Russian "Neptune" Speargun

[popgun pete]

It looks like the "Neptune" pneumatic speargun is going to be back in production as a new web-site has now been created for it. http://www.neptuntula.ru/

The "Neptune" design is based around a mid-handle pneumatic gun which is claimed to float after the shot. It has a "powerdial" power regulator and a power-operated line release arm at the rear end of the gun. I tried to buy one of these guns some years ago and just as the purchase details were being finalized the project fell over!

The guns had been sold in some quantity, but their quality was variable and that eventually put an end to it, however the fix was that it needed more experienced people to make it rather than saving on the workforce costs. The photos here are from the old web-site http://www.neptun.tula.net/page_eng.html

A photo from the new web-site shows the right hand side of the gun, which is the side on which the line wraps are installed.

 

[popgun pete]

The "Neptune" has an off-central axis, cam lock trigger mechanism as can be seen in this manipulated image based on Hanter's photos. Note that the sear tooth is actually a gear wheel and it interacts with a piston tail that has multiple flanges like a gear rack (the piston is not shown). This piston tail, gear toothed rack revolves the gear wheel sear and thus the sear lever arm and locks the trigger mechanism when the piston is pushed right back into the gun. The gear wheel also meshes with another rack that is on a reciprocating rod installed inside the rear housing, the rear end of the rod bearing yet another toothed rack that drives a gear toothed sector on the base of the line release arm. Hence as the gun shoots the revolving gear wheel "sear tooth" also powers the line release lever to let go of the line wraps. Very clever, but everything needs to be precisely made and fitted for it to work smoothly.

 

[popgun pete]

The "Neptune" gun specifications are shown in this table.

 

[popgun pete]

More information is available on these annotated photos.

 

[popgun pete]

We can work out how the "Neptune" operates its power-operated line release by looking at the number of teeth on the gear wheel "sear tooth" and those on the rack ends of the rod that engages the gear wheel and in doing so moves the rear line release lever as the gear wheel turns. The gear wheel has 7 (not 8 as I first thought) teeth and the two sets of rack ends on the rod have 4 teeth if you count the tooth at each end of the rod, but the drive action will involve the three gaps between these teeth as there are 3 teeth on the curved sector at the base of the line release lever and 3 teeth on the piston tail rack which in a sense is a series of mushroom head flanges clustered one immediately behind the other. As the line release lever projects vertically outwards from the right hand rear side of the gun in order to wrap the shooting line on it, then it must travel through about 90 degrees to release that line and therefore the gear wheel "sear tooth" must turn through that same angle to drive the linking rod that connects them both together via the gear teeth meshing at each end.

Hence for the "Neptune" to work properly the piston has to be pushed down the inner barrel until it engages the gear wheel "sear tooth" and then as the latter turns to fully engage the piston tail it simultaneously hauls in the linking rod that is connected to the line release lever at the rear end of the gun causing it to elevate up and away from the gun body. As the trigger mechanism locks the line release lever reaches a position fully perpendicular to the body of the gun. Now the linking rod is exposed on its ends to ambient pressure at its rear end and gun internal pressure at its inner end (the rod carries two "O" rings with a gap between them in the central section of its length), so hauling that linking rod inwards during cocking of the gun requires some effort to move it against air pressure trying to move the linking rod back the other way. Conversely when firing the gun air pressure is pushing the sliding piston out of the inner barrel and also pushing the rod backwards to roll the line release lever back flush with the side of the gun. The gear wheel "sear tooth" therefore has to mesh perfectly with the two respective sets of gear teeth engaging it on two sides without jamming or binding on either, and hence it is obvious that everything has to be very well made for this system to work properly or parts will jam and possibly break.

All this manufacturing complexity to power-operate the rear line release lever, and have a "Powerdial" system of revolving alternative airflow ports inside the rear mechanism housing block as well, makes for an ambitious and very expensive gun to produce.

The recent version with the passive line release clip at the rear may make for a more reliable gun as the linking rod can be deleted and at least one potential source of air leaks, i.e. through the tunnel or bore that the linking rod slides in, can also be deleted from the gun. However the gear wheel "sear tooth" is basically there to operate that linking rod, so I don't know if it has been retained in the simpler version of the gun or not. From a production parts requirement perspective it is most likely still being used.

