GeckoSub Mirage Evo - And Adventures in 3D Printing Speargun Parts

[Diving Gecko]

Same Ol', Same Ol'
As mentioned, I took the gun apart again (again, again), the rubber sleeve had moved rearwards on the pumping barrel exposing the first row of venting holes. Maybe from the air pushing it during use or perhaps during disassembly. I kinda hope it's the first because it would explain the latest failure

I then cut the countersinking and grooves for the sleeve a bit deeper to hopefully stop it from moving. But the wall thickness is "only" 1.5mm so that limits how deep I can go. The vent holes are still those oversized 1.5mm ones:

Then I assembled the gun again and took it up to about 27bar and so far it has survived four dry pre-loading cycles. I will do a few more during the day as I work on other stuff. And then if it still works, I may test it in the pool again. Probably against my Pathos 100 which is quite well tuned and the closest I have to a "known standard".
That said, in terms of power, even when I had to drop the pressure to ~21-22 bar in the first pool test a little while back, this gun had a lot more power than the bandgun though I didn't test the accuracy at the time. And that was even with dyneema shooting line which is more draggy than the mono on the Pathos

On Bulkhead Sizing and The Low Power Shot
Also, I want to test how much power it has on the low power setting. This is governed by the volume rear of the bulkhead so I can "adjust" that by how long I make the bulkhead. The downside of a more powerful low power shot in a Mirage system is that you need more pumping strokes before cocking and I actually thought that would be the case with the first alu bulkhead. But even with just 5 pumping strokes we are already down to ~7 bar. So, I could likely go bigger on the bulkhead volume/length, if needed. The downside of that, apart from an increase in weight, is that deeper features are a bit more tricky to machine, but the first bulkhead turned out pretty good and it's good practice for when I want to do a full handle later on.

Anyhow, I don't think I shared any "full body pics" of the gun fully assembled, yet:

On Sizing Conventions
In terms of size designation it gets complicated but if we chose the Sten as the standard, then the Mirages were actually a bit short for their size and the Predathors are actually a bit long. Back in the day, the longer of the two Mirage models was called a 100 (later on a 104). My gun (based on a Predathor 100) would be a Mirage 110/114.
(I am basing this on the lengths of the shooting barrels, I think that's the most fair)

A New Bulkhead In The Works
Spurrred on by Zahar's ideas and some of my own, I am thinking about making a new bulkhead. One that doesn't have the peg and the check valve for the pumping barrel built-in but simply has a smooth bore for a valve assembly to drop into (btw, there's no power regulator valve in these renderings):

On the next pic, disregard the finer workings of the valve and its size - it's just an older design I added for showing what I mean:

There are a few advantages with this approach:

• I can more easily test different valve designs, like Zahar's proposed mushroom type and the "o-ring valve", without having to make a new bulkhead for each change in the valve
• If I want to change to a pumping barrel with a different inner diameter, I only need to make a new valve, not a whole new bulkhead
• I can make the valves on the manual lathe which is often easier or on the CNC mill or on a combination of the two
• And finally, the bulkhead itself becomes less complicated and easier to machine on the CNC, though as mentioned the first one went quite well

As for the missing power regulator, I have an idea I want to try out. Will explain in detail another time, but in short it's based on a ScubaPro Magnum type valve "cover" with a gasket (same as in a Salvimar's guns) rather than an o-ring on a bushing. In my 2-stage version it will have a sliding venting rod inside. If I can make it work - despite being more complicated - it will solve the issue about the power regulator opening with a huge bang, it will have a decent sized cross section and overall just be a whole lot more pleasant to use.

 

[Diving Gecko]

Bang, Bang, Good On Land...
So far, so good. Once again, the pre-loading feature works - at least on land. This time, I have done about 8 loading cycles and I have pumped a bit faster, too which is probably more like what you would do in the water as Zahar pointed out. And the pumping feature still works.

I have a bit less air in it now, started with ~28 bar or so but I lose a bit every time I take a pressure reading so down to ~26 bar now.

And while I did say that in order to not put too much stress on this silicone sleeve valve, I wouldn't pre-pump too much but the last few test cycles, I have done 7 strokes which lowers the pressure all the way down to ~3 bar, haha

Also a short video showing the bang when the pressure regulator opens:


On an original Mirage with the same pressure this would be way less "violent" as the old bushing was just 7mm(?) in diameter (can't recall right now) and the one in my gun is 9mm. The latter has ~14kgf pushing on it, whereas a 7mm valve would only have 9kgf - This is with 3bar behind the valve and 26 bar in front. So, if I pre-pump less, the bang is a bit reduced.
If I take the gun up to proper Mirage territory pressures like 30-35bar things would get worse which is the main reason I am looking into a different type of valve for the power regulator.

