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Old 11-18-2012, 05:57 PM   #1
popgun pete
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A Different Evolution

This is the hydropneumatic РПС-3 (RPS-3) speargun from the Soviet-era. The attached article (translated from the original Russian) describes in a very concise manner exactly how the gun operates. A careful reading is required as the authors assume you take on board what is said in each paragraph, they don't explain anything twice, so you need to pay attention.

The gun was produced in the Ukraine, which was then part of the Soviet Union, from about the time of this article (1978), having had prototypes tested for five years. The РПС-3 gun was only produced in the shorter length (inner barrel tube length was only 40 cm instead of the 70 cm shown on the drawing) as the changeover system of alternative longer inner barrel and outer tank with spear never eventuated from the "Vega" factory. The Mares "Sten" rear handle pneumatic gun was already around when this gun was formulated, the Italian made "Sten" is a product of the late sixties, so this Soviet-era gun has tried to be totally different in its mode of operation and construction. It certainly succeeded in being very different! The small version of the gun was produced for about twenty years, while the complicated metal fabrication work was very good, many internal steel parts were only plated against corrosion and the seals were made of a rubber compound that fractured easily, had bad oil swell characteristics making it expand and soften too much and the molded rubber rings were encumbered with heavy untrimmed flash.

Because the gun sealed on the spear sliding through a stationary muzzle seal rather than a spear tail mounted seal sliding inside the inner barrel tube the surface of the spear was a critical sealing element. Usually the inner barrel bore is the critical sealing element where, unlike the spear, it is protected from collisions with the environment (rocks, sand, grit, etc.). If the rubber muzzle seal had a slow leak then you found that when you pulled the trigger nothing happened as water under pressure had escaped from the gun with no visible sign of its departure since you muzzle loaded it. A form of reverse "Russian Roulette" for the fish.

With few molded parts and a lot of machining required for each gun they would have been expensive to make, so not surprisingly the design was not taken up by anyone else. The guns don't float after spear discharge. Neither gun in the attached photo currently works, so I have no idea how they shoot, but firing a 9 mm OD shaft is asking a lot from such a small gun. Shown here purely for interest in a different evolution where thinking has gone "outside the square", requiring considerable ingenuity and effort in making an unlikely idea work, well some of the time anyway!
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Old 11-18-2012, 10:35 PM   #2
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Re: A Different Evolution

How the РПС-3 trigger mechanism works, surely one of the most novel trigger mechanisms ever used in a speargun. Based on the original drawings by skarabey, I have added an additional step and shown the angled sear tooth (60 degrees) inside the sear disk. Pulling the trigger withdraws the sprung loaded boss on the RHS and the mechanism reverses the sequence shown for loading the gun with the spear shaft tail pushing the sear disk aside. That is why the sear tooth and spear tail have angled faces, they drive the sear disk vertically in the gun for latch and release. The sear disk movement up and down is only 1.5 mm! By encircling the spear tail's rear cylindrical stub the sprung loaded boss stops the spear tail jumping the sear tooth when the mechanism is locked up as shown in position 4. The horizontal coil spring pushing the boss is strong enough to stop internal pressure firing the gun on its own, but not so strong that your trigger pull effort aided by this internal (hydrostatic) pressure will need to be any greater than usual for a speargun. Except for the compressed air reservoir the gun is full of water when in use, so it sinks like a stone when you drop it.
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Old 11-19-2012, 04:21 AM   #3
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Re: A Different Evolution

I'm certainly glad this method of spearfishing didn't become popular. I much prefer a piece of wood, some tubing and a trigger. Pretty neat though!
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Old 11-19-2012, 08:11 AM   #4
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Re: A Different Evolution

Dont let the lack of knowledge and understanding lead you to believe these guns are not popular. Pneumatics are great, they just require a different techniques and methods to make them work properly, and they preform very well when modified.

As always, Popgun, Thank you for todays history lesson

Last edited by kwtony; 11-19-2012 at 08:28 AM.
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Old 11-19-2012, 08:28 AM   #5
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Re: A Different Evolution

Good Info Pete!

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Old 08-22-2013, 07:53 PM   #6
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Re: A Different Evolution

These diagrams show how the "RPS-3" trigger mechanism pulls the boss that releases the sear disk and then automatically applies the safety mechanism when the shaft is relatched for the next shot. (Finally got around to doing them.)

