First vacuum barrel gun?

[tromic]

I was curious about when was the first vacuum barrel gun invented. I had one vacuum barrel gun "Pilco mini" 40 cm long, about 40 years ago. I bought it in Zagreb in Croatia from a men who was producing and selling them. His name was Sraga Dragutin. I thougt he was the inventor but his son Rene told me, some day ago, that the inventor was engineer Josip Medud. After that I find this article:

Sommozzatore: Za?etnik podvodnog ribolova u Hrvatskoj, Josip Medur-Kit

"Već šezdesetih godina proizvode se u Centru za podvodna istraživanja u Rijeci četiri modela zračnih pušaka kojima ing. Medur potpisuje autorstvo. Te puške predstavljale su tada u svijetu tehnološko čudo."

First four types of pneumatic guns, the most advanced in the world in that time, were produced in Center for underwater research in Rijeka (City in former Yugoslavija - today Croatia) according to inventions of ing. Josip Medur. It was more than 50 yeas ago, in sixties.

It was the beginning of vacuum barrel pneumatic guns, maybe in the world! The fist mass production according to invention of ing. Medur was in Zagreb in 1963. (47 years before) in a workshop of Sraga Dragutin in Zagreb, Primorska 11. The workshop is still there. I will take a picture of some of the vacuum barrel guns from that time.

 

[tromic]

Here are few pictures of the pneumatic guns with vacuum barrel produced in Zagreb, Croatia by Sraga Drago and his son Rene. They had been producing from years 1963. to 1994. The sealing element were two O-rings joined together in the muzzle by rubber cylinder 4 mm thick. The barrel/piston was 13 mm and was using 8 mm shaft.

 

[popgun pete]

The first pneumo-vacuum speargun that I ever heard of was the "Korsar" (Corsair) from the Soviet Union, but I do not think it is 50 years old, it is a relatively modern development and has a quirky shape with no handle as such, just a horizontal grip. I have not found an early patent for the pneumo-vacuum idea either, so these Croatian spearguns could well be the first. Ideas can generally be tracked to series production guns as then there are references to them which can be dated, whereas home workshop inventors can make a single gun and then no one ever hears of it, unless they take out a patent or write up an article on the idea in a widely circulated magazine. I had thought that the vacuum barrel idea was not pursued until the quality of spear shaft surfaces became better in terms of long term durability. Chrome plated, zinc plated and cadmium plated shafts stay smooth for a while then develop small rust pits as the coating fails and begins to corrode itself. Scratches and microscopic flaws tend to breach the coatings exposing the metal underneath, so the process is accelerated with frequent use. Stainless steel shafts were usually made of 316 alloy which is very rust resistant, but can be easily bent, so tended to be optional fitment, plus they were more expensive. Spring steel spears usually rusted very quickly and had to be rubbed down periodically which does not provide an ideal surface in terms of "O" ring durability when such a spear is pushed through the seal in the muzzle, necessitating the changing of seals when they were no longer functioning properly. Freshwater diving, which is not such a corrosive environment, may have made the vacuum barrel idea a better proposition, but the mainstream manufacturers (France, Italy, Spain) were building products for use in the ocean. Today we have spring stainless steel, an ideal material for spear shafts, so the vacuum barrel gun is a much better proposition than it was in the past as muzzle seals will last much longer.

Perhaps you could check for a Croatian patent, there is a chance that one was registered, the problem is finding it!

