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

[popgun pete]

I have sent a direct query to Mares via their "blog page" and asked them if such a gun is a possibility, referencing this thread, and whether the demand would be sufficient that such an investment in manufacturing the additional parts required would be considered. So if you want a "Mirage Evo", or something very much like it, then you better start writing in to Mares (Italy) via their web-site.

No demand, no product; so any "hidden demand" needs to be uncovered as they will require more than a few enthusiasts talking about the "Mirage" both here and elsewhere. That is a new and better breathing version than the old one was as the market now wants something along the lines of the "Cyrano Evo" with a modern handle, a big bore inner barrel and the ability to shoot both 8 mm and 7 mm diameter spears using spring stainless steel and better quality, longer flopper, spear tips.

 

[popgun pete]

A follow-up search of the Mares blog page https://blog.mares.com/ showed zero topics for pneumatic spearguns, so my message, which was acknowledged as "sent", must have been sent to somewhere else, such as the Mares trash bin!

 

[popgun pete]

It appears that spearfishing has been consigned (outcast) to a different Mares blog page. Maybe here http://spearfishingblog.com/tag/mares/ or here http://www.mares.com/en/sports/spearfishing/?region=us will be better places to write to.

 

[popgun pete]

Updated the schematic diagram to show the rubber sleeve tube valve at the rear of the pumping barrel. The ring of tiny holes allow air to be moved from the pumping barrel into the front tank once pressure in the pumping barrel builds up to a level which will expand the rubber sleeve, thus unseating the valve.

 

[lagfish]

For me, an ideal one size fits all, very last gun I'd buy spear gun would have the following characteristics:

• Length <= 1.1m: for ease of packing for travelling and can be easily tracked underwater
• Power adjustable to be able to take pelagic fish to 8m while able to adjust the power down when reef hunting / near rocks

Is it possible to design a pneumatic gun with the above? I think so. It would probably look something like this:

• Pneumatic (or hydropneumatic? Haven't lookied into that one yet), which provides more power for the length and because rubber is primitive.
• Some sort of way to provide enough power to get the pelagic fish to 8m. The limit for power on the one barrel for pumping/shooting is how strong the user is for loading it in a given position. The solution would be to allow multiple pump actions like the Mirage and/or using a different loading position for example using the legs/hips in a pushing motion (like squatting with a barbell). This is the reverse direction of how a pneumatic is loaded but can be done by putting a seal on a permanent loading shaft and reversing which side of the piston's air volume is to be compressed.
• For high power use, the spear itself would need to be >8mm OD and >1.1m in length in order to carry enough kinetic energy once the water resistance has slowed it down. A spear substantially longer than 1.1m that sticks out infront of the muzzle can be used if the gun is to be used on high power mode. I'm not sure what the implications on accuracy of this stick out is, but I don't think it's much. If you are accelerating a spear to the same energy over a short distance (due to length limitation of gun), you have to apply more force which will whip the spear more. However, this happens in bows and arrows and as long as it's repeatable it should be fine. The other option is to make the spear OD even bigger. You would have a nose-heavy gun but that can be remedied by a float. You can also attach the short shaft and long shaft together by screwing them. By having the connection ahead of the muzzle, you can still use a sealing vacuum barrel.
• Hydraulically softening the piston stoppage at the end of the shot or with a coiled spring because this thing is going to be a monster.
• For low power use, the spear could be 7mm OD or the same size OD as high power but perhaps with a hollow core so that it is lighter and still give you the shaft speed you need but does not destroy the tip with all the mass behind it once it hits rocks.
• Infinitely adjustable power on the fly. Instead of a selector knob, implement a screw adjuster. The airflow limiting / power adjustment manual valve (not sure what the proper name is) would need to be designed so that it has a large flow variation with respect to travel. The pitch of the screw would need to be high enough so that the pressure does not just push the valve open with a spring behind it. This way you don't need to ever adjust the pressure in the gun.

It would not be too difficult to build something like this one off. You can reuse many components off existing spearguns like the inner barrel, pumping barrel, pistons, trigger assembly (this one might need to be custom made to withstand the high piston force), vacuum muzzle. The receiver and handle are parts that would be tough to machine but you can 3D print them with SLS using Nylon and the tolerances/surface finish will be good enough for O-ring sizes larger than CS 1.5mm. For power adjustment, you would be safe in pressing in/epoxying a metal sleeve that provides the sealing surface.