This photo shows the trigger after the shot, but before cocking the gun, so is as shown in the lower diagram. Note the rust!
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Last edited by popgun pete; 09-30-2013 at 07:22 PM. Reason: more info, adding a photo, production gun diag.
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Old 10-06-2013, 07:27 PM   #7
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Re: A Different Evolution

Here are the Specifications or Technical Characteristics for the "RPS-3" speargun, taken from the original Russian User Manual.

Technical Characteristics
Range shooting underwater with chamber pressure 6.2 - 6.5 MPa, not less than 4 metres
Effort when charging adjustable from range 200 to 400 Newton (20.4 to 40.8 kg)
Overall Length of gun with spear: 85 cm
Weight of gun with spear, not more than 1.3 kg.

A range of 4 metres (13 feet) seems pretty good for a short speargun, until you think about just what those numbers actually mean.

As stated earlier, the inner barrel length of the production model is 40 cm, which is also the "working stroke" of the spear. Although the inner barrel's ID or bore is actually 10 mm, the effective bore is 9 mm, which is the OD of the spear shaft, as the gun operates on a volume displacement principle with the body of the spear displacing water into the air reservoir space or pressure chamber as the spear is inserted into the barrel. Displaced water is kept separate from the compressed air by the rubber pipe or tube acting as a flexible partition, unless it or some of the rubber seals leak which they have been known to do.

As 10 bar equals 1.0 MPa (Mega Pascal), that is 62 - 65 bar (or 63.2 - 66.3 kg/cm2) of initial chamber pressure! According to the User Manual it takes from 100 to 140 pump strokes to achieve a pressure level in the chamber ranging from 4 to 6.5 MPa which will allow the gun to shoot "as far as" 4 metres. A pressure of 65 bar is equal to 943 psi! To put that in context a carbon dioxide gun operates at 900 psi, yet you don't muzzle load it against any pressure or pump it up.

Further on in the User Manual a reminder is given that the user "ought to consider that when the stated (max) pressure is used in the chamber then for loading the spear in the barrel with the hand loader it is necessary to apply an effort not less than 380 Newton". That is 38.7 kg or 85 lb of force to get the spear started moving in the inner barrel with just one hand (maybe two if you can risk taking your steadying hand away from supporting the barrel)! No doubt many users opted for an easier life by using lower chamber pressures and settled for less range, especially when considering the pumping up of the gun to that pressure level to begin with. Even with the novel system of the hand pump clamped by a rigid metal yoke fitting across the gun body at right angles and the gun itself used as a giant pump T-handle it is not easy to do. The idea is that you can throw your body weight into the pumping action at higher pressure while your feet anchor the folding tubular pump handle on the floor, the pump rod remaining stationary while the pump and gun move up and down.

The production "RPS-3" gun was later found to have an efficiency of 35%, which is relatively low for a pneumatic speargun and not a good return for the energy expended in using it at maximum pressure, particularly if that loading effort "evaporated" through the easily damaged muzzle seal due to invisible leaks underwater before you pulled the trigger.
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Old 10-07-2013, 04:48 AM   #8
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Re: A Different Evolution

I remember buying these guns when we were kids and my dad was a diplomat in the x-soviet union. Those guns would be good for only a couple of trips and then they would stop working. They were extremely cheap so you could buy a few of them and not worry about fixing them, but the quality and workmanship and fitting was incredibly poor. I don't think these guns can be compared to some of the high quality pneumatic guns from Mares, Sporasub or Salvimar, let alone guns that are custom modified for dry barrels, but they were the only guns available for us at the time and I did shoot some fish with them. I also favor rubber banded guns over pneumatic, but for extremely small sized guns where you are sticking your arms into holes and shooting, they do a good job. But with rollers now popular, a roller banded gun can be made quite compact and carry just as big a punch.
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Old 10-07-2013, 07:34 PM   #9
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Re: A Different Evolution

