding the projectile from buffeting near the barrel muzzle is good for tighter groups.   

The higher the pressure, the more air wants to flow radially off the bore line.   As the bulk air pressure drops its forward momentum becomes more important.   Thus the air takes on the shape of a more columnated jet.  Such a jet tends to flow straight down the baffle bore more directly, and makes cone lips placed close to the baffle exit (or barrel muzzle) less effective at  diverting flow.  This effect exists at forward baffles because the average air pressure there is lower (the whole idea).  The effect also affect the effectiveness of the first baffle cone or air stripper, as the pressure decays from the barrel muzzle. 

The latter may matter less because the loudest noise comes from the peak muzzle pressure immediately after the projectile exits the muzzle.  This is where the downstream air stripper cones do more work.

I mentioned Matt Dubber had a suppressor that tapered to provide more radial space near the barrel muzzle and less further forward.  He just happened to use it in a video he posted yesterday.  I grabbed an image of it - see below.

I mentioned before that there are many overlapping principles at play and that there is no one best way to design a LDC.  Taking a good principle too far can make the device less effective:  The number 4 sketch below has a very long parallel tube, place very close to the barrel muzzle.  It would allow a lot of air to follow he projectile straight down the tube because there is only one narrow path between air stripper and barrel muzzle to divert air into the body of the LDC and potentially the rear of a shroud.  Breaking the long tube up into several stage with more radial vent area would be more effective, despite shortening the parallel section of the inner tube.  The later would also have maximum potential for steering the projectile aerodynamically.

How long should the parallel section of the air stripper be?  One half to two calibers should work well enough without causing trouble.  The tighter the bore to projectile radial clearance, the shorter the parallel sections should be, or expect more fliers on target.  A radial clearance of 1 mm is good, while 0.5 mm is asking for trouble.  More than 1 mm clearance is better when there is uncertainty about alignment, and to allow for sideways motion of the moderator while the projectile is moving through it.  Or, yaw of the projectile for that matter.

What about the other sketches?  # 1 is a better geometry for the first air stripper near the muzzle.  #2 is better for later stages where the pressure has already dropped.  #3 avoids a excessively long parallel path, but in a narrow LDC tube, reduces the forward air capacity (green bars).  So, a whole bunch of interdependent factors at play.

How large should the first chamber be?  For PBs the first or "blast chamber" is usually 1/3 of the total expansion volume, simply to lower the bulk gas pressure immediately.  This is so that a thinner wall outer tube can be used without bulging it.   Reflex shroud volume on a PB or airgun allows the first baffle volume in front of the muzzle to be smaller.

Then why do we see so many airguns with all the baffles exactly the same "medium" length?   Cheaper to manufacture and simpler to install.  A reasonable compromise where more length can be added, if more sound reduction is required.

Your latest design is approximated by #5.  I suggest #6 may be better suited.   Place the air stripper closer to the barrel muzzle, but grow it out of a tube with a 3 mm radial clearance on the projectile diameter.  That way, the distance  between the first and second cone is greater, which makes more sense to allow the now lower pressure air to spread more before reaching the second air stripper lip.  While you are at it, make use of the potentially larger nose diameter on your "insert", without it looking like a pickle.  Or, perhaps, you prefer the stock .50 BMG look, with a smaller barrel pocking out of a "heat shield".  You could make the nose section of your insert larger in diameter, short of matching the heat shield diameter...

[Mr.P]

Lots of good stuff to digest! 

A couple of replies:

1) The diameter projecting beyond the shroud is determined by the collar that is retaining it.  There is a collar that screws into the end of the outer tube and it has to slide over the projecting tube. The photo attached should clarify. 

2) I had the baffles much closer to the muzzle on my prototype and the plastic split at the first chamber. When it exploded I made two changes - thicker walls and moved baffles away from barrel to allow more room for air to expand.  Same rationale as a large expansion chamber in powder burner ldc’s.  The plastic is fragile compared to aluminum and it seemed like a good idea to alleviate pressure.  Attached is a view of the design with the additional baffle.

I just printed a longer one with an additional baffle and chamber otherwise of similar design.  Adds an additional 2 cm to the length and cut sound down quite a bit compared to the first (non exploding) model. 

I will incorporate some of your ideas into Mark 3 before printing it and share whatever the result is here. 

[subscriber]

Looks good to me, Marco.

The  small ID does not allow for a long spigot on the first chamber, so what have is as good as can be made in the available space.

[Clicky]

Little bit of progress today. Practicing the art of pounding square pegs into round holes