 

[popgun pete]

I note that the guns in your photos have line slides and stops on the spear tails, so the muzzle seals are going to have to accommodate that change in diameter (bulge) as the spear tail passes through them. I guess that is why the muzzle seal is two "O" rings bridged by a rubber cylinder, this provides sequential sealing as when one ring is spread by the bulge on the shaft the other ring still seals on the shaft until it encounters the bulge and then the former ring seals on the shaft. That way the momentary loss of seal in one ring is theoretically negated by the second ring, but in practice I think that there would be a leak, however once the shaft bulge has passed through both rings then the vacuum condition in the inner barrel would hold. The main problem is how long do the seals retain their sealing action with repeated shots? Looking closely at the spear tails I see that the bulge is curved front and rear to ease its passage through the seals. This same curved shaft stop idea was used on the RPS-3 hydropneumatic which depended on muzzle sealing to retain hydrostatic pressure in the cocked gun, but the passage of the bulge through the muzzle made short work of the muzzle seals and each gun was supplied with 40 spare seals as a consequence! Another factor is that in order to preserve the smooth curved face of the stop or bulge on the shaft tail the stop ring has to closely match its contour or the stop ring will gradually hammer a sharp edge onto the face of the stop. Once that happens this sharp edge soon begins to damage the seals as the shaft travels through the muzzle on the way out of the gun. That is why the sealed slider became the first embodiment of the vacuum barrel in general use, it allowed the retention of a square edged stop on the shaft tail, although if the "O" ring holds up to being nipped in your latest "Tomba" we now know that the sealed slider can be reduced to a single "O" ring by placing the shaft centralizing washer (or stop ring) inside the muzzle rather than at the entrance.

 

[tromic]

I note that the guns in your photos have line slides and stops on the spear tails, so the muzzle seals are going to have to accommodate that change in diameter (bulge) as the spear tail passes through them. I guess that is why the muzzle seal is two "O" rings bridged by a rubber cylinder, this provides sequential sealing as when one ring is spread by the bulge on the shaft the other ring still seals on the shaft until it encounters the bulge and then the former ring seals on the shaft. That way the momentary loss of seal in one ring is theoretically negated by the second ring, but in practice I think that there would be a leak, however once the shaft bulge has passed through both rings then the vacuum condition in the inner barrel would hold. The main problem is how long do the seals retain their sealing action with repeated shots? Looking closely at the spear tails I see that the bulge is curved front and rear to ease its passage through the seals. This same curved shaft stop idea was used on the RPS-3 hydropneumatic which depended on muzzle sealing to retain hydrostatic pressure in the cocked gun, but the passage of the bulge through the muzzle made short work of the muzzle seals and each gun was supplied with 40 spare seals as a consequence! Another factor is that in order to preserve the smooth curved face of the stop or bulge on the shaft tail the stop ring has to closely match its contour or the stop ring will gradually hammer a sharp edge onto the face of the stop. Once that happens this sharp edge soon begins to damage the seals as the shaft travels through the muzzle on the way out of the gun. That is why the sealed slider became the first embodiment of the vacuum barrel in general use, it allowed the retention of a square edged stop on the shaft tail, although if the "O" ring holds up to being nipped in your latest "Tomba" we now know that the sealed slider can be reduced to a single "O" ring by placing the shaft centralizing washer (or stop ring) inside the muzzle rather than at the entrance.

Right, Peter! That is a god eye for technical details! This stop ring on the picture is made in brass not to damage the bulge on the shaft tail. I suppose that that brass ring should be changed often. But as I remember the gun I had 40 years ago had a steel sliding ring. I had no problem with damage of the sealing. Maybe I used some grease, I am not sure now, and I was not using the gun for more than 15 days during my holiday. In any case this gun could be used also with the free shaft. Somebody maybe think that somebody in Croatia was producing and selling a copy of Tovarich but you see the case is actually opposite. This system is known in Croatia for more than 50 years. Tomba is basically an implementation - copy of idea of this system as well as all other systems are: Mamba, Tovarich, X-power, Seatec Evo-Air, Calipso... The differences are mainly in shape of sealing element and some other details. There had been produced about 1500 guns of this type in different length. Some of them were water barrel but mainly vacuum barrel. There was only one thing I was not happy about them. I thought that the outside barrel should be larger. The compression ratio was too high and was difficult to finish loading the gun being on high pressure. Old Sraga Dragutin (the men who were producing guns) told me that he could not find out barrel with higher diameter. But the gun was very good. With 40 cm long gun I had, I could shoot a fish on 1,5 m with trident, with lighting speed even with a rope instead of mono line.

