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Demka BR Series rubber powered pneumatic "look-a-like"

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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The skinny plastic trigger indicates that it is the later version with a cam lock trigger mechanism, similar to the one used in the Demka arbaletes. The rear grip handle is a glass reinforced plastic which was stronger than the plain black nylon version used in the first model which is the one shown in the cross-sectioned gun photo above. I guess that after all this time the tubular rubber power band has lost its stretch and has started to crack around the attachment to the metal tail. Demka made those tubular bands for some time after the BR guns ceased production, I remember seeing them as spare parts on their website, but that was also a long time ago.
 
Reactions: jorz21
Wow man that is awsome, really! I have never seen this gun before! I didn't realise demka was such an old firm! too bad they closed! damn depression! My father used to have a spring powered gun, greek make, too. I think he still has it! I will try to dig it up and show it to you!
 
Reactions: jorz21
Did you know Demka produced diving suits as well? A guy is giving away one on facebook! I had no idea!
 
I have added the instruction sheets to the original thread, but here is the English language version.
 
Reactions: Stamatis
What crippled these guns in Australia was zero marketing effort (from memory "Skindiving/Sportdiving in Australia" had but one half page advert with a polka dot bikini clad model holding a "Demka BR" gun) and no spare parts availability as the importer, "Indent Wholesale Sports Company", simply placed the guns with a random bunch of Sports and Fishing Tackle shops and with no selection of gun sizes in any particular shop. Thus each store, which I only found out by accident, had only the one "Demka BR" gun size on offer. Hence one shop may have had 100 cm guns, then another in a completely different location may have had 90 cm guns. Thus with no one knowing anything much about them, e.g. one guy in a sports store complained that there was no hand pump in the clear plastic gun packaging(!!), you can see why the guns were not a big success. I never got around to disassembling a rubber pipe to see how they were made as at one stage I contemplated making my own replacement bands.
 
It just occurred to me that the English language Instruction sheet must have been prepared for a Demka AR series gun which was more like these patent drawings, but by the time the guns made it to Australia they had progressed to the variable power Demka BR series guns with the sliding yellow plastic sleeve and circular barrel ports instead of the rectangular slotted barrel version.
 
More patent diagrams showing how the rubber pipe stretches and envelops the spear so that when cocked the spear is trapped in the gun.

only the legend here, which I added, should read Demka AR, not Demka BR!
 
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These patent drawings show the changes that created the variable power "Demka BR" series guns; the reduced volume for trapped water by adding an internal sleeve in the rear section of the outer barrel and the sliding plastic sleeve and circular ports which prevented water escaping and slowed the rubber pipe's ability to contract during the shot.
 
Very interesting. Come to think about it, back when I researched polespears for my own build, I came across some mentionings of roller spears. I think it might have been Phil Herranen who had tinkered with one where part of the band was inside the spear like in the Demka gun. If I recall correctly, which I may not be, his feeling was that he couldn't get enough power out of it because the water wouldn't let the band contract fast enough - and I guess there was a limit to how much you can weaken a polespear with flow openings. That's less of an issue in a gun, of course.
 
Here is a 1939 roller hand spear or pole spear, but the rubber is wrapped along the outside of the shaft as you can see from the patent diagram. Ventilating a tube to prevent water braking effects should not require too many holes, just think of a spring gun barrel and the ports they use.
 
Reactions: Diving Gecko
Thanks to Mel B who found this announcement by the importer back in December 1984.
.
 
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The later version of the “Demka BR” has a different trigger mechanism based on this Demka patent (see attached diagram). A cam lock, two-piece trigger mechanism replaces the previous tilting sear lever also used in pneumatic spearguns so that the mechanism is more secure against accidental discharge and wear effects that can occur with the “see-saw” type or “rocker” sear lever if they are not continually lubricated. Of course inside a pneumatic speargun this type of “rocker” sear lever is always covered in oil and never exposed to the environment which contains sand and other contaminants, but in the “Demka BR” gun it is and possibly foreseeing future problems in this regard the trigger mechanism was changed to one usually found in band guns. Note to make room for the new trigger mechanism the red safety slide switch had to be repositioned on the grip, formerly it was in front of the trigger then it moved to behind the trigger.
 
I recently “unpicked” the rollerspear patent diagram for another forum, but have decided to add it here as well.


Note that the spearfisherman releases the hand hook and keeps connected to the rollerspear by a tethering line connected to the hand hook which can just be seen at the rear end of the projectile. While swimming with the weapon cocked the small hook under the hand hook or grip can be temporarily snagged on the shoulder of the pole spear. 1939 vintage makes this a very early spearfishing weapon given that the first ever speargun patent is in 1937.
 
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I guess this is at least superficially like the Cressi rubber gun from the early 1950s? I realize that there are lots of differences but that Cressi was the only gun I ever saw that stretched a rubber tube inside the barrel. I never had one myself, but when I was a kid a diver just back from serving in the US Navy Underwater Demolition Team in the Korean war got my grandfather to take him out to the Tampa Bay ship channel markers to shoot Goliath Grouper and I went along. He brought a Champion Arbalete and that Cressi rubber gun. He would shoot a fish with one gun, get it up to there we could grab the gun and hand him the other one, then he'd go back down while we landed the fish. I don't recall seeing the rubber gun for sale, but later I did own the Cressi spring gun and the Arbalete. I think that trip is largely responsible for getting me into spearfishing.
 
The Cressi rubber gun is the "Mignon". I have one of those (photo attached), but the muzzle/head of the gun, which is blue rubber, has completely reverted. The gun was of a spring gun layout and had two rubber straps inside that connected in a tail fitting. Muzzle loading the gun stretched these bands out where they were then caught by the release mechanism which was activated by a connecting rod attached to the mid-handle trigger. The Demka used a rubber pipe that swallowed the spear, but the general principle is the same.
 
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One interesting aspect of the Cressi "Mignon" was that it had longitudinal slots rather than holes in the barrel tube and it was only much later did spring guns gain slots instead of being peppered with holes. Too many holes would weaken the barrel tube, not enough and a suction developing in the tube would affect travel of the fast moving shaft. It is interesting to note that the original layout for the Demka gun also had slots in the barrel tube as shown earlier.
 
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