 

[Zahar]

It should be remembered that after a shot at the minimum of the power regulator, you cannot move the regulator to the maximum position and open access of the receiver pressure to the barrel with reduced pressure! This leads to a rupture of the O-ring on the regulator rod and can lead to a diesel effect - an explosion inside the barrel!

 

[Diving Gecko]

It should be remembered that after a shot at the minimum of the power regulator, you cannot move the regulator to the maximum position and open access of the receiver pressure to the barrel with reduced pressure! This leads to a rupture of the O-ring on the regulator rod and can lead to a diesel effect - an explosion inside the barrel!

Just to clarify: If I take a low power shot, I would just reload in the shooting barrel only with the power regulator still in the low power position.

The whole sequence would be:
1). Pre--pump in the pumping barrel
2). Move the shaft to the shooting barrel to cock the shaft piston in the shooting barrel AKA "Loading"
3). OPEN the power regulator to equalize the pressure in front and aft of the bulkhead so as to be ready for a high power shot but then:
4). CLOSE the power regulator for a Low Power shot (like in a classic Sten type pneumatic, same pressure either side of the bulkhead, just less air volume for the low power shot).
5). Load again, still with the power regulator in the closed position and only in the shooting barrel like a "normal" pneumatic gun.

But I am not fully sure I understand the rest of your warning, but I am trying
I may be wrong but isn't the dry testing I have done and shown in the video - and maybe even the Mirage system - worse than the the scenario you are describing?

The Mares Mirage sequence for a normal shot would be:
1). Pre-pump (keeping min. 5bar in the rear chamber and max ~40bar in the gun)
2). Cock/Load the shaft in the shooting barrel
3). Open the power regulator

Wouldn't this be worse than opening the power regulator after a low power shot? Isn't the pressure differential bigger in the normal Mirage operation? And by extension, isn't what I did dry even worse as I didn't even cock the gun? Except, I had less pressure in the gun, so I had a ~23bar pressure differential before opening of the valve but an old Mares Mirage taken up to the maximum allowed 40 bar would have ~35 bar of differential when opening the valve after pre-pumping, no (not sure how much the pressure would increase in the rear chamber once the gun is cocked)?
What am I missing?

 

[Zahar]

1. Shot at minimum. 2 Loading the harpoon with the piston at minimum. 3 Setting the power regulator to maximum. This is the correct sequence! 1. Shot at minimum. 2 Setting the power regulator to maximum. 3. Loading the harpoon with the piston. This is the wrong sequence! Pumping up the power with the second barrel should be done with the power regulator at maximum!

 

[Diving Gecko]

1. Shot at minimum. 2 Loading the harpoon with the piston at minimum. 3 Setting the power regulator to maximum. This is the correct sequence! 1. Shot at minimum. 2 Setting the power regulator to maximum. 3. Loading the harpoon with the piston. This is the wrong sequence! Pumping up the power with the second barrel should be done with the power regulator at maximum!

I agree with the right sequence.

But I don't understand this sentence:

Pumping up the power with the second barrel should be done with the power regulator at maximum!

In the Mirage system, when pre-loading/pre-pumping with the smaller barrel, the power regulator has to be closed, otherwise, you can never build a pressure differential.

In your previous post, it sounded like you said that if I open the power regulator when there's a big pressure differential there can be an "explosion" inside. But with the Mirage system, I think there will always be a big pressure differential when you open the power regulator.
Maybe I misunderstood, the translation is a little bit tricky.

 

[Zahar]

Why create a pressure differential when reloading with a second barrel? This is unnecessary and harmful! Reloading with a second barrel must be done at the maximum power regulator so that there is no pressure differential! Have you seen a torn O-ring on the power regulator rod? This will happen constantly if you create a pressure differential!

 

[tromic]

I agree with the right sequence.

But I don't understand this sentence:

In the Mirage system, when pre-loading/pre-pumping with the smaller barrel, the power regulator has to be closed, otherwise, you can never build a pressure differential.

In your previous post, it sounded like you said that if I open the power regulator when there's a big pressure differential there can be an "explosion" inside. But with the Mirage system, I think there will always be a big pressure differential when you open the power regulator.
Maybe I misunderstood, the translation is a little bit tricky.

Yo are right David. "But with the Mirage system, I think there will always be a big pressure differential when you open the power regulator." You made tiny modifications, to improve the Mares design...
As I recall you made the power regulator piston larger in diameter. Thats means now you have higher forse to the piston. Maybe the travel of the piston is longer too...? That could couse higher acceleratin and higher kinetic energy... I see it similar to the air gun operation, only the shoting barrel is very short.

 

[Zahar]

P must be equal to P2!

 

[Diving Gecko]

P must be equal to P2!

When opening the power regulator on a Mirage system gun (after pre-loading and final loading), P will be higher than P2. Quite a lot higher sometimes, right @tromic?

