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

popgun pete

Well-Known Member
Jul 30, 2008
2,424
432
123
Australia
#1
You would be forgiven for thinking that this speargun was a pneumatic if you saw one for the very first time, however it is not. More info can be seen here as I just found the Greek patents that gave rise to this attractive looking gun and launched it onto the world spearfishing market in the mid-eigthies.
https://forums.deeperblue.com/threads/demka-br-series-elastic-spearguns.89582/
Demka BR cutaway.jpg
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,424
432
123
Australia
#4
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.
 
Likes: jorz21

Stamatis

Active Member
Aug 29, 2017
105
33
43
43
Athens
#5
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!
 
Likes: jorz21
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,424
432
123
Australia
#8
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.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,424
432
123
Australia
#9
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.
Demka rubber powered pneumatic style gun R.jpg
Demka rubber pipe R.jpg
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,424
432
123
Australia
#10
More patent diagrams showing how the rubber pipe stretches and envelops the spear so that when cocked the spear is trapped in the gun.
Demka 2.jpg

only the legend here, which I added, should read Demka AR, not Demka BR!
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,424
432
123
Australia
#11
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.
Demka 3.jpg
Demka 1.jpg
 

Diving Gecko

Well-Known Member
Jun 24, 2008
1,121
271
138
Shanghai
#12
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.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,424
432
123
Australia
#13
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.
roller handspear.jpg
 
Likes: Diving Gecko
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
2,424
432
123
Australia
#15
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.
Demka new trigger.jpg
Demka early handle.jpg
Demka later handle.jpg