Mares Mirage

[popgun pete]

Here is the original instruction manual for the "Mirage". I have reduced the pages by 50% in order to reduce the size of the files, but they should still be readable. The document folds in two places to form three panels, thus there is an "A" side and a "B" side printed back to back. The lower right corner was torn off the cover page, but I have restored it using the duplicate material in later publications where diagrams show how to load the gun off the foot or the thigh on the reverse side of that page. I don't remember anything printed in the missing corner of the front page, so it is shown as blank.

Now replaced with Acrobat versions which will stand magnification better than the jpeg files that I have now removed, but which still show the same material.

 

[popgun pete]

Note that while the original "Mirage" instructions fully describe the operation of the pumping barrel system with the power regulator selector set at position #1, they don't say anything at all about the power of the shots available at selector positions #2 and #3. It was obvious that the rearmost selector position #3 would provide maximum power as that is also what it does on a "Sten", therefore position #2 had to be for a "low power" shot, but how low and was it conserving of loading effort as it is on a "Sten" (or a "Cyrano" which was then years away)? That means if you take a low power shot then you only have to reload for the energy used in that shot, the remainder of the energy stored when using the pumping barrel system will still be available provided you don't change the power regulator setting after the shot. Hence you should be able to muzzle load the gun via the main barrel rather than use the pumping barrel as the pressure behind the main barrel piston will now be lower. I soon found out that did not happen in selector position #2 and put that down to the transfer port not sealing properly unless the regulator lever was at selector position #1. I never thought about selector position #2 possibly being a throttled shot which used up all the pressure differential created in the gun by your loading effort, but in hindsight the original instructions don't mention direct muzzle loading and seem to consider that you will use the pumping barrel after every shot, which makes sense if you expend all the air pressure differential stored in a gun which is charged to around 40 bar.

The later instruction manuals, which I had never seen before reading them here, appear to be written from an entirely new perspective where the function and operation of the "Mirage" gun is completely reappraised, especially as the throttling effect had since been modified (reduced) in selector position #2 in order to provide more power for that shot by adding a side window to the rear edge of the transfer port in the redesigned partitioning bulkhead. In which case there should now be an appreciable difference between shots taken at selector position #2 and selector position #1, but is there? Mares evidently thought the change was needed as otherwise they would never have made it.

I would have liked to see the "Mirage" produced without the angled rear handgrip (I did not like the folding lever which sometimes swung shut just when you needed it to stay open for loading the gun off your foot), have only two power regulator selector positions (i.e. no throttled shot which wastes some of your previous loading effort) and a larger pre-chamber for a more powerful "low power" shot. If the pre-chamber is too small then the air allowed to expand for that shot moves from a very small volume (the pre-chamber) to a much larger one (i.e. the inner barrel volume plus the pre-chamber volume) and that causes too large a pressure drop in the inner barrel which reduces the power of the shot, although it makes the gun much easier to reload via the main barrel. The downside of a larger pre-chamber is that you have to shorten the length of the pumping barrel and my thoughts are that when the "Mirage" was first designed in the early seventies they wanted to make the small diameter pumping barrel as long as possible with a short piston that maximized the operating stroke of the pumping barrel. This allowed the number of pumping barrel strokes to be kept to a maximum of five strokes in the original gun, a shorter pumping barrel would have required more pumping barrel strokes to achieve the same result.

 

[Diving Gecko]

Quick question and I'm sure it is between the lines here, but my brain is a bit fried from the tropical sun today:
Say you have a fully loaded (throttling model) Mirage which has had the power selector at pos. 2 or 3. Would it not be OK to move to pos. 1 for a low power shot as on a regular Sten?
Am I missing anything?

As a side note and to partly answer a question posed by Pete above, I, personally, feel the difference between power on pos. 2 and pos. 3 is too little. So little that I actually can't tell the difference. So, I would suspect that on my gun at least, the difference between 1 and 2 would be substantial.
I will look into a slight modification when I take it apart next time: I will add a spacer on the power regulator rod where the knob screws into the straight part of the rod. This will push the regulator further into the bulkhead at all positions but should make the throttling action more pronounced on pos. 2.
I have already checked that on position 1. the regulator does not protrude so far forward as to not seal.

