A new gun based on the "Mirage" secondary pumping barrel system

[popgun pete]

The Mares "Mirage" has been discussed here over a number of years outlining both its advantages and its flaws. The secondary pumping barrel concept, i.e. load the gun via a smaller ID barrel than the one that shots are produced from could be applied afresh in a new gun that avoids the pitfalls of its predecessor.

The main challenge is after placing the main barrel for best airflow, then the accommodation of the pumping barrel needs to be considered in terms of available space and the method of assembly.

One approach would be to have a concentric barrel gun with an oval tank and the pumping barrel on one side, the only difficulties would be can an oval tank withstand 40 Bar plus service pressure and would the gun be unbalanced to a noticeable degree. Another possibility is a hydroformed tank with a bump for the pumping barrel running along it, but sealing and assembly may prove a problem, so the ideas need to be thrashed out.

 

[popgun pete]

The Mares “Mirage” was designed to be a sleek package where the ingenious internal pumping system was implemented with as few parts as possible, which might sound odd to anyone comparing it with a standard gun. However it could have been made with even more parts if some of the design had not exploited the situation of having a feature do more than one job, such as the airflow into the pumping barrel travelling via a hole using the otherwise “unused” bores created by the mould inserts that minimize the thickness of the plastic sections for faster cool down of the handle component after the moulding cycle in the die ejects the component.

A concentric barrel gun such as the “Sten” allows breather hole access to the barrel from a number of directions, however move the barrel up and the breather hole location becomes limited to the sides and you lose one of those if the power regulator shaft sits on the mid-line. In the “Cyrano Evo” you can see that Mares moved the regulator shaft downwards slightly and changed the power regulator gate shape to provide breather holes on either side of the inner barrel, two on each side judging by the diagrams as I have never pulled one apart. Now a “Mirage” type gun based on the “Evo” (now fitted with a 13mm inner barrel) would be a possibility, but I suspect that the power regulator bulkhead port is in the wrong position as the high inner barrel of the “Evo” was fundamentally to allow that larger diameter transfer port. The pumping barrel will usually be on the gun’s centreline and it has to be clear of the transfer port which does not seem possible, however I do not have sufficient familiarity with the “Evo” to rule it out. Nor do I know if Mares plan a “Sten Evo” using the “Evo” handle. The current Sten 2001 model uses the previous “Cyrano” handle, so it is not without precedent.

Now if the new “Mirage” (maybe it should be called the “Spectre” or the “Apparition”) speargun can locate the pumping barrel close to the tank wall and move the main barrel down then the air breathing access problem into the inner barrel will starts to disappear, especially if the OD of the pumping barrel is reduced as the pumping barrel is not a structural member, whereas the main barrel is. If the partitioning bulkhead stands off from the rear grip section as it does in most other “dual power” partitioning bulkhead guns then the internal plumbing will be easier, but not as compact as it is in the existing “Mirage”. However unless we want to pump the rear of the gun down to zero pressure (gauge) with as few pump strokes as possible we don’t really need the rear chamber of the gun to be so small, so the internal air flow need not be so constricted.

As a gun needs to be assembled quickly and accurately it may be possible to assemble the pumping barrel last of all by inserting it through the front nose cone where it has its own muzzle to trap the pumping piston, but it will then need a means to lock it into the gun as otherwise air pressure getting behind the annular back of the pumping barrel tube would blow it out of the gun. The rubber sleeve blow off valve, basically the pumping barrel’s exit valve, would need to be already inside the gun as it could not be pushed through the nose cone. The problem is any barrel inter-connections need to be completely sealed, something which the current “Mirage” neatly side stepped by making all the moving parts be part of the internal pumping barrel itself and the boss it was pressed onto at the rear.

Something to think about anyway. A “Mirage” with a more concentric main barrel would be less likely to “banana” at the ends, that is the reason for paired “O” rings on the early gun to resist that happening. A lower or concentric main barrel does not need such a raked handle which in the “Mirage” is to set the centre of hand grip pressure up closer to the spear propulsion axis. I never liked that handle as the swinging lever for keeping the gun handle on your foot for loading kept swinging shut at exactly the wrong moment and I was always reaching down to open it again.

 

[popgun pete]

Here is a "Katran", double barrelled pneumatic speargun muzzle, in this case both barrels shoot spears! Must be an act of faith in muzzle loading the second barrel while hoping the first barrel's spear does not blow your head off, however I show it here as an example of a second muzzle projecting from the gun's nose cone. In the new "Mirage" (or "Spectre") this second muzzle would just support the spear for pumping duties and retain the pumping piston inside the pumping barrel, hence the second and lower mounted muzzle would be smaller and much simpler.

