Демка BR руёье

[νικηφ]

How do these guns shoot?
Shafts seem quite thick

[popgun pete]

Melbourne, Australia which is said to be the third largest Greek city in the World.

[popgun pete]

How do these guns shoot?
Shafts seem quite thick

The smaller one shot about the same as a pneumatic gun of a similar size. It did not float after the shot as a pneumatic gun usually does. The power reducer sleeve easily jammed on the barrel if any sand got into it and freeing it damaged the anodized coating, so I completely removed it. As all loading effort is expended every time you pull the trigger I used full power. I don’t know how much the performance would suffer as the rubber band began to weaken. I put the gun aside as there were no replacements available and I decided to keep the gun intact rather than wear it out. The larger gun I purchased when a pile of them were disposed of to get rid of them, the rubber parts had stiffened as they had not been stored properly.

[miker]

this spearguns were available in Australia?

[popgun pete]

this spearguns were available in Australia?

Yes they were imported here from the very beginning and advertised in our local spearfishing magazine. I attach the two sided instruction sheet in English which was included with each gun as well as the original version in Greek which I have shown here earlier.

[popgun pete]

The Demka BR spearguns were first discussed here. https://forums.deeperblue.com/threads/d ... uns.89582/
and here https://forums.deeperblue.com/threads/d ... ost-972128

[miker]

demka was a very good company! I stiil use the classic amiII speargun!

[νικηφ]

So Pete when loading this gun you 'd place the shaft inside the rubber band?

How does closing the barrel holes affect the power of the gun?
Is there any vacuum effect forming?

[popgun pete]

So Pete when loading this gun you 'd place the shaft inside the rubber band?

How does closing the barrel holes affect the power of the gun?
Is there any vacuum effect forming?

Yes, you insert the spear into the hole in the tubular rubber band and as shown in the diagrams the rubber tube stretches and narrows so that the thinner rubber tube formed by stretching tightly holds the spear and prevents it from falling out of the gun. When the gun shoots the rubber tube shortens and expands, but to do so water inside the metal barrel tube at the front end is displaced. If you close the holes in the side of the metal barrel tube then water can only get out through very small gaps and this has the effect of reducing the power of the shot. The rear end of the barrel tube has an inner sleeve to minimize volume there in order to prevent trapped water from moving rearwards.

[νικηφ]

Thank you Pete!
What a great idea! Was this mechanism exclusively used by Demka ?

Wondering about range and recoil..

[popgun pete]

Thank you Pete!
What a great idea! Was this mechanism exclusively used by Demka ?

Wondering about range and recoil..

Yes I think so. There was a patent for a speargun that had a loading winch arrangement at the rear end that pulled a rubber band back that was used to propel a spear from a similar pneumatic appearance gun, but I have never seen one. Many patents do not eventuate in a product. The “Demka BR” speargun possess a very attractive appearance, whenever I used the gun it created a lot of curiosity from other divers who were intrigued by its operating system. If supplies of replacement tubular bands had been readily available then the gun would have been more successful here. Recoil is low as the gun is filled with water which increases its inertial mass. The gun traverses easily as there ae no exposed bands to vibrate with hydrodynamic drag as is the case with normal band guns. In my view the “Demka BR” gun should still be in production as there will be a market niche for it with divers who want a simple gun which is reliable add suffers no air leaks.

[popgun pete]

Some typos which I have corrected:

Yes I think so. There was a patent for a speargun that had a loading winch arrangement at the rear end that pulled a rubber band back that was used to propel a spear from a similar pneumatic appearance gun, but I have never seen one. Many patents do not eventuate in a product. The “Demka BR” speargun possesses a very attractive appearance, whenever I used the gun it created a lot of curiosity from other divers who were intrigued by its operating system. If supplies of replacement tubular bands had been readily available then the gun would have been more successful here. Recoil is low as the gun is filled with water which increases its inertial mass. The gun traverses easily as there are no exposed bands to vibrate with hydrodynamic drag as is the case with normal band guns. In my view the “Demka BR” gun should still be in production as there will be a market niche for it with divers who want a simple gun which is reliable and suffers no air leaks.

No mention of the BR series guns here in 2004 https://opensea.ru/documents/Instr_DEMK ... gunsEN.pdf

[popgun pete]

Here are the drawings from the Greek patents that describe the functional elements of the “Demka BR” series spearguns. Note that there are some differences in layout which made me wonder if initially there was an earlier “Demka AR” series.

[popgun pete]

Here are the drawings from the Greek patents that describe the rubber pipe used for storing loading effort energy in the “Demka BR” series spearguns. Note again that there are some differences in layout which made me wonder if initially there was an earlier “Demka AR” series.

[popgun pete]

The “Demka BR” series speargun which was released in the mid-eighties in Australia. Stores had different versions, the first guns that I saw were “BR 100” models in a sports store in Coffs Harbour which is a well-known spearfishing location. Next guns were the small “BR 60” models in my local shopping area. Then after many years the “BR 90” models were seen at Narooma, another well known fishing location and this is where I purchased that gun and in later years an extra rubber pipe which unfortunately had become stiff as the rubber dried out. I always intended cutting one up to determine the method of construction to see if I could make one using surgical rubber, but ¾ inch diameter was about as thick as could be found and the hole in the centre needs to be able to swallow the spear of 8 mm diameter.