 

[Diving Gecko]

To add to my observation about the lack of difference between shots on pos. 2 vs. pos. 3.
This is what I base it on.
I took some shots on water bottle targets today and saw no difference in how the shots were placed (all a bit too high, as a rule) whether I shot on 2 or 3.
Then, a tad more scientific, I reviewed the footage. It was shot at 100 frames per second. I counted how long it took to fully stretch 4 full loops of shooting line from the time the spear started to move.
It took 35-37 frames for each shot. Maybe on average two frames more for shots on pos. 2. (No matter what, it's only a tad more than 1/3 of a second to shoot 8 lenghts of mono...!)
So, if we can say that velocity is a usable measurement for the power of the shot, then I have no practical difference at all between the two power modes.

 

[popgun pete]

Quick question and I'm sure it is between the lines here, but my brain is a bit fried from the tropical sun today:
Say you have a fully loaded (throttling model) Mirage which has had the power selector at pos. 2 or 3. Would it not be OK to move to pos. 1 for a low power shot as on a regular Sten?

Yes, that is right, in fact the later revised instructions say that you can do that or use one or two pumping barrel strokes to drop the pressure for even lower "low power" shots, provided you leave the power regulator selector in the #1 loading position after performing those strokes and for when you take the shot.

I used my "Mirage" like that a few times, i.e. put the selector knob in position #1, conduct the 5 pumping barrel strokes, load the spear in the main barrel with next to zero effort, flip the selector knob up which sends it straight back to position #3 and equalizes pressure throughout the gun and then push the selector knob forwards and down to position #1 for the actual shot. That gives you a "low power" shot in the same sense as the "Sten" does using only the compressed air from behind the partitioning bulkhead. You can reload after that shot via the main barrel, although the final push to latch is still against the gun's cocked to shoot pressure as the pressure in the inner barrel once more attains the same pressure as everywhere else inside the gun.

At lower initial gun pressure you can forgo using the pumping barrel and just use the gun like you would a "Sten", ignoring position #2 completely.

 

[popgun pete]

As a side note and to partly answer a question posed by Pete above, I, personally, feel the difference between power on pos. 2 and pos. 3 is too little. So little that I actually can't tell the difference. So, I would suspect that on my gun at least, the difference between 1 and 2 would be substantial.
I will look into a slight modification when I take it apart next time: I will add a spacer on the power regulator rod where the knob screws into the straight part of the rod. This will push the regulator further into the bulkhead at all positions but should make the throttling action more pronounced on pos. 2.
I have already checked that on position 1. the regulator does not protrude so far forward as to not seal.

If positions #2 and #3 shoot the same in the revised "Mirage" gun then it must be down to the throttling effect not being great enough, which seems surprising given that Mares made the change. Something one needs to be aware of when reassembling the gun is that the regulator shaft screws onto the selector knob and you can unintentionally vary the length of the shaft so that the power regulator piston's plug stops in slightly different positions in the bulkhead. I only noticed this when I could see the selector knob sitting in slightly different positions with respect to the rear of the gate in position #3 after I had "fixed" the gun each time and it was once more under pressure. When I purchased the gun I could see a gap indicating that the connecting thread was not fully screwed up, but I never checked the number of turns required to get it back to that same spot.

 

[Diving Gecko]

If positions #2 and #3 shoot the same in the revised "Mirage" gun then it must be down to the throttling effect not being great enough, which seems surprising given that Mares made the change. Something one needs to be aware of when reassembling the gun is that the regulator shaft screws onto the selector knob and you can unintentionally vary the length of the shaft so that the power regulator piston's plug stops in slightly different positions in the bulkhead. I only noticed this when I could see the selector knob sitting in slightly different positions with respect to the rear of the gate in position #3 after I had "fixed" the gun each time and it was once more under pressure. When I purchased the gun I could see a gap indicating that the connecting thread was not fully screwed up, but I never checked the number of turns required to get it back to that same spot.