 

[Diving Gecko]

I think many people who persist with a Mirage these days can identify areas of improvement. I know I do;-)
I still have a dream to make a CF gun based on the principle but the natural stepping stone would be to use the original handle and bulkhead.
That said, the more I think about it, the less the need for a three stage power regulator, right? I am a bit jet lagged now, but I think a Mirage
Nuovo could just have two positions and a slightly bigger space behind the power regulator bulkhead. So, position 1 would be pre-loading as well as a low power shot and position 2 would be full power. Or am I missing something here? The throttle position 2 is not really doing much for me.
A larger transfer port would help, too.

From time to time, I have been searching for small check valves and over pressure release valves. Would be nice to have some industrial ones that could just screw into a bulkhead of my own design. That said, it's not the hardest thing to make with a lathe and some trial and error later on to find the right spring force.

As I have mentioned elsewhere the 'Mirage Gecko' would not have the pumping barrel go all the way to the front. It would be app. half the length of the gun so as to make the gun substantially smaller in the front part. My long Mirage125 is not as easy to track as I would like and I would not want a longer gun with a traditional 40mm reservoir.

In reg. to the banana'ing, it might present some challenges as in my world, I would push the shooting barrel even higher up and my reservoir would be much in the shape of a C4 gun. I would have to be good with the composites to make up for that inherent assymetric shape.

Also, I would push the handle up so it would sit just underneath the shooting barrel. This means I might have to get clever with the trigger sear and place it on the side with some linkage. Naturally, it would be pushed even further back in the barrel to improve the "band stretch". There are a few different ways to do this.

BTW, your point about the original foot lever swinging open - I will now put that down to your gun being a lemon;-). I have had three Mirages through my hands now, and on none of them this was a real issue. They stayed open nicely. That said, the latest one I was just gifted (and a very early short bulkhead version) might just have that issue, it seemed a bit loosed but haven't had it all put together yet.

So, those were all the thoughts, or most of them. I'd be proud if a proper company snatched them, but they are likely too conservative or stingy to get it to market. Let's see if I get it made myself;-)

 

[tromic]

From the sketch on https://forums.deeperblue.com/threa...es-mirage-in-photos.106918/page-2#post-960683 it is visibabe that you can have only two position power regulator. But would be it good a solution?

 

[popgun pete]

The whole point of this thread is a totally new gun without the "Mirage" handle as that is the existing gun's main problem. Forget the existing gun as some sort of icon eagerly sought by collectors, in fact a lot of collectors just have their guns hanging on the wall as something to brag about and treat them like trading cards or stamps, so they do not really care about how the gun functions. The swinging lever not staying open on my gun is not due it being a "lemon", it is just that the lever has no bump on the top to flip it open from the top near the pivot pin and once inside the recess the lever tends to stick in position (when closed), otherwise it swings around too freely. Readjusting the gun handle to sit on your foot when there is a lot of surface movement pushing you around makes keeping the grip handle lever open difficult, as I don't often dive in a "mill pond" with flat conditions.

The other aspect of a "Mirage" is its weight, the 80 cm model floats butt up, muzzle down in the water column. However flood the butt and it floats muzzle up, but only just as it is then on the verge of being a sinker and will be drifting below the surface. That the gun is a floater is due to the design keeping the weight down despite the extra barrel and valves, so any new gun needs to be as economical in terms of the weight of the parts. Some weight saving could be found in the use of a carbon fibre tank, but I would not be that comfortable with a gun using 40 Bar plus unless such a tank had been well and truly tested, and that includes testing to destruction. Any new gun will need to be as smart design-wise as the original was, but by opening the interior up and stretching it out at the rear end it should perform better. I am thinking here of a mass production gun which Mares could make, maybe using parts of the "Evo" as seen in the cylindrical tank version, but with the sear lever on the level rather than sitting at an angle as it seems to be now. In the attached diagram I have manipulated the sear lever to reflect this. My ownership of a "Mirage" is totally irrelevant to what I am trying to get across here, in fact I just see the "Mirage" as a design guide of what can be done with a few simple shapes and how it can be improved by varying some of the parts and how they are assembled. My guess is when the "Mirage" was designed they styled the gun's exterior first and then fitted the necessary parts inside the "envelope", which meant squeezing up the interior which produced the long rectangular duct and the dog legs in the airflow path from the transfer port into the rear of the inner barrel.