I have been looking for a schematic of the "Neptune" gun, one was available on-line in the past, but now seems to have disappeared. I have a printout of it somewhere, but the resolution is not the best and I have yet to locate it in my files. (Have now found the patent instead!)

 

[popgun pete]

The old advert for the gun.

 

[poildeq]

Wow man that is what engineers do to pass the time

 

[popgun pete]

"Wow man that is what engineers do to pass the time".

Part of the evolutionary process to improve the performance of underwater weapons. However not all designs end up being "improvements" as at some time the gains made have to be weighed up against the effort required to produce them and the actual change in utility of the weapons for users. If most of the time the additional features do not add to the performance required in the majority of situations then the "new" designs fall by the wayside. A classic example is the Mares "Mirage", a very interesting gun technically, but ultimately not a great improvement on the "Sten". I speak from experience on this matter having used and repaired both of them. Everything I shot with the "Mirage" could equally have been shot with the "Sten", the "Mirage" being slow to load and only having an advantage with the gun pumped to 40 atm (or 40 Bar).

 

[popgun pete]

How the rear line release operates; air pressure inside the gun drives the linking rod rearwards as the gear wheel "sear tooth" disengages from the piston tail.

 

[poildeq]

Indeed popgun pete in enginerring circle we refer to it as a solution looking for a problem

 

[popgun pete]

Indeed popgun pete in enginerring circle we refer to it as a solution looking for a problem

The problem (perhaps also an obsession) being "solved" here dates back to the Soviet era "RPS-3" (РПС-3) which was a very desirable item in a market then starved of quality, mass production spearguns (diagram is attached). It looked good and had an intriguing layout which generated a lot of interest as it owed nothing to guns that preceded it, unless you looked very carefully for antecedents elsewhere. One quirky aspect was that the automatic line release controlled by movement of the trigger could lose its adjustment and an owner would look on in exasperation as the shooting line unexpectedly snapped and the spear disappeareed into the weedy bottom and was lost forever, short of a miracle in finding it again. That and the slim chances of easily replacing it caused many divers to be wary of mechanical line releases unless they were designed to be virtually foolproof. Bear in mind that the use of mid-handle, relatively short guns in their hunting environments had generated the view that the line release lever should be positioned at the rear end of the gun (to maximize the wrap length) and that passive line clips would not provide the necessary tension to the line wraps that were usually strung along the top of the gun, or slightly off to one side.

You can see the emphasis on powered, rear line release systems in many Russian and Ukrainian speargun designs even today and the "Galatea", subsequently renamed as the "Neptune", was to be the ne plus ultra of these designs coming as it did from Tula, the Arms Capital of Russia. It aimed to be the pinnacle of speargun design, but this meant that the gun had to be made with the precision of a gearbox and not the usually more sloppy fits found in a pneumatic speargun. If you have had any experience of gearboxes you will know that shaft alignments and meshing of the gears mounted on them is paramount. Get it wrong and things don't work as the intercomponent friction goes way up, so gears have seldom made appearances inside spearguns. With sufficient attention to detail such devices can be made to work, but in the desire to churn them out standards sometimes fall and then problems arise, especially for owners who lack the knowledge or means to correct any faults. Having bought one of the most expensive spearguns available in Russia there were some unhappy owners at times if they by chance had been sold a less than perfect example.

Hopefully these problems will be eliminated in the new production as for me the most interesting aspect is the "Neptune" gun is a floater (albeit in aluminium and without the optional adjustable sights would be my guess), something rarely encountered in mid-handle pneumatic guns of the past as a requirement for them to float was not a priority.

 

[popgun pete]

I finally located the printout of the actual "Neptune" speargun schematic diagram which I had fortunately kept and have now scanned it for inclusion here. Most notable difference to the patent diagram, if this schematic is accurate, is that the linking rod or rack is angled in the rear mechanism housing and not parallel to the inner barrel bore. Boring the channel that the linking rod reciprocates back and forth in parallel to the gun's longitudinal axis would have been reasonably straight-forward, but boring it accurately at an angle to that axis must have ramped up the difficulty in machining this housing component as the component has to be repositioned or the cutting head axis moved, although a multi-axis milling machine was probably used to generate the part. This diagram may still be on the web somewhere, but I have not been able to find it again, so for now this example will have to do.