Honestly, I do not know how surprising it is that the throttling is not spot on - unless you make the assumption that the engineers had better time and resources back then than now. Not to be spiteful, but it seems the newish Evo HF has some teething problems as well. But Mares are not the only ones as Sporasub have quietly upgraded a few parts in the One Air since launching it. I am sure the list is longer. Of course it is disappointing when companies rush products to the market but I am not sure it was much better 25 years ago. (You even mentioned 1st version Mirages leaking before they were even sold to customers).
All these issues, then and now, seem to me to have been perfectly identifiable with enough of a proper, real-world test period. I am sad to say it sometimes look like the testing period lasts only long enough for pics to be made for the upcoming catalogue for the manufacturers.

As I mentioned above, I hope there is a remedy for this by indeed adjusting how far into the bulkhead the power regulator piston is allowed at each position by adjusting how far into the rod, I screw the knob. I assumed that fully-in would be the default but maybe, as you saw on yours, there is supposed to be a gap. If so, then it could give an increased throttling effect but still not 100% great engineering;-)

That said, I do love owning, shooting and catching fish on what could be the most advanced (non-hydro) pneumatic speargun produced and if it worked flawlessly I would not have so much to tinker with;-)

 

[popgun pete]

Advanced technology has certainly accelerated the ability to create new designs and evaluate how they will be constructed before any components are actually made as it can all be done in 3D in the computer. Unfortunately these computer simulations don't guarantee that everything is going to work flawlessly or will be durable in the real world, but the capacity to make changes in shorter time spans is greater now as computer controlled machinery creates the complex injection moulding dies. That may have made the manufacturers more adventurous than they were in the past when there were no computers and it would all be "hands on" work with physical models and long-term employees using their accumulated experience, something that may be missing today, before they committed to the considerable time and expense in creating the moulds by transferring the design directly from the physical models. Problems with guns in the past seemed to be more assembly related rather than design problems as a longer development period had previously ironed out most of the bugs. Now with the increased demand for new models in ever shorter time frames the designs appear to be "less sorted" than they were before, hence what in a sense are "Beta" versions go to the "early adopter" customers.

I am sure the workers on the "Mirage" production line had all the information on the required adjustments, it was just a case of whether they had the time to assemble them properly and except for the guns holding pressure (maybe only checked for a minute or so) the guns were possibly shipped out without any further checking. I never shot my gun in original "ex-factory" condition, I had to stop it leaking first, so the performance in position #2 may have been affected by that power regulator shaft adjustment as I never paid much attention to it (when it now looks like I should have, but I failed to notice that there was a diameter change inside the transfer port bore) other than to replicate a gap of some sort which you could see by looking down into the selector gate. If you can get the "O" ring on the brass piston to sit slightly rearwards of the step in diameter before it actually plugs the transfer port then that should increase the throttling effect in position #2, provided that in position #1 the "O" ring stays inside the transfer port and does not pass right through it. Maybe in my earlier "Mirage" gun I have had the brass piston too far forwards as the selector knob elbow nearly hits the rear of the gate in position #3, I actually adjusted it to leave a tiny gap there which means a larger gap where the threaded sections of the shaft join.

 

[popgun pete]

The difference in barrel/piston cross-sectional areas facing the compressed air pressure inside the "Mirage" gun (13 mm for shooting, 10 mm for muzzle loading) provides a reduction in muzzle loading effort in terms of the force required to move the small piston compared to the larger one. This reduction is derived from the ratio of the barrel cross-sectional areas which can be simplified to the ratio of the inner barrel diameters squared (as pi and dividing by 2 for the radius cancel out top and bottom in the fraction), i.e. 100/169 or 0.59, therefore you only have to supply 59% of the force that you would have applied when muzzle loading using the main barrel. However more barrel strokes are required in that 10 mm barrel in order to move the same mass of air molecules inside the gun (or the same air volume at cocked gun pressure) as if you were loading the gun via the 13 mm main barrel. At 40 kg/sq.cm. initial charge pressure that represents a force of 31.4 kgf compared to 53.1 kgf (69 pounds and 117 pounds respectively)!