 

[Diving Gecko]

I think a two-stage solution is totally fine. Thing is, my throttle function on position 2 doesn't work well anyways and I don't ever use it.
I would have to do some proper testing to see if the throttle function can be made to work but on the other hand, for a 130-140 Mirage I don't think I would have much need for a low power shot anyways.
And if I did, I think a bigger reservoir for position 1 would be fine.

 

[Diving Gecko]

I agree, that for this thought experiment it is a good idea to start with a cleaner slate.
As for the trigger sear, ideally I would even have a pump fill port somewhere else so I could just use a short bolt to hold the barrel in the handle. Also, the sear itself could be half the length as the rear part, after the pivot point, could be bent 90%. That would buy, perhaps, 5cm of extra effective barrel length.

BTW Pete, I don't mind repeating myself as you know I have a ton of respect for you.
People will end up reading this thread as much for knowledge on old Mirages as for ideas for this mirage of a Mirage that we are entertaining here.
I have had three Mirage handles with no issue with the lever and one possible one;-). I don't mind standing corrected if more people chip in and say theirs is too loose but no need to make it gospel just yet that Mirages have this issue. All in respect, as always

 

[popgun pete]

The point I was making is that if you don’t have a raked handle then you don’t need the swinging lever to keep the back of the handle against your foot during muzzle loading. You know this with your own guns, so any new “Mirage” should just stick to a simple handle. For a period in speargun design there was a thought to maybe moving to more raked or highly angled grip handles, a good example was the Sampson band gun. It was not called the wrist breaker for nothing!


Earlier in the “Mirage Gun” thread I remember the two versus three position gate was discussed. My view is that you don’t need three positions or even “low power” on a 40 Bar gun, but you do need the transfer port well plugged for the pumping barrel operation. I would have the same length travel in the gate for the selector knob, but no position 2 as there is in the current gun.

Design-wise, and from the two metal sleeves used in the original power regulator shaft tunnel, my belief is that Mares originally intended for the brass piston plug to retract further back in the grip handle and back away from the airflow path, but the gate travel would need to be about twice as long as it is now, so they did not do it.

 

[popgun pete]

The gate travel "as is" would be OK for a nearly fully retracting brass piston plug if the plug only had to enter the transfer port and seal it off and not move any further forwards inside it. Then the "Mirage" would be "load" with the pumping barrel (selector at 1 and down in the dog leg of the gate) and "shoot" at full power (selector at 3, which would be renamed 2, fully back in the gate). If you look at the simple rear face of the original bulkhead this may have been how the "Mirage" had at the prototype stage been intended to operate, only the marketing department said otherwise. Unlike their other guns shooting with the selector down in the gate at position 1, the "Mirage" cannot use the volume in the pumping barrel due to the non-return valve located at the pumping barrel inlet, so the "Mirage" then shoots with the pre-chamber volume which is tiny. Yet during loading of the gun the "pre-chamber" is effectively the volume of the pre-chamber and the pumping barrel combined. If you do the maths on the "Mirage" then you can understand how it works by shifting gas molecules, but a different number of molecules for each stroke of the pumping barrel as while the pumping barrel delivers the same swept volume, the pressure in the pumping barrel changes each time it refills from the back end and the inner barrel volume of the gun (the pressure gets progressively lower each time as can be seen in the table shown at figure 3).

 

[popgun pete]

I have been studying the "Cyrano Evo" innards on the Mares video and believe that it could be used for a new "Mirage" type gun. You would throw away the "Evo" regulator block and replace it with one similar to the "Mirage", but it would need to index on the forward projecting flange on the "Evo" grip handle. The "Evo" has a power regulator rod controlling a transfer port plug and one-way valve combined, so that would need to be factored into the new design. The rear grip handle is quite roomy inside as we can see from this view.

Here is the power regulator plug and one-way valve with its biasing spring.

 

[popgun pete]

Here is the tilted sear lever which can barely hang onto the piston's mushroom tail.

and the rounded periphery of the mushroom head that makes its "escape" easier.

 

[Diving Gecko]

The Evo HF handle has a bigger seal on the power regulator, too. It is 8 or 9mm vs. the traditional 6mm.

 

[popgun pete]

The Evo HF handle has a bigger seal on the power regulator, too. It is 8 or 9mm vs. the traditional 6mm.

In order to make a space for the pumping barrel that plug may have to be reduced in size, in other words use only the power selector shaft of the "Evo" and return to the standard transfer port plug size. That would mean using a separate non-return valve as employed in most other Mares guns, including the "Mirage", and probably dumping the over-pressure valve which has a heavier coil spring. I don't know if that valve ever opened in my gun, it is there to place a limit on the maximum pressure differential that can occur in the gun.