I've been reading everyone's (PGP's especially) notes on these guns while I was bored on a plane and wanted to contribute some of my own ideas.

 

[popgun pete]

You need a long gun for the sighting radius and the necessary axial length for accurate, intersecting convergent line shooting (i.e. "shoot from the hip") and a short gun for up close and confined areas. That is two guns. If you spear in densely vegetation obstructed environments where you need to weave your gun through a curtain of branches and stems and thus mount a sneak attack on an unsuspecting victim then you need a long thin gun, but no longer than is necessary to bridge the distance to the victim. So that is three guns.

Every possible idea has been tried since the first pneumatic guns opened fire in the 1940's and no stone has since been left unturned. The hydropneumatic gun is very versatile, but it has a problem in not being a floater unless the gun is long enough to fit it in a buoyancy jacket. Another problem is that with saltwater inside them the potential for internal corrosion and jamming is very real. Many hydropneumatic guns ended up in a junk box when the owner belatedly realized that the instruction book might have been worth reading after all.

The pneumatic gun is much more efficient than the hydropneumatic gun and the vacuum barrel guns even more so, plus they float after the shot which is very desirable in order to keep them up off the bottom. Hence the ideal weapon is the pneumatic gun with a dedicated vacuum barrel system and a partitioned reservoir power regulator system designed to not the choke the gun when you select "full power".

If you want to shoot monsters then you need a specialized gun which is not much use for anything else, but can be loaded for the low number of shots required without absorbing too much time, but plenty of your energy, without draining you completely as you still have to dive, aim and shoot and hang on the capture system in order to drag the victim back to, and up into, the boat.

 

[lagfish]

Why does a hydropneumatic gun allow a slimmer design? Because of a smaller inside barrel and allowance of a higher compression ratio since you can do multiple pumps per shot?

 

[popgun pete]

You need to read this thread and then you will have your answer: https://forums.deeperblue.com/threads/pneumatic-speargun-compression-ratio.86054/

 

[lagfish]

Pete,
I've read through most of the thread and here's what I got and my own thoughts, let me know what you think:

1. The limitation on the power of a gun is the user's ability to load the spear which is a factor of the strength of the user for a required loading position and whether the shaft will buckle. This limitation for strength is (assuming that the maximum force output of the user is constant throughout the loading range of motion) the area of the piston times the highest point on the tank pressure vs. piston travel curve. Limitation for shaft bending does not have to be that point if the shaft is supported by the muzzle, which will shorten its effective buckling length as the shaft is pushed in as it's loaded.
2. The gun should be as efficient as possible as to not raise the diver's heart rate and oxygen consumption needlessly. Efficiency means putting the right amount of power into the victim (not more than necessary) and using the least amount of loading effort.
3. Higher compression ratio guns have the advantage of being smaller due to reduced tank diameter but for the same maximum force required to load it, imparts less total energy on the shaft because the pressure is reduced faster as the barrel volume increases when shooting (more slope on the pressure vs. travel curve). However, the efficiency of the user to spear energy transfer system is not affected by the CR assuming everything else is the same.
4. If you can provide a mechanical advantage to break up the loading effort by increasing the total work distance, the disadvantage of a low CR gun largely disappears. The "lever" can always be set so that the maximum loading force is manageable for the user, and the efficiency will not suffer, assuming the gun's design has good efficiency (not true for the Black Sea, true for the Mirage). Will the time to load the gun suffer as a result of the increased work distance? I think not by much. The force-velocity relationship of muscles means that as the force produced by a muscle decreases, the time required to go through the same range of motion is reduced (https://upload.wikimedia.org/wikipe...025746!Muscle_Force_Velocity_relationship.png). As an example, if a athlete's maximum bench press is 315 lbs, he should be able to bench 275lbs/3=92lbs for 3 times about as fast as he can bench 275 lbs (87% of max) once.
5. One source of inefficiency is the gun having too much power for the hunting conditions encountered on a specific site/time. If there is only two "gears" for on-the-fly adjustment of shooting power, then the user is almost always using more energy to load the gun than is necessary. More gears or a "CVT" power selector would increase the efficiency of the total user-to-victim energy system. Of course the user can carry multiple guns on a dive to account for different conditions, but it's a fun exercise to come up with the concept of a do-it-all UPS - Universal Pneumatic Speargun.
6. Another source of inefficiency is that certain muscle groups are more efficient at using oxygen than others. The leg muscles for example are much more efficient than the arm muscles (https://www.ncbi.nlm.nih.gov/pubmed/1934942, http://fasterskier.com/fsarticle/ar...t-improving-ski-technique-can-help-lazy-arms/). By optimizing the loading positions so that the most efficient muscles are used, is another potential way to improve the user's bottom time. Whether or not a position like this produces a practical design remains to be seen.