 

[popgun pete]

Tromic, perhaps you could tell us some more about these very interesting "Sraga-Sub" spearguns. The rear handle version appears to have a grip casting with a square edged buttress on the side which has a "P" shaped lever sitting on top of it. What does this lever do as it has a metal rod in the "eye" of the "P"? The mid-handle gun has a different shape for its casting, but has a similar feature where this "P" shaped lever is directly above the trigger in both examples. If the shorter gun is from 1963 then it is very early for a rear handle pneumatic speargun, it must be before the Mares "Sten" was produced. The smaller reservoir diameter and metal end sections would make this short gun a sinker, but it is a precursor of the most common form of pneumatic speargun today, I think that is very significant. Until you showed us these photos I had never heard of these guns.

What is the silver cylindrical object under the muzzle on the mid-handle speargun? It appears to be held onto the forward barrel with a metal clamp. The rear reservoir on the mid-handle speargun seems to be aligned above the inner barrel and the shaft length shows that it does not extend beyond the grip section. Going back to the rear handle model there appears to be another lever situated behind the trigger finger guard area, on the close up photo of the grip it is angled downwards, but on the full gun photo it is horizontal, perhaps this is a safety lever. The white plastic line slides look very much like those used by Mares, but maybe they are later additions. All the Mares line slides appear to be molded in black plastic, so I assume that these white line slides were independently manufactured.

Producing metal castings for spearguns that have a relatively limited production is very admirable, 1500 guns sounds like a lot until one thinks of guns that have been made in their thousands by the mainstream manufacturers over many years, sometimes decades, of production.

 

[tromic]

Tromic, perhaps you could tell us some more about these very interesting "Sraga-Sub" spearguns. The rear handle version appears to have a grip casting with a square edged buttress on the side which has a "P" shaped lever sitting on top of it. What does this lever do as it has a metal rod in the "eye" of the "P"? The mid-handle gun has a different shape for its casting, but has a similar feature where this "P" shaped lever is directly above the trigger in both examples. If the shorter gun is from 1963 then it is very early for a rear handle pneumatic speargun, it must be before the Mares "Sten" was produced. The smaller reservoir diameter and metal end sections would make this short gun a sinker, but it is a precursor of the most common form of pneumatic speargun today, I think that is very significant. Until you showed us these photos I had never heard of these guns.

What is the silver cylindrical object under the muzzle on the mid-handle speargun? It appears to be held onto the forward barrel with a metal clamp. The rear reservoir on the mid-handle speargun seems to be aligned above the inner barrel and the shaft length shows that it does not extend beyond the grip section. Going back to the rear handle model there appears to be another lever situated behind the trigger finger guard area, on the close up photo of the grip it is angled downwards, but on the full gun photo it is horizontal, perhaps this is a safety lever. The white plastic line slides look very much like those used by Mares, but maybe they are later additions. All the Mares line slides appear to be molded in black plastic, so I assume that these white line slides were independently manufactured.

Producing metal castings for spearguns that have a relatively limited production is very admirable, 1500 guns sounds like a lot until one thinks of guns that have been made in their thousands by the mainstream manufacturers over many years, sometimes decades, of production.

Peter, metal rod in the "eye" of the "P" - this is a trigger mechanism (lever). It locks the "mushroom" of the piston. In contact with the mushroom it has a shape like half of the circle.
The "eye" was sealed with two O-rings to the housing.

the silver cylindrical object under the muzzle - just a torch added. Not part of the gun.
To all other questions you already answered! All the parts except the barrels were produced in that small workshop in Zagreb. Some smaller parts are still producing for service, like pistons, shock absorbers, special sealing rings...
The rear reservoir on the mid-handle speargun is there, I suppose, to lower the compression ratio - to have more volume for air, but it makes the gun also more slim.
The valve for pumping the air was regular car valve. The first few guns had been made in 1960. Then production and selling started in 1963.
Cheers, Tomislav