Quote:
Originally Posted by spearq8 View Post
I remember buying these guns when we were kids and my dad was a diplomat in the x-soviet union. Those guns would be good for only a couple of trips and then they would stop working. They were extremely cheap so you could buy a few of them and not worry about fixing them, but the quality and workmanship and fitting was incredibly poor. I don't think these guns can be compared to some of the high quality pneumatic guns from Mares, Sporasub or Salvimar, let alone guns that are custom modified for dry barrels, but they were the only guns available for us at the time and I did shoot some fish with them. I also favor rubber banded guns over pneumatic, but for extremely small sized guns where you are sticking your arms into holes and shooting, they do a good job. But with rollers now popular, a roller banded gun can be made quite compact and carry just as big a punch.
The "RPS-3" spearguns cost 55 rubles, that was the officially set list price and was actually displayed as such on the thermal embossing on the gun's vinyl carry case and was also permanently molded into the left hand side of the rear plastic handgrip as raised lettering. That price did not reflect the cost of making the gun, its manufacture appears to have been driven by non-economic decisions and the desire to make a technically innovative weapon that had a certain wow factor by being very different to that which had been done anywhere else, user feedback was probably largely ignored and the guns churned out according to production quotas, not demand. I have been told that the "RPS-3" gun was desirable because it was largely unobtainable, unless you were a Party official or had some "contacts" who could arrange the supply of a gun for you. Remember the Soviet Union was a Command Economy, not a Market Economy, so prices were set by the State and production volume of consumer goods was decided by Party officials and bureaucrats. Some near new "RPS-3" guns still survive because they were never used by their recipients who wanted a gun because they were in a position to buy one, probably more as a trophy item and validation of their status. Being a diplomat your Dad probably had access to the guns which was denied to many Russian divers who were starved of spearguns unless they had the means to make their own underwater weapons. That eventually gave rise to a "home-made" gunsmith tradition where there are many complicated designs that strive to be very innovative, few are commercial mass production propositions due to their manufacturing cost, but are purchased for the pleasure of ownership and having something different. The same drivers are at work here, only the band gun is the weapon receiving the most attention, just look at the custom speargun builders contributing on these "All About Guns" threads.

The "RPS-3" speargun produced in the Ukraine factory did not appear to survive the demise of the Soviet Union, however a production run of about 200 guns were later built in Russia that returned to the original design concept of a hydropneumatic speargun with interchangeable barrels and spears to create both a long gun and a short gun. Parts could be exchanged with the air reservoirs still pressurized, the rear handle assembly is only part of the gun's hydraulic circuit, not the compressed air reservoir which is completely independent. I doubt that these later guns were cheap to make or buy, my thoughts are that they were seeking to realize an opportunity otherwise lost.
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Old 10-08-2013, 01:31 AM   #10
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Re: A Different Evolution

Hi Pete, actually you could just go to the store and buy them. But at the price they had I guess it was too expensive for your typical Russian. The official ruble to dollar rate was 1 ruble = $ 1.20 ... or something like that. This had nothing to do with the real monetary value of the ruble but rather a cold war political statement showing that the USSR money had more value than the USA denomination. However a diplomatic ruble, which was a special denomination made for diplomats to allow them to access special stores that allowed imported items was worth 15 normal rubles and on the black market $ 1 would buy you around 4 rubles. So you can imagine that for diplomats buying stuff at local Russian shops it was almost free. You could actually buy jewelry with real high quality diamonds and 18kt gold for next to nothing, and many a diplomat made a lot of money by simply using his hard currency to buy such items. Communist USSR was really something, I will never forget the few years we spent there. You cannot imagine the misery that a human faces under communist rule.
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Old 10-08-2013, 04:02 PM   #11
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Re: A Different Evolution

Here is a composite photo of the later realization of the gun displaying it in the long and short versions obtained by swapping the barrels and spears. The hand grip shape is similar to that of the prototype design, but now has an added projection behind the line release lever. The shooting line is wound back and forth on the top of the gun. I don't know anything about this version's performance.
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Old 10-25-2016, 08:08 PM   #12
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Re: A Different Evolution