 

[popgun pete]

Well I am not going to go through everything point by point, but the efficiency issue with the gun itself is due to losses in the storage medium and friction between moving parts. Rubber bands are not ideal energy storage devices as they lose energy by virtue of the stretching creating heat that is not recovered when they contract. But they don't rust, unlike metal coil springs. When you compress a column of air you get adiabatic heating, but the losses there are nothing as the compression ratio is too small to have any real effect.

The "Mirage" is actually an inefficient gun as when you use the pumping barrel to load it the pressure in the gun is driven higher than the "cocked to shoot" pressure, but you throw that energy increment away when you flip the power regulator knob up in the selector gate to send it flying back to the full power position 3. The advantage of the "Mirage" is the gun can be loaded using high pressures that would be virtually impossible to do otherwise without bending the shaft, if it was a slim one (7 mm dia.), and it allows you to latch the gun without turning yourself inside out. The downside is that the fish may have gone by the time you are ready for the next shot!

A highly efficient pneumatic gun is the Russian "Taimen" as being a very small and compact weapon it seeks every energy loss minimizing refinement to make the most of its limited capacity to store energy by virtue of the gun having a small volume compressed air tank, a tank size that is necessary for the hunting environments that it was specifically designed for. The inner barrel of the "Taimen" is polished like a mirror and the tiny piston has one seal, the gun being made with the precision of a wristwatch in terms of very small and light weight parts.

 

[lagfish]

Isn't piston to barrel friction minimal due to hydrodynamic lubrication?

 

[popgun pete]

Isn't piston to barrel friction minimal due to hydrodynamic lubrication?

It is low, but not zero. Tests have shown that more piston seals do make for a slower shot, but it is not really obvious until you shoot the same gun with different pistons. I have and the three seal piston gave a noticeably lower tug when the spear hit the end of the shooting line compared to the gun's original piston, however the original units could no longer be obtained as they had long been out of production (about 20 years in fact!).

 

[popgun pete]

Another possibility for a new "Mirage" speargun is to abandon the hope of using existing parts from the current Mares range of pneumatic spearguns and switch to a thin wall, stainless steel inner barrel tube with a 14 mm diameter bore. That would require a new inlet valve body and muzzle which were threaded for the finer pitch threads now used on the inner barrel ends, stainless steel offering the thread strength without the depth of metal required on alloy inner barrels. A thinner wall stainless steel tubing could also be used for the pumping barrel, but that still requires a 10 mm diameter bore in order to swallow the 9 mm diameter shaft tail stops on 8 mm diameter spears. With these thinner barrel tube walls it may be possible to cram two barrels into the existing "Cyrano Evo" handle in terms of its main barrel offset from the gun's longitudinal axis with respect to the outer tank. A stainless steel inner barrel would lend itself to polishing "to the mirror" as is done with the Russian "Taimen". Thin wall stainless steel tubing would allow the gun to still be a floater and possibly the new gun could be equipped with titanium pistons in order to make better lasting pistons that will not crack at high impact velocities on matching anvils. Unfortunately the purchase price of such a new and highly revised gun may then be heading for the Stars!

This new 14 mm bore "Mirage Evo" speargun would be created as a pneumo-vacuum gun in order to avoid pumping a 14 mm diameter annulus of water out with the spear on each shot from the main barrel.