 

[Zahar]

When opening the power regulator on a Mirage system gun (after pre-loading and final loading), P will be higher than P2. Quite a lot higher sometimes, right @tromic?

If the power regulator is at maximum then P = P2! Why create an unnecessary difference?

 

[Diving Gecko]

Yo are right David. "But with the Mirage system, I think there will always be a big pressure differential when you open the power regulator." You made tiny modifications, to improve the Mares design...
As I recall you made the power regulator piston larger in diameter. Thats means now you have higher forse to the piston. Maybe the travel of the piston is longer too...? That could couse higher acceleratin and higher kinetic energy... I see it similar to the air gun operation, only the shoting barrel is very short.

Yes, the force on the power regulator when opening is about 1.65 times higher due to the increase in piston diameter. Its travel may be a bit longer, too.
I don't think it's that healthy for the power regulator parts, but my new valve design will hopefully solve that issue.

This was more about how I think there may be a fundamental difference between how the surcompressor guns Zahar is used to work compared to the Mirage system? I am not that familiar with any other type than the Mirage, so I am not sure, though.

 

[Diving Gecko]

If the power regulator is at maximum then P = P2! Why create an unnecessary difference?

The Mirage loading system wont work unless there's a substantial difference. Maybe we are just misunderstanding each other or maybe the surcompressor guns you are describing work differently?

The whole idea behind the Mirage system is that you can put more pressure into the gun than you could load it against if it didn't have the system. E.g. I normally can load a 13mm piston gun at ~22 bar. With a Mirage system I can (theoretically) put 37 bar in the gun and load it with the same effort.

In the Mares Mirage system, you use the smaller barrel to effectively "move the air" from the rear to the front of the bulkhead before each shot. So, you reduce the pressure behind the bulkhead to a degree where the final loading of the shaft in the bigger barrel becomes very, very easy. For example, the Mares manual talks about lowering the pressure in the rear all the way down to 5 bar. And then after you have moved the spearshaft from the smaller loading barrel to the big barrel, you open the power regulator. (And then if you want, you can close it again for a more traditional low power shot).

Are we talking about the same system?

Why create a pressure differential when reloading with a second barrel? This is unnecessary and harmful! Reloading with a second barrel must be done at the maximum power regulator so that there is no pressure differential! Have you seen a torn O-ring on the power regulator rod? This will happen constantly if you create a pressure differential!

Yes, I did break an o-ring in half just a few days ago, that's true. But I am not yet sure if it happened because the edge of the bore was too sharp. I have used original Mirages at ~33 bar of pressure and they work as I described above. And the o-rings on the power regulator of the original Mirage guns don't break or explode when opening the power regulator. At least I have never seen that. I think Pete has used Mirages up to 40 bar and have the memory of an elephant, sorry an engineer not an elephant, and he hasn't described this happening either.

The main issue I think with the original Mirage was keeping the nose cone from leaking. The wall thickness below the loading barrel is very thin and I guess too thin for the non-reinforced nylon(?) they used at the time. So, it tends to crack in that area. Maybe a few other issues, too - but as mentioned I don't think the power regulator was known to fail.
If I recall correctly, Pete puts the death of the Mirage down to being a bit of a tricky gun with not enough upsides compared to the price - they were expensive. Also, the handle was perhaps off putting to some and the Sten/Asso/etc were just cheaper, more reliable and had enough power for most people.

 

[tromic]

You can see what is going on from my sketch of Mirage operatin. There are three positions of power regulator. Full open is max power, midle is choking position for low power and the left is for using the pumping barrel.

 

[Diving Gecko]

You can see what is going on from my sketch of Mirage operatin. There are three positions of power regulator. Full open is max power, midle is choking position for low power and the left is for using the pumping barrel.

Yep, left (loading) is fully closed and would be a Low Power Shot on a regular pneumatic.
I actually think it should be fine to eliminate the choked setting and use the left one as a low power shot after having first equalized the pressure by fully opening the valve. Or maybe even just keep it fully closed.

I did say a few posts above that after a low power shot I wouldn't open the valve back up but just reload like on a classic gun. But it's been +6 years since I hunted with a Mirage system gun and I think this is actually not possible. Because if before the low power shot I had opened the valve, the final pressure just before latching into the sear would still be the max pressure of the whole gun - which I wouldn't be able to load against. Same would go for a throttled/choked shot in an original Mirage - well, actually worse as you are loading against not only the max pressure but also the full volume of air in the gun.