I have now found the web reference where the "Neptune" speargun schematic that I had printed out some years ago came from, it was one of these two, but clicking on them produces no download and only a blank page results. Possibly their contents have been deleted, but they may resurface at some later date.
http://apox.ru/blog//5-Ryjya-dlya-podvodnoi-ohoti/217-ruzhe-qneptunq
http://apox.ru/blog//5-Ryjya-dlya-p...he-dlya-podvodnoj-oxoty-pnevmogarpun-qneptunq

 

[popgun pete]

By creating a rear projection of the gun, as it is shown on the patent diagram, it appears that there is insufficient material to mount the rear line release lever's pivot pin with it positioned so close to the periphery of the outer tank wall. My guess is that to create more room for mounting this component the decision was then made to angle the linking rod with a rack at either end and therefore mount the line release lever's pivot pin closer in to the longitudinal axis of the gun.

 

[popgun pete]

I used trial and error modifications to the patent diagram and an angle of 4 degrees for the link rod seems to be about right, assuming the proportions of the patent diagram are true to the actual gun's dimensions, or close enough for what is of interest to us here.

 

[popgun pete]

Using the exploded parts photo from Hanter's web-site I have tried to match the components with their counterparts on the speargun's schematic diagram. From this arrangement we can see that the "Neptune" has a very different construction, the front pressure bulkhead is held onto the inner barrel tube with a special nut and the outer nose cone screws onto the bulkhead using a screw thread on its periphery to join those two sections together. Hence, unlike other pneumatic spearguns, the "muzzle" is actually a separate outer nose cone which sits outside the pressurized section of the gun and it is the special nut that clamps the gun together at the front end, rather than the "muzzle" providing the nut function which is the usual arrangement. The tube spanner supplied with each gun (it also functions as a screwdriver handle) is used to remove this nut and is shown at the lower left of the revised diagram.

 

[popgun pete]

It occurs to me that we can work out what the buoyancy of the "Neptune" aluminium gun is if we can assume that the titanium version of the gun has the exact same water displacement as the aluminum version. The 830 mm length titanium gun weighs 1.3 kg and has a negative buoyancy of - 0.15 kg which means that the "upthrust" caused by the displaced water is 1.15 kg. Now the aluminium version of that same gun weighs 1.1 kg, so in water it will weigh 1.1 kg minus 1.15 kg which gives it a positive buoyancy of 0.05 kg. Using the same calculations for the 630 mm and 510 mm guns yields a buoyancy figure of 0.1 kg for them both, although rounding of the figures in the specifications table may obscure any slight variations between those two models. Generally the longer a gun is then the buoyancy situation improves as any tubular additions to a gun's length add more water displacement without a proportional increase in the gun's mass, the higher density elements of the gun's construction remaining the same length, such as at the muzzle and mechanism locations, but here the longer gun is less buoyant, unless there is something "missing" in the data in the table due to rounding up or down of the displayed figures.

 

[popgun pete]

I am ordering a "Neptune" 80 cm speargun in aluminium as it will be a floater and have decided to include the adjustable sights option. Here I have stretched the diagram to give a better appreciation of the "Neptune" speargun's dimensions.

 

[Diving Gecko]

Such an interesting gun. That rack gear line release solution is really swank. I like the idea of the rear sight, too.
Do you happen to have anything showing the trigger in detail? Some drawings show a piston with a "gear" on its tail, some show a more normal "mushroom" tail, so I am still a bit in the wild on the trigger itself.

 

[popgun pete]

Post #2 and figure 3 of the patent drawings show how the trigger operates which is rather complicated as it is a cam locking system, not a rocking system as you have in most pneumatic spearguns. Note the locking arm indicated on the annotated trigger mechanism housing photo. Using gear forms where linear motion of one part also converts to rotational motion of another part is very clever, but the gears must mesh and turn easily or you will have a wagon load of problems. Busted pistons when the gear form “stacked mushroom” tail jammed were one manifestation of things not being quite right in the construction quality of the gun (this I should add was well over a decade ago) . Hopefully these problems are in the past with a lift in gun quality from the Tula masters.

 

[popgun pete]

In an earlier attempt at reaching a wider market the Russian "Neptune" was sold through Esclapez in France as the "Murena" in both aluminium and titanium versions. The alloy gun being a floater after the shot it should have succeeded, but when the venture collapsed few guns would have made it into the hands of users. Here is a photo of a "Murena" and in an eBay auction for a titanium version the seller posted pages from the owner's handbook which I saved and now add here for the reader's interest.