I am returning to this thread as there was still some unfinished business with the PПC-3 hydropneumatic speargun; i.e. why was the production gun so inefficient (at only a paltry 35%!) when the prototype PПC-3 guns were so promising during the field tests? The answer lies in the shortening of the gun's barrel and thus the “working course” of the spear as the inner barrel wall is peppered with tiny port holes in order to allow water to pass through it, but these tiny port holes act as a throttle controlled by the presence, or not, of the spear shaft sitting underneath them! The PПC-3 spear shaft diameter was 9 mm, which represents a cross-sectional area of 63.62 sq. mm. Each port hole in the inner barrel wall is 1 mm in diameter and the cross-sectional area of each one is therefore 0.785398 sq. mm. For the water flow rate through the port holes to match the incremental volume opening up behind the departing spear tail during the shot at least 81 holes must be able to flow water into the inner barrel because 81 x 0.785398 equals 63.62 sq. mm, i.e. the same cross-sectional area as the shaft. With the spear positioned under any given ring of port holes incompressible water cannot flow across into the inner barrel, hence only as the spear shaft advances out from underneath them does water flow from each ring of port holes into the opening "gap". Thus for a certain travel distance, represented by the linear spacing of rings which will contain the sum of 80 port holes, the gun is still being effectively choked until enough port holes are exposed that can then contribute to the required water flow, at which time the spear can accelerate with water now coursing into the inner barrel at the necessary replenishment rate as the spear's volume vacates that space. In the short production model this travel distance of 14.5 cm represents 36.3% of the total inner barrel length of 40 cm using a revised spacing* of the ports compared to that originally specified in the technical drawings. However in the longer prototype gun, if it was equipped with the more "compressed" port spacing used in the shorter production gun, then this restricted flow barrel length only represents 20.7% of the total 70 cm inner barrel length. Although the same hydraulic restriction is at work in the inner barrels of both versions of the PПC-3 gun, the prototype gun had a longer distance of barrel travel where full water flow was then operating and accelerating the spear shaft and that is why the longer gun was a much better performer than the shorter version.

Increasing the port hole diameter is an obvious solution to improving the water flow, but it comes at the expense of the durability of the surrounding rubber pipe which will gradually extrude down the holes when the gun is not being used. The 1 mm diameter port hole is more resistant to this happening and has been used in guns with rubber annular ring inlet valves to create the inlet port for the hand pump, in fact the PПC-3 speargun has such an inlet valve in the mid-body section of the gun. Even so PПC-3 owners were advised to depressurize their guns when not in regular use in order to remove this pressure created stress from the rubber pipe and avoid it being punctured with numerous tiny holes.

*Perhaps aware of the throttling limitation the designers of the production PПC-3 speargun increased the number of ports in a given ring of holes from 4 to 6 ports and also more closely grouped them together which effectively crammed the 80 holes into a much shorter length, but that was still not short enough to make the gun a better performer.
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Old 10-26-2016, 02:44 PM   #13
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Re: A Different Evolution

For those with a drill press, a supply of 1 mm diameter drill bits and a lot of time on their hands it may be possible to add another ring of 6 holes between each existing set which is rotated 30 degrees from the original port alignment. Thus the required 80 holes could be provided in about half the distance that they are now (actually 9.8 cm as there is a "lead in" section of plain tubing before the holes commence) and the performance of the production gun would be improved. Of course each drill press stroke produces two holes, as can be seen by the photo the holes wander around somewhat as the drill press operator lost concentration, hence care would be needed to ensure that holes do not "coincide" and end up making a larger hole. Too many holes will weaken the metal tube, which is why the inner barrel tube was not riddled with them in order to obtain the closest possible grouping of the ports.

I have now "added" holes to the previous photo to show what it would look like with an extra set of ports drilled between the existing rings of ports.
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Last edited by popgun pete; 10-28-2016 at 09:09 PM.
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Old 10-29-2016, 09:58 PM   #14
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Re: A Different Evolution

New diagram showing inner barrel port spacing options.
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Old 03-07-2017, 11:11 PM   #15
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Re: A Different Evolution

I had to produce this diagram for a Russian forum, but figured that it could go here as well. Imagine drilling all these (adjective deleted) tiny holes with nothing but a vee-block and a hand operated drill press and a jar of 1 mm diameter drill bits. This was the prototype gun that was said to be a satisfactory performer, but in the event the 70 cm barrel, 95 cm overall length gun was ditched for a shorter version which disappointed the users.

You could buy the much later realization of the concept manufactured in full titanium and created in a limited edition of 200 guns for a stratospheric price, but I don't know how many of those were sold.
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Last edited by popgun pete; 03-22-2017 at 08:28 PM. Reason: added second diagram
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