You do not save any energy using the pumping barrel system, in fact you probably use more with the extra friction involved (6 barrel strokes, 5 in the pumping barrel and 1 in the main barrel versus only 1 using the main barrel), but that does not take into account the energy lost with failed latching attempts when you pushed the shaft in so far and then it came out again without latching, or the piston scarcely moved back at all in the main barrel with the spear shaft flexing under the strain instead while you nearly bit through the lugs in your snorkel mouthpiece!

Why does it take five pumping barrel strokes to achieve the same result? Well flipping the power selector knob or cursor up from position #1 causes the pumping barrel to refill with pressurized air as well as the pre-chamber. Note that the pumping barrel has a different length and compression ratio compared to the main barrel as while the main barrel pumps to the entire gun internal volume the pumping barrel only pumps to the front tank surrounding the two barrels. Basically the two barrels, acting as pumps, have to move the gun to the same "cocked to shoot" pressure, but before restoring the gun interior to that same pressure level the pumping barrel has to move the front tank to a higher than "cocked to shoot" pressure and that requires more pumping barrel strokes. To keep that number of strokes to a minimum the "Mirage" has a smaller pre-chamber than say a "Sten" because less pressure build-up is thrown away when the front tank drops in pressure to refill the rest of the gun with the main piston latched on the sear lever.

The revised instruction manual's lower than "low power" shots with the power selector knob remaining at position #1 and using one or two pumping barrel strokes before loading the spear in the main barrel against the intermediate pressures achieved during that staged loading process are somewhat academic as any time you have the main piston latched you might as well flip the selector knob up from position #1 and have "full power" with the option of going back to "low power" by returning the selector knob to position #1 before any shot is taken. Although you will have isolated the front tank and pumping barrel volumes by doing so, the "low power" shot uses the gun at the "cocked to shoot" pressure and not some lower intermediate pressure raised by the act of loading in the main barrel.

 

[Diving Gecko]

Thanks so much for the write-up, Pete.
It's welcome timing as over the last few days, I have really started thinking a lot about how to modify my Mirage (and hopefully an upcoming one) even further.
For the next one, there is a chance that I will make it longer than the original 100/104 model which means, I would need a new shooting barrel, pumping barrel and outer tank.
The reason for wanting a longer gun is that I would love to simplify my travel set-up and just travel with two guns which share the same parts. Also, I don't dive/spear enough to develop an instinctive connection to different guns and I realized on my latest trip that changing back and forth between my Mirage and One Air did mess a little with my targeting skills. Diving with two "identical" guns of different lengths could help with that.

While the outer tank will definitely be from carbon fiber, the shooting barrel could be an original Mares from a 120 Sten (or a custom made one) but obviously, the pumping barrel would need to be custom made. And this is where I am considering yet another modification and taking it down from an ID of 10mm to 9mm to aid me in loading at higher pressure than I do now.
I know this will mean that running an 8mm shaft with slider wont be possible but I might still go for this. The reason is that my current Mirage at 30 bar is almost on the limit of what I can load with a 7mm shaft.
With a modification like this, I would also need to do more pre-strokes than the normal five but I don't think that's an issue at all. The difference in time-to-load between five and six or seven strokes is negligible.
Do you see any mechanical reason, I could not go forward with this modification?

One thing to consider though which might speak against the need for this mod on a longer gun: I find that on my longer 11mm barrel gun with comparably the same or higher pressure than my shorter 13mm gun, the longer gun is easier to load. Eg. my One Air 120 (11mm barrel) is easier for me to load at 29bar than my Seac 90 (13mm) at 18-19 bar.
I can think of a small handful of reasons for this (in an attempted order of importance):

• The long gun rests on my foot with my legs fully stretched and I don't have to lift up my leg to aid in loading. I do with the smaller gun
• On the long gun, I use an extended loader which lends more support to the spear during loading
• The but of the One Air (longer gun) handle never really slips while the modified handle on my shorter gun has a tendency to do so
  
• The long gun has a 7mm spear and the shorter one a 6.75mm, not much difference but might help a little on loading the long gun

So, excuse me while I try to do a little math to figure out, what I theoretically could load a 120 Mirage at - based on being able to comfortably load my One Air 120.
I can load my One Air 120 (11mm barrel) at 29bar. If I am not mistaken, the difference in area and force needed between an 11mm piston and 10mm is app. 21%, so if my math holds up, this says I should be able to load a long Mirage at 35bar?