 

[Diving Gecko]

As I am pretty much on a daily basis thinking about my own take on this challenge, and have been for a while, I have pondered the 14mm ID shooting barrel also. Mostly since it seems I can get it off the shelf in the BA (bright annealed) finish which is already very smooth (though just a few days ago, I might have found some 13mm bore tubes, too).
I wouldn't suffer from space constraints in a handle (as I would either make my own or use a Mirage handle) but a 14mm shooting barrel would help A). Lower the overall pressure in the gun and place less stress on the structures and B). Create a tad more of a pressure differential between the loading and shooting barrels, making loading at higher charge pressures even easier.
In theory, a 14mm piston should be a disadvantage as it would likely weigh more and the o-ring surface area would be bigger resulting in higher friction, but I am hoping it is negligeable in the real world and that the smoother bore would make up for it.

 

[popgun pete]

The 14 mm diameter main barrel is to increase the force levels on the spear, not lower the pressure inside the gun. There being a larger difference between 14 mm and 10 mm than 13 mm and 10 mm in terms of cross-sectional areas of the main and pumping barrels a new "Mirage" would be even more useful with a 14 mm diameter main barrel. While you can just load a 13 mm diameter inner barrel gun at 40 Bar using a double handed loader and taking care not to bend the spear, a 14 mm diameter main barrel would be a step too far. If the spear could be inserted deep into the barrel and only then spear muzzle loading started then the spear is much less likely to be bent. That is how the "Aquatech" hydropneumatic guns work, but they use much smaller ID inner barrels being only about 1 mm larger than the shaft diameter.

Why spearguns with 14 mm diameter inner barrels disappeared is most of them used spears that had tails that matched their often unique pistons, for example GSD pneumatic spearguns used ball tail ended spears that were grasped by nylon jaws on the piston nose. Many divers bought the gun with its single spear and once the spear was lost their gun was useless. The GSD distributor here was keen on selling guns, but not offering any spare parts, including spears. Contrast this with "Airdive", the then Mares distributor, who had spare shafts available for supply to shops and I had many spare shafts for my "Sten" gun models as a consequence. A number of those shafts are now on the bottom somewhere as they parted company with the shooting line under moments of duress.

 

[Diving Gecko]

I can only speak for myself on the matter of loading but I can't load a regular oleo at more than max 23bar, I might be a pussy or have bad technique. As such, and for me, 14mm would not be about having more force on the piston as I wouldn't be able to load it anyways;-).
Once in a while, I do read about some guys loading at really high pressures though I believe the vast majority load their guns at 18-25 bar (13mm piston). I am a small guy and others are strong as horses but I think I'll do a poll on this, it would be interesting info for us all to have

At one point, I actually thought about changing the loading barrel in my Mirage to one with a 9mm bore but that would exclude me from using 8mm spears with tail ends and in the near future, I will start experimenting with 8mm shafts on my bigger Mirage. It seems to shoot with a lot of power but compared to many bandguns the shaft is still very short. My longest, custom Mirage 125 shoots a spear that would correspond to only 95 in bandguns. S0, going to 8mm if the gun can put it out with enough speed, is a way to mitigate the difference. Maybe even 8.5mm further down the line - talking bluewater Mirage, here.

Cool option in the Aquatech with the possibility to only use the last part of the loading stroke where the spear is the most supported. With my 90, with the 6.75mm spear, the middle part of the loading is almost as challenging as the part just before latching.

 

[popgun pete]

I added this to the Inalex "Alpha C1" thread, but it is also pertinent here.

"The advantage of a 14 mm diameter inner barrel gun is only 16% compared to a 13 mm diameter inner barrel gun as 14^2/13^2 equals 196/169 which is 1.16. In the sixties and seventies the majority of pneumatic speargun were 13 mm or 0.5" as that was the "standard", but more expensive guns such as the GSD models had 14 mm diameter inner barrels using their increased power as a selling point. A similar calculation for 13 mm and 11 mm inner barrels gives the answer as 13^2/11^2 equals 169/121 which is 1.40 or 40% improvement. Not surprisingly divers find those 11 mm diameter inner barrel guns easy to load, especially if they are stepping down from 13 mm guns."

 

[popgun pete]

A direct comparison of proposed "Mirage Evo" and the "Cyrano Evo". Note the piston tails.

 

[popgun pete]

To complement this thread I have ran an analysis on the pumping barrel operation of the "Mirage" format spearguns and the effect of an increase in main barrel diameter here: https://forums.deeperblue.com/threa...ge-spearguns-pumping-barrel-operation.107763/

 

[popgun pete]

Comparison of gun layouts using pumping barrel system for incremental loading at high start pressures.