 

[popgun pete]

Thanks for the answers, but perhaps I did not word my question about the rear reservoir on the mid-handle speargun properly. What I was wondering was whether the axis of the rear reservoir or tank was above that of the front barrel, your photo seems to indicate that. Usually the barrel on pneumatic spearguns is concentric with the tubular reservoir and they share the same axis. This is because the barrel continues right through to the rear wall of the reservoir in most pneumatic spearguns of this type and serves to hold the gun together. However one of the earliest pneumatic spearguns in 1946 was the "Sallematic" which was produced by Rene Salles in France. I think it was simply called the "Pneumatic". His gun had the mid-handle, rear reservoir layout, perhaps the first to do so, but most notably the central axis of the tubular rear tank was aligned above the barrel and was not concentric with it. There were two reasons for this unusual arrangement. One was the rear of the front barrel tube stopped inside the mid-handle and the rear reservoir contained a built-in air pump for pressurizing the gun which had a completely separate pumping tube. The second and most important reason was the trigger was of the "outrigger trigger" type as it projected out one side of the gun and descended on that side before being bent inwards and then downwards again to form a vertical hook for your finger to pull on the centerline of the gun. The trigger was effectively a single-piece mechanism operating a half circle cam incorporated in the trigger pivot rod passing transversely through the casting of the mid-handle. The cam acted directly on the mushroom tail of the piston via a cutout in the barrel hidden inside the casting. In order to improve the mechanical advantage by having a long trigger arm, Salles put the half circle cam on top of the barrel rather than underneath it, but to maintain a compact central housing in the vertical dimension he located the barrel at the bottom of the casting, not through the central axis of the grip section housing as we are more used to seeing it today. Consequently the cylindrical rear reservoir's longitudinal axis which connects behind the housing was out of alignment with the front barrel, being located above it. Rene's brother John later patented the "Salles" gun in the USA and said the front barrel having a lower alignment improved the resistance of the gun to muzzle flip as the reaction couple created by the axis misalignment between the barrel and the bulk of the rear reservoir (including the internal air pump) turned the muzzle down rather than up. Another interpretation is that the hand grip position was high up with respect to the barrel and provided a lower turning torque from recoil as the gun tries to pivot around the shooter's hand. Whatever the real advantage was it seemed that this design feature was not adopted by other guns.

However now that you have told us that the "P" is actually a side trigger that somehow links to the visible trigger inside the finger guard (there must be a slot somewhere to provide a link) it appears that the Croatian gun is a variation on the Salles gun, but with an improved appearance around the trigger area that looks much better than the bent rod trigger of the French gun. I do not know of any good photos of a Salles "Pneumatic" speargun, but there are photos of the "Airmatic" on the Web which is John Salles' American version of the gun which has a very similar appearance. The "Airmatic" was too expensive for the USA market which was dominated by the band gun by the time the "Airmatic" was released, so relatively few were produced, whereas many French "Sallematic" models were sold in Europe.

 

[popgun pete]

The Salles speargun that I described in my previous post is actually the version produced by John Salles, you can view the internal layout in his US patent 2,923,285 dated 2nd February 1960. It took a while to proceed through the US Patent Office as the patent was filed on 5th July 1955! Although there are a number of alternate speargun designs shown in the John Salles patent, the first version shown in figures 1, 2 & 3 on page 1 is the only one which was actually produced. Photos of the Rene Salles spearguns also show the forward barrel not quite in line with the rear reservoir tube, but his patent (France) 975.143 dated 11th October 1950 and published 1st March 1951 does not show that, instead everything lines up and appears to be concentric. The filing date is 8th June 1946, again a long time period elapsed between the lodgement or filing and actual granting of the patent. For those unfamiliar with such things the filing date is the priority date for an invention, that is the date from which ownership of the idea is awarded to the applicant, not when the patent was published.

In an illustrated advert for his Fusil "Pneumatique" spearguns Rene Salles refers to spearfishing patents 1946 - 1961 and international lodgements 1960 -1963, but as I have found no other patent by Rene Salles, in 1960 or after, I assume that he is including the patent held by brother John.