 

[popgun pete]

You can lengthen the gun with longer barrels and tank all extended by the same amount provided that you can source the longer tubing and in the case of the barrels have them machined for the necessary features such as grooves and slots, but that will involve someone working from the original items for the necessary dimensions or having them properly documented on an engineering drawing. It is not an insurmountable task, but the parts need to be made with precision to obtain the correct lengths so that the muzzle nose cone and partitioning bulkhead trap the pumping barrel between them and seal at both ends.

A 9 mm ID pumping barrel will further improve the loading effort reduction (81/169 or 0.48) with respect to the main 13 mm barrel loading, however the rear end of the pumping barrel still has to fit the boss on the partitioning bulkhead which is sized for 10 mm ID tubing. Using a 9 mm pumping barrel would probably rule out 8 mm diameter spears as 0.5 mm is a small side clearance in a barrel of that diameter even with bare tail spears. Hydropneumatic guns use those size combinations, but they have stainless steel barrels that are more resistant to the shaft bowing and touching the wall of the barrel than is the case with alloy barrels. As an 8 mm shaft retains its velocity better at long range I suggest you keep that option open and remain with the 10 mm ID pumping barrel which also means you can use the existing piston.

As for your last question your calculation is correct, if you can load the "One Air" then you should be OK with the "Mirage" with the 10 mm pumping barrel given that the ratio of 35 bar to 29 bar is 1.207 and the ratio of the respective barrels is 1.21.

 

[Diving Gecko]

Hey Pete,
Just wanted to share pics of how the power regulator setup looks in my, later version, Mirage.

Behind the brass bushing (L-R) you will see: metal washer, red plastic bushing (inserts into the handle), o-ring (quite squared and should be changed) and finally a hard rubber o-ring-backing washer

 

[popgun pete]

In my gun the brass piston only has two flats instead of a hex nut on its rear end, then there is a long tubular metal spacer of chromed brass, an "O" ring and then another metal tube of a slightly different size which is a tight fit in the selector shaft tunnel in the rear plastic handle. Trapped in place behind that second tube is another "O" ring of the same size as the first. The last two items on the shaft were hidden (they are not shown on the parts diagram) and were only revealed by making a tiny hook to catch inside the back edge of the rear metal tube and then pulling it out of the handle. Why I had to do that was as originally assembled there were two "O" rings found side by side at the rear of this "buried" second tube and none present at all between the two metal tubes! Thus the gun had been wrongly assembled at the factory. The rearmost "O" ring must act as a gasket to seal the rear tube in the handle (if it is even intended to be there, I never tried leaving it out), while the front "O" ring located between the two metal tubes is the dynamic seal for the shaft. Pressure in the gun stops it moving back and forth as nothing traps that "O" ring in the handle unless the regulator shaft is fully back in position #3 which causes the brass piston to lean on the front tube which in turn squeezes the "O" ring against the exposed inner face of the second tube. If that does not happen then the gun leaks both pressurized air and oil through the regulator shaft tunnel, hence all those early "Mirage" guns covered in oil in the shops. There is a clue in the instructions, but few would have understood its true significance and that included me until I saw how the gun was constructed inside. Unless you pulled the selector knob back to slide the dynamic seal "O" ring rearwards along the shaft so that it sat firmly against the exposed inner face of the second metal tube you could be losing air as fast as you pumped it in with the hand pump. Only when you managed to develop some pressure in the gun would the "O" ring remain in the position necessary for sealing, but without knowing that fact the "Mirage" was viewed as an unreliable gun which tended to leak, especially if you had pushed the selector knob forwards with the gun depressurized and unwittingly moved the "O" ring forwards and off its seat. This is probably the reason for the redesign of the power regulator in the subsequent models. Note the absence of a biasing spring on the power regulator shaft compared to those found in other Mares guns which holds the regulator shaft "O" ring in the correct seating position.