The only way a high pressure Mirage could be loaded like a classic gun would be if the low power shot had been taken with the power regulator (PR) in the closed/left position and the PR had never been opened after the loading procedure. I don't think Mares wanted people to use the gun like that - otherwise why make the choked setting, but maybe with strong enough parts and a redesigned valve it would be possible.
The answer to this may very well be in one of Pete's older posts

[Correction] This is almost too funny. The answer was indeed in Pete's old writings but in a reply to me of all people, 10 years ago where I had found no real world difference between the throttled shot and the full power shot (based on video evidence of mine) and asked him if I could use the closed position as on a Sten and he said, that yes, indeed I could and Mares had even explained this procedure in later versions of the manual. You don't even have to open the valve to equalize the pressure before closing it again. You can keep it shut and decide how powerful your low power shot should be by adjusting how many pre-pumps you do

 

[Zahar]

You load the gun with a harpoon at minimum after a shot at minimum! The piston is already loaded! Further manipulations can be carried out in the maximum position of the power regulator! Load the second barrel and thereby add power to the gun! I have not seen the instructions for using the Mirage gun, but I see from the diagram how to properly work with this gun! The very idea of this gun makes no sense to me! Loading at minimum does not depend on the second barrel if it is not cocked by the piston before firing at minimum! This contradicts the sequence of actions! To increase the power, you need to cock the second piston! Why then switch to minimum? To make loading at minimum easier, you need to move the second piston to the muzzle - gibberish!

 

[Zahar]

You can see what is going on from my sketch of Mirage operatin. There are three positions of power regulator. Full open is max power, midle is choking position for low power and the left is for using the pumping barrel.

I don't see!

 

[Diving Gecko]

You load the gun with a harpoon at minimum after a shot at minimum! The piston is already loaded! Further manipulations can be carried out in the maximum position of the power regulator! Load the second barrel and thereby add power to the gun! I have not seen the instructions for using the Mirage gun, but I see from the diagram how to properly work with this gun! The very idea of this gun makes no sense to me! Loading at minimum does not depend on the second barrel if it is not cocked by the piston before firing at minimum! This contradicts the sequence of actions! To increase the power, you need to cock the second piston! Why then switch to minimum? To make loading at minimum easier, you need to move the second piston to the muzzle - gibberish!

Aha, this explains a lot - we have been talking about different systems all along, haha.
But it's not gibberish Zahar, it's just a different system than what you are used to. But one that has worked in practice for +40 years. Maybe you don't agree with the design but the operation sequences I have described are how the gun was intended to be used by its designers.

Here's an old thread where Ulysses, Pete & Tomi explain the design well, all in the first page:

Mares Mirage

Dear fellow divers/hunters! A couple of months ago I have received a very interesting gift for my birthday: a Mares Mirage pneumatic speargun from a very good friend of mine who is also a spearfishing enthusiast. Externally, the gun is in good shape with only minor scratching on the muzzle.:)...

forums.deeperblue.com

And Tomi's sketch:

Why Did They Fail - Pete Offers An Explanation
Also, it's quite the beloved gun in the Mediterranean but some of the parts let it down and it was too expensive so it went out of production. But as explained, I don't think the valves actually broke. At least I have never seen that I and I have shot two original ones quite a lot.
I found an old post of Pete's where he talks about how the seal on the power regulator (the one sealing against the handle) would leak but not from use:

The "Mirage" was not a popular gun as they were prone to oil leaks, in fact I was talking to the former Mares distributor years later and he said many had come back for repair before they were even sold. The reason they leaked oil (and hence air) is that the "O" ring on the cursor control shaft has a floating metal tube backing, when the gun has high air pressure in it the backing tube is pushed tight on the "O" ring and creates a good seal, but at lower pressure it loses its effect and the guns start to leak. So to pump up a "Mirage" you need to quickly establish pressure in the gun and get that "O" ring seal to close up. That is why I used a portable 12V auto air compressor to quickly push the gun up to 200 psi, then I could take it up further with the hand pump, otherwise I could be in the situation where I was pumping air in and it was leaking out just as fast.

Correction
I have been talking about how Mares had a 5 bar min. limit for the rear chamber. That is wrong, my memory played a trick on me. Their own manual says that 5 pumping strokes will take a 30bar gun down to "0 bar". Apologies.

I am also attaching two Mirage manuals here

 

[tromic]

I don't see!

I know Zahar! Look at the sketch again and read what Davide wrote in his posts about loading Mirage speargun. I can not explain it better...

 

[Zahar]

Any Italian gun with a power regulator has a check valve to bypass pressure from the barrel to the receiver! By increasing the bypass area of this valve, you will have a minimum valve gun with step loading, which significantly simplifies loading the gun! ncreasing the power of the gun with a second barrel requires time and manipulations that the fish will not wait for! If the issue of increasing the power of the gun is the main one, and the ability to load the gun is insufficient, then it makes sense to 1. Increase the bypass section of the check valve and provide step-by-step loading! 2. Pump out the air from the barrel! Everything is transparent and clear! A mirage with two barrels is a mistake of Nature!