The 1946 French patent shows that not everything had been completely worked out, there are a couple of "outrigger trigger" designs (various transverse inclinations to the stock) including one showing a rear reaching finger or pawl engaging the piston's mushroom tail from the top, rather than the simpler (and perhaps later) half circle cam, plus a cable tether holding the piston in the gun, like a dog on a leash. There is a small diameter restriction indicated in the muzzle, possibly the uncoiling cable also stops the piston from blowing out of the gun at the end of piston travel by absorbing the impact! I am sure that this last idea was abandoned very quickly. I do not know when the first Salles model was actually produced, but it became the "Normal Series" (11 mm diameter harpoons) and was followed by the "Lightened Series" and "Light Series" (10 mm and 9 mm diameter harpoons) with a less bulky centre section for the mid-handle. A lot of the Salles guns held by speargun collectors today seem to be this lighter version, the original concept with the more bulky handle was to build a small torch into the lower section forward of the trigger as an aiming aid, the alloy casting under the barrel tube had a special extension to accommodate it. I have only seen one of these "Normal Series" guns, but I do not think it had a torch.

The sealing washers on the pistons were originally leather, so I doubt any thought was given to a dry barrel system in those very early days.

 

[tromic]

Thanks for the answers, but perhaps I did not word my question about the rear reservoir on the mid-handle speargun properly. Europe.
....

Very interesting Peter, as usual from you. Yes, you did word your question properly, but I don't know the answer. I should ask Sraga Rene, the son of Sraga Dragutin who made the gun. Maybe he could know the answer. These guns were not patented, neither the previous four designed by Josip Medur made between 1950. i 1960. I am trying to make a contact with a men who might have same of those first guns. I phoned a number from phonebook with his name but nobody answered yet.

 

[tromic]

Very interesting Peter, as usual from you. Yes, you did word your question properly, but I don't know the answer. I should ask Sraga Rene, the son of Sraga Dragutin who made the gun. Maybe he could know the answer. These guns were not patented, neither the previous four designed by Josip Medur made between 1950. i 1960. I am trying to make a contact with a men who might have same of those first guns. I phoned a number from phonebook with his name but nobody answered yet.

Sorry, but Rene is also not sure about the reason. But he told me that just the very first guns had such a construction. In later guns the thicker barrel (35 mm) was in line with the front barrel. He confirmed me what I said before that the reason for positioning the thicker barrel behind was to ease loading and better mobility of the gun.

 

[tromic]

I've got the drawing of one of the first Croatian vacuum barrel gun designed by engineer Josip Medur. This gun was from 1961. There were at least two guns before, in 1957. and 1959. The sealing in the muzzle was more rectangular in contact with the shaft. That was later changed by Sraga Dragutin to O-ring shape. It is obvious that Sraga was using this drawing for his guns making some minor changes.

 

[popgun pete]

These diagrams seem to take a long time to load, for some reason I can only see barely half of them.

Tried again and now I see everything, will add more comments later. Thanks for sharing this very interesting diagram.

 

[popgun pete]

This is obviously a working drawing for the pneumo-vacuum gun and reveals a number of things. The spear tail carries a hollow which the nose of the piston pushes into rather than the usual reversal of this arrangement. The piston carries the shock absorber on the exterior of the front section assuming that part 9 is a rubber sleeve. The trigger is of the "outrigger" type as it projects out one side of the gun. This design is used as it makes sealing of the penetration into the pressurized area of the gun relatively easy to accomplish with very few parts. In hindsight we know that it can be done in other ways, but that requires more elaborate designs to locate the seals and hold the various moving elements, especially if the trigger is remote from the sear, whereas here it is one combined element. Main difficulty is drilling the hole in the right place, it has to meet the inner barrel at a tangent to the top of the barrel. On the Salles guns the hole is drilled on a diameter of the gun body, so that is why the front barrel is mounted lower in the gun and not coaxial with the rest of the gun. It is much easier to drill on a diameter than on a chord if you drill a metal cylinder transversely.