From the front face of the brass piston to the rear of the stainless steel regulator shaft with the selector knob removed the overall length of the shaft assembly is 8.8 cm. which looks to be shorter than the shaft assembly is in your later gun.

 

[popgun pete]

I should point out that the small gap at the shaft join where the selector knob's threaded front end screws into the rear of the power regulator shaft always passes through that rearmost "O" ring position whenever you push the selector knob forwards in the selector gate. That causes the rear "seal" to leak, which is why the second "O" ring is positioned further forwards in the power regulator shaft tunnel in order to prevent that from happening. Possibly that rear "O" ring is a consequence of making the larger inner bore of the tunnel longer than it really needed to be and the second metal tube is to effectively shorten it again, but why make it longer in the first place? Possibly the tunnel was going to accommodate a longer assembly that had a biasing spring, but Mares decided to use a simpler design that required less space. Note that in the "Mirage" the power regulator piston had to retract back inside the handle for the piston's front face to be slightly recessed from the front of the handle. Otherwise with a flat partitioning bulkhead sitting directly in front of the rear handle the "Mirage" was not going to be able to breathe very well. In a "Sten" and a "Cyrano" the brass piston has the cylindrical pre-chamber to retract back into, therefore air can flow past the piston to access the inner barrel interior from a number of directions inside the rear handle, but the "Mirage" used to be more restricted as the air had to flow through channels inside the rear handle with the piston sitting in the front of the open-sided channel on the left hand side blocking most of it off.

When redesigning the "Mirage" they have given it a small cylindrical pre-chamber for the retracted brass piston to sit inside as I am sure the brass piston no longer retracts right back inside the frame of the handle. This modification would improve the air flow past the piston even though the interior of the handle itself may be unchanged.

 

[popgun pete]

Now I understand the reason for changing the "Mirage" bulkhead and handle. The open-sided channel on the left hand side has been eliminated from the front of the handle in the revised version of the gun. This channel used to create a short, curved, transverse pathway to connect the rear of the transfer port to the rectangular airflow channel in the handle that runs rearwards underneath the main barrel. That curved pathway was necessary as the bulkhead originally had a flat rear face in order to minimize the volume of the pre-chamber. When the gun fired the air had to perform two right-angled turns before reaching the air breathing slot in the inner barrel, whereas after the change the air approaches the rectangular channel from its now open front end as the transfer port is located in a small well positioned in front of the channel instead of being off to one side of the channel. I say "rectangular", but the roof and floor are curved as the "roof" is the wall of the main barrel, however I will use that term to describe the channel. Thus the modifications are about improving the "full power" shot by straightening out the airflow path in the "Mirage" after it passes through the transfer port. This was needed as the "Mirage" had a somewhat less than expected "full power" shot even at 40 kg/sq. cm. or 40 bar in its original form. The problem with the "Mirage" is that the rectangular channel under the main barrel limits the airflow to the inner barrel, it is basically a long throttle. There is no getting rid of it as its floor helps brace the area that supports the seating bush for the pumping barrel inlet valve, there is a small hole in that floor at the front end which allows air to access the blind-ended tubular channel below the floor that feeds air into the pumping barrel. I expect that the small hole is drilled as there would be no simple way to mould it.

I would say the limitations on the airflow capabilities inside the rear handle are what killed off the "Mirage" as it may be easily loaded at high pressure, but the gun does not do enough with that pressure. The channels that provide the necessary plumbing and separation of airflows and the desire to minimize the pre-chamber volume in the rear handle work against the gun's efficiency. The throttled selector position #2 has not much effect in a gun that is already throttled by small cross-section channels or openings. Contrast this with the more open interiors of later rear handles for pneumatic spearguns that help to improve internal airflow to the inner barrel.

 

[Diving Gecko]

Hello Pete,
Here is a pic of my handle. The square'ish channel might be slightly bigger in the newer handles(?).