I had been waiting for someone to open up an "Evo", but failing that I looked at the Mares 3D modelling video to see which parts go where. If a donor gun was needed then I think the cylindrical tank version of the "Evo" is the way to go as you need that offset full diameter front bulkhead found on say the 70 cm model. (i.e. to use it as a pattern template)

 

[popgun pete]

Why we want the "Cyrano Evo" is the raised inner barrel can breathe through 4 portholes, two on each side, that have airflow access in the more open interior of that gun's rear handle, much better than the rectangular channel or duct used in the "Mirage".

The non-return valve may be here, but it is not discussed in the video.

 

[popgun pete]

An approximation of the proposed "Mirage Evo" is shown here.

 

[popgun pete]

A direct comparison is shown here.

 

[popgun pete]

The so-called “variator” in the “Cyrano Evo” was a bit of a mystery until I drew this diagram. How it works is the stoke of the variator, which is the actual transfer port plug, is less than the travel length available in the control rod selector gate between high power and low power positions. Hence the variator can move (against the coil biasing spring) on the control rod by the length of the green line, which means that when the pressure in the front tank goes up the variator plug cannot move back far enough for its “O” ring to exit that bore of 9 mm ID, hence the front section remains sealed off. However when the control rod moves back to the high power position then the variator can move back even further and uncovers the larger opening marked with an “X” (refer to the inset diagram).

 

[popgun pete]

Integrating the variator into a "Mirage" has a few problems, the main one being that a 9 mm diameter transfer port bore for it to run back and forth in would almost touch the periphery of the larger tubing required for a 13 mm ID inner barrel, there may be a half millimetre clearance at best. The "Mirage", as with all the "Sten" family of rear handle pneumatic guns, has a 7 mm OD transfer port plug, or brass piston, on the end of the power selector rod control shaft. Expanding that size out to 9 mm with the matching transfer port in the partitioning bulkhead gobbles up any existing space left between them. A secondary consideration is that with a 65% increase in frontal area the transfer port plug, and the control shaft resisting it from moving, would have to face the operating conditions in a "Mirage" where 40 Bar plus is on one side and near zero pressure is on the other. That may be a step too far for the main tank, or main reservoir isolation system that the "Mirage" relies on for its loading via the secondary small bore pumping barrel which will be pushing most of the gas in the "Mirage" into the front (main) tank.

When Mares announced the "Cyrano Evo" they stated that it had a larger transfer port, but strictly speaking it does not. In order to stop the variator falling off the control shaft and dropping into the front tank, as unlike the brass piston plug it is not directly threaded onto the power selector rod control shaft, they made the opening in the bulkhead only 6 mm in diameter in order to keep the variator "captive", whereas it is a 7 mm diameter transfer port in all their other "Sten" family of guns. The advantage of the variator is that as it backs away from the 6 mm diameter opening, or transfer port in the partitioning bulkhead, it then opens up to be a 9 mm diameter port. Thus gas rushing from the front tank during the shot first passes through the 6 mm diameter port which widens out to a 9 mm port and this must improve the airflow (as otherwise why do it that way?). Marketing considerations come to mind as a possible answer!

Because a "Mirage Evo" would draw on 40 Bar plus shooting pressure (after cocking of the gun) it could probably get by with a 7 mm diameter transfer port as before, especially if it is a dual power gun, either full power using all the gas stored in the gun expanding for the shot or a weak shot with the inner barrel and pre-chamber volumes only contributing gas.

 

[popgun pete]

On reflection I think the "variator" is a gimmick that does not add anything to performance. For it to be effective the coil spring behind the plug section at the front end would need to be strong in the low power LP position and weak in the high power HP position. Unfortunately you cannot have it both ways! The reasoning is that in the LP position as soon as pressure in the front tank is higher than in the rest of the gun the plug section will be pushed back to the position shown with a bold outline once the pressure differential can collapse the coil spring. That is the same position that the threaded control rod attachment brass piston plug would occupy. In the HP position the sliding plug section will be pushed back on the coil spring by the airflow during the shot, and as that air flow slows down then the plug section will move forwards to the light outline position in the above diagram which would throttle the flow. By that stage the shot will have been nearly completed, hence the throttling will have little impact. Yet a threaded control rod attachment brass piston plug will act in the positions shown by the bold outlines on the diagram, so what advantage does the sliding "variator" plug section offer? None in my opinion as the 6 mm port opening with the floating attachment "variator" plug will be less effective than the usual 7 mm port opening in the front face of the partitioning bulkhead with a threaded attachment plug.