The shaft tail butt is obviously designed to pass in a sequential sealing fashion through the double muzzle seal, the intra-seal gap is the size of the lip on the shaft tail. The real question would be how long the seals worked and uncertain gun performance if they leaked, you cannot really tell after the gun is cocked. A new gun or new seals should work OK for some time provided the user maintained some vigilance on the condition of the shaft tail after fishing in rocky areas and kept everything clean in the muzzle area. It is really surprising that if a reliable vacuum barrel system had been around in the sixties then why did such guns not become more widespread? I am sure that it was considered many times, but never pursued by the mainstream speargun makers as they would have to supply stainless steel shafts rather than the cheaper to produce items that came standard with most guns. Some were worse than others and all rusted sooner or later, some were junk when the companies tried to reduce costs in a lean period.

 

[tromic]

Peter, my first gun made by Sraga, that I bought 40 years ago, had very good stainless steel shaft. It had a boring to be attached to the piston, like on the last drawing, designed by Josip Medur. My gun was similar to that on the photo (the short one). Also the shaft to muzzle sealing was different - better (as I said before). The piston was made in aluminum. I can not remember if there were two O-rings on the piston or some other sealing combination but it was holding the air very good. The only thing I disliked was high compression ratio because the outer barrel was only 35 mm.

 

[popgun pete]

None of my Italian pneumatic spearguns ever had a stainless steel shaft and that included Mares, Cressi-Sub, GSD and Technisub. All shafts were cadmium plated steel (a dull gold colour) or some other coating in a silvery colour (Cressi-Sub). Very few guns had stainless steel shafts and these only arrived some time later as spare parts and that was for the Nemrod guns from Spain. The surface of the plated shafts began to deteriorate after one season, so were not really good enough for a vacuum barrel application if one had been available. I slowed the progress of the corrosion with a squirt of WD40 and let it run down the shaft when the shaft was propped up against a wall after a dive, but that was about it. When a shaft became too rusty I replaced it. At one stage the plating was so thin and uneven that new shafts rusted almost immediately, so you can appreciate why no one considered placing seals directly onto a surface that was eventually like fine sandpaper.

The large reservoir capacity guns (40 mm diameter) enabled low compression ratio, high average air pressure shooting, so there appeared to be no need for more efficient guns while divers were still prepared to turn themselves inside out while loading their longer pneumatic guns. Smaller reservoir guns are inherently less powerful as the average air pressure is lower (higher compression ratio), so they benefit from a vacuum barrel system as it makes the most of the gun's capabilities. The historical development seems to show pneumo-vacuum systems start with slim guns made by low production volume manufacturers who are prepared to increase the quality of components and are not trying to cut their production costs. This may change in future if the Chinese start reading these forums!

 

[tromic]

I find some pictures of the designer of the first pneumo-vacuum spearguns in Croatia, Josip Medur. He also had designed spring loaded guns in 1950. and band guns few years later. Pneumatic guns are from 1957. 1959. and 1961. All are exposed in the museum in Rijeka, Croatia.



This gun from 1961. was "KIT 61". This is the gun on the drawing few threads above.

 

[tromic]

This is a image of the actual speargun made by Josip Medur KIT-61
Those rifles represented a technological miracle in the world at that time. The first mass production of customized design, but based on the idea of a vacuum system by Josip Medur, was started by Dragutin Sraga, later his son Rene, in Zagreb, Croatia in 1963 until 1994.

 

[tromic]

An interesting fact is that one of the first, and perhaps the first speargun with compressed air is from Croatia. In the 1950s, at the center for underwater research in Rijeka, engineer Josip Medur constructed one of the first compressed air spearfishing gun, the Kit-57.

 

[popgun pete]

Interesting to compare the grip with the Rene Salles speargun. The rake of the alloy handle keeps it on your foot as you muzzle load the gun.