I have an idea for a modification and I am aware that structurally, I need to be careful but I would like to hear your input on the functionality of such a modification.
In either the hole where I inserted the pencil or the hole just beneath it, I could drill a hole exiting in the square tunnel. Or remove some of the plastic at the front of the handle between the hole and the tunnel to aid in the transfer of air during a full power shot.

Here is a picture trying to illustrate where material would be removed (either one of the red areas). Also, there is empty space in the power regulator bulkhead just in front of both of these holes, so airflow on that side is not restricted:

Besides the structural considerations, did I miss anything that will jeopardize functionality?

 

[popgun pete]

The "rectangular" channel looks the same size as the one in my handle, so the mould modification is confined to the power regulator section which has eliminated the cutaway on the left hand side by replacing it with the mounting hole for the red plastic plug that retains the dynamic seal "O" ring in the power regulator shaft tunnel. I notice the "buried" rear metal tube that previously formed that "O" ring's seat has been replaced by a step in the plastic tunnel bore (which is what it should have been in the first place, only Mares moved the seat forwards in the handle and that required the insertion of the metal tube). I think if anything was going to make a difference to the breathing then Mares would have done it themselves when they modified the handle as they had to machine the injection moulding die, including the metal inserts that withdraw when the die is opened. Those inserts create the voids and holes, otherwise the product could never be removed from the die once the plastic cooled. The blind holes are to reduce weight and the thickness of plastic sections so the parts cool without shrinkage that causes sinks in overly thick plastic sections. You often see these holes in plastic mouldings that seem to have no purpose, but that is what they are for.

The holes on the right hand side that you have indicated could be broken through into the rectangular channel by drilling the intervening plastic webs out, the upper of the two holes runs back for 8 cm and the lower hole for 5 cm, which would indicate the upper hole is the most likely candidate, however that may adversely affect the plastic handle's support of the inner barrel tube in the handle moulding. If you look at the rear of the inner barrel tube then you will see the sear lever slot, it is cut wider at the back end of the tube behind the sear lever pivot pin. That opening is how the inner barrel breathes as there are no other holes penetrating the inner barrel tube, unlike the other Mares pneumatic guns which have a breather hole on top. As the "Mirage" inner barrel is raised up in the gun and is not concentric with the tank then there would be no access to an upper hole in any case, but possibly one could be added on the right hand side provided it sits behind the piston seal with the gun cocked. Measuring 8 cm back from the front boss of the handle frame takes you to a position just in front of the trigger transmission pin, so that upper blind hole reaches back behind the location of the sear lever pivot pin in the inner barrel tube and a side hole in the inner barrel could be added there, but would this weaken the inner barrel tube too much being so close to the mechanism slot? Remember the inner barrel tube is the structural element that holds the gun together, a gun that is designed for 40 bar! New breather holes diametrically opposing existing holes carry less risk, but this is not possible in the "Mirage".

Personally I would not make any such barrel changes as you could destroy the gun and any structural failure at high pressure would have dangerous consequences, particularly if the gun was not submerged at the time. If you were redesigning the "Mirage" from scratch then the non-return inlet valve to the pumping barrel, including the valve seat, would be built into the partitioning bulkhead and would be independent of the rear handle thus allowing a more open architecture inside the rear handle, but that would not be the simple and rather elegant valve design we see in the existing "Mirage". There the pumping barrel inlet valve assembles from the rear of the bulkhead and has no joins that require extra sealing other than the "O" ring that sits on the seat, it is an inspired design. To assemble the inlet valve from the front of the bulkhead would require a spring retainer which would need to be inside the pumping barrel bore to avoid any external leaks which would negate the function of the pumping barrel by refilling it from the front tank instead of the rear pre-chamber. No doubt it could be done, but if you used a screw-in retainer that was also the boss that the pumping barrel sealed onto then it would require sealed threads and would also need to be aligned perpendicular to the bulkhead and on a parallel axis with the longitudinal axis of the gun. Maybe easier said than done!

 

[Diving Gecko]

Hi Pete,
Good thoughts and I don't think I would make an extra hole in the shooting barrel either.
But I am not sure I follow you on your last point about it being difficult to have the non return valve for the pumping barrel located in the partitioning bulkhead. As far as I understand, the only thing the white plastic bushing in my handle is doing is to the o-ring in place so the metal ball (pushed by pressure and spring) can seal against it. Instead of the bushing being located on the handle, it might as well be a threaded bushing in the bulkhead like the over-pressure valve. The air space that is behind the white plastic bushing in the handle is connected to the air space in the in the bulkhead anyways, no?

 

[popgun pete]

The threaded bushing in the over-pressure valve and the similar one in the rear inlet valve for adding pressure to the gun place the screw threads on the biasing spring (high pressure) side in conjunction with an enclosure without any joins on the "O" ring seat (low pressure) side of the valve, thus these one-way action "non-return" valves allow no alternate leak path through the body of the valve for high pressure air to move past the outer periphery of the valve seat and flow back to the low pressure side. The valve seat and the area surrounding it are one solid piece integral with the body of the valve. That is not the case with the pumping barrel inlet valve, but the existing design uses an immoveable valve seat which faces high pressure air and does not rely on screw threads to hold it in place as it sits in a stepped recess fronting a short bore or hollow space in the handle moulding (refer to attached diagram). The "retainer" holding the valve "O" ring on the valve seat is the entire partitioning bulkhead as increasing pressure acting on its front face as the pressure lowers on its rear face forces the partitioning bulkhead onto the handle moulding sitting behind it. This pressure differential tightly clamps the opposing flat surfaces together thereby confining the "O" ring which also seals peripherally in the small bore it sits in on the rear face of the bulkhead. If alternatively you screw the valve seat into the back of the bulkhead then the clamping action will be via the screw threads, not the pressure differential, and those screw threads will be resisting pressure of near to zero on one side and maybe over 40 bar on the other, all this on a small diameter thread. Not a job for plastic threads I would think even though the cross-sectional area facing high pressure air would be small. Remember that the valve and pumping barrel are close to the periphery of the bulkhead, so no room for using large diameter screw threads on either spring retainers or valve seats in this particular location.

Yes, you could do it with a screw-in rear valve seat, but with metal threads in a metal bulkhead and valve seat. To do it in plastic using a long threaded bush as a valve seat plug that would provides more threaded contact surface area over which to distribute the load may make this a possibility in the later bulkhead design, which at 29 mm is 11 mm longer than before. The valve seat plug then being somewhat similar to a long, hollow, fat grub screw which could be made of brass and screws into plastic threads in the bulkhead. However it would be easier if any screw threads were on the high pressure side (as on the high pressure side the screw threads only resist pressure from the spring tension) and not facing the low pressure side which is why I was suggesting that they be used at the front of the bulkhead with the rear facing end of the valve being a solid section with a small airflow hole in it, the same design principle used in the other non-return valve seats in the gun. The root diameter of any screw thread has to be at least large enough to pass the "O" ring through it and position the "O" ring on the valve seat.

 

[DANILO020]

hi folks, sorry sticking my nose......and sorry for my english as well...
I Have some mirages in my canteen and I tried some way to improve power as did not want to load the gun more than 32 atm....
I tell you what I did..

1) I found out that the oil inside the gun is a great obstacle to the air flux through small holes and narrow tunnels....
try this test: just pump 4/5 strokes with the lower barrel then, without loading the shaft, flip the knob to maximum speed... at that point you will hear some noises going on for seconds and if you do the same test without oil inside the gun you will notice that the air transfer will be immediate without any kind of noises...of course, to do that you need to dismantle the gun often, grease the barrels and using a piston with a small tank full of oil between the two oring and to be an happy spare compressor owner...

2) I drilled an hole (about 8/9mm) on the upper side of the barrel just like the other guns and then I milled a recess as deep as 1 mm as large as the hole starting from the hole towards the head....the recess should pass the handle for about one inches without getting close to the bulkhead....the recess in the top of the barrel should be made by using a small mill that goes back and forth in order to keep a deepness of 1mm constant from side ti side....

3) In the past I used to build the lower barrel 9/13mm and the upper barrel with 14mm bore in order to keep high power with low pressure...