Demka BR series elastic spearguns

[popgun pete]

I posted the SOS "Ringo Hydromatic" in the pneumatic spearguns section as I had thought it may have been a hydropneumatic speargun, however is not the only elastic powered gun that could be mistaken for a pneumatic model. Another speargun which superficially looked like a pneumatic speargun was the Greek Demka BR series elastic powered speargun. The Demka BR speargun uses a concentric rubber pipe mounted inside the large diameter aluminium body tube which is stretched by the diver's muzzle loading effort on the spear shaft tip. As the rubber pipe stretches it reduces in diameter, thus retaining the spear inside the gun once it is fully cocked as the rubber pipe then wraps firmly around the shaft tail and holds it in place. In a sense the elongated rubber pipe replaces the inner barrel tube which you would normally expect to find in a speargun of this appearance. The rubber pipe anchors at the black plastic muzzle moulding and has a metal tail piece with a mushroom head similar to that used on a pneumatic speargun's piston. The "see-saw" type sear lever that engages this mushroom head in the early Demka BR models is similar to the one in a Mares "Sten" pneumatic, but later on it was replaced by a two-piece cam lock mechanism as used in many band guns (e.g. Undersee, Riffe, etc.). To incorporate the new trigger mechanism the rear grip moulding was modified by changing the pivot pins and locating pins for the revised trigger parts and a larger access slot in the lower trigger figure guard was provided for their installation. While a pneumatic type trigger mechanism works fine inside the fully protected and lubricated interior of a pneumatic speargun, it will be affected by grit and increased tooth wear when directly exposed to the marine environment. Replacing the flooded trigger mechanism with one that cam locks, rather than being a simple hook which is what the "see-saw" type sear lever is, no doubt improved the reliability of the cocking action, something you need in a muzzle loader! The Demka BR guns do not float after spear discharge as water floods the entire length of the gun.

The attached photos show both versions, the BR60 is the earlier version (note the fat trigger) and the BR90 is the later version with a much smaller trigger and a relocated safety position behind the trigger instead of in front of it. Although the operating principle is simple the gun has more internal parts than you would expect. There is a small coil spring on the rubber pipe tail section to prevent over-pushing of the metal mushroom head into the sear box during muzzle loading. The interior of the barrel reduces in diameter about half way down the gun using an internal sleeve to better direct the stretched rubber pipe and ensure that the pipe's metal tail goes directly into the sear box when the spear is fully pushed into the gun.

The yellow plastic sleeve slides forwards to cover the side ports in the front of the barrel to impede water escaping from the interior of the gun as the internal rubber pipe returns to its original size during the shot. That reduces the power of the shot, according to the instructions. I only tried it once before taking the sleeve off as sand easily got caught between it and the barrel tube and would soon make short work of the anodized surface by scratching it.

 

[foxfish]

That is amazing Pete!
I have often wonders if this would be possible to build but, i should of guessed someone already had.
Thanks for your post...

 

[popgun pete]

Someone told me that there was a gun called the "Triton" that used a similar system, but I have never found any other reference to it. Demka have a number of patents on the designs used in their BR series gun, however the patents (which I have viewed) appear to be for Greece only as I have not found any international patents taken out by that company for this speargun. Even when released here in the mid-eighties potential purchasers were concerned about the availability of replacement rubber pipes. The guns were not widely sold here, I found the BR60 in a local sports store after first seeing BR100 models in a fishing tackle shop while on vacation in Coffs Harbour. The side ports were poorly machined in those longer guns as the drill bit had chattered on the tube surface creating a multi-scalloped edge to each hole. I figured that there would be better examples if I waited, but the next gun I saw was the BR60 which did have properly drilled holes. It took me a year to decide to purchase it, the shop only had two of them and they were both still there a year later, no one was in a hurry to buy one! Very similar performance to a small pneumatic, I shot a few fish with it, but found no real advantage in using it and being a sinker in my view negated one of the most convenient aspects of this gun format. The BR90 was found over a decade later in a coastal town (Narooma) sports store, the shop had purchased a job lot of them as old stock, the polyethylene packaging bags were covered in grime and by then the rubber pipes had lost some of their stretch and were nearly impossible to load. I could see that there was something different about the handle, the guns were cheap, so I bought one to compare with the earlier gun back home. That shop had those guns for a number of years, I saw them each time I passed through there on my annual spearfishing trips up north. By then they would have been curiosity value only.

 

[popgun pete]

Here are the rubber pipes which have been stored in plastic bags in an attempt to preserve them. The OD of each rubber pipe is 26 mm (1") and the ID is 9 mm, although a replacement pipe I found some years later has a larger ID at about 17 mm when measured at the front end. The spear shaft diameter is 8 mm and the stop diameter on the shaft tail is 9 mm. The white nylon or acetyl plastic collar at the front end of the rubber pipe simply slides into the black plastic bulkhead and is held in place there by the screw threaded muzzle nose cone. The metal tail piece is affixed in a slightly different fashion in the later rubber pipes, in the side-by-side comparison the earlier version is shown on top and is the pipe from the BR60. The black band seen between the white plastic tail sections on this pipe is ground down rubber. The sprung loaded plastic locating sleeve for alignment into the "sear box" tube can be seen on the tails just in front of the metal mushroom head, the coil spring provides some additional resistance as the mechanism latches and along with the click as the sear tooth engages on the mushroom head indicates that you can stop pushing on the shaft.

When the gun is cocked to shoot the rubber pipe has to be stretched to about 3 times its free length. At 1" diameter these "bands" are relatively thick, but then you only have to stretch one strand, not two as you do with a normal band gun.

Inventor is Nikolaos Katapotis, this Demka gun dates from 1982 when the first patent was applied for in Greece. The form shown here dates from 1984 when the power regulator sleeve was patented, including the multiple side ports at the front end and stepped internal diameter of the body tube that go with it. The revised trigger mechanism version with the glass reinforced nylon handle appears to date from 1987 when the same trigger mechanism was to be used in a conventional band gun also manufactured by Demka, that is when patents were taken out for the new trigger mechanism and a wishbone band ferrule system.

 

[popgun pete]

A few more photos showing the rear port in the grip handle, which allows water to flow in and out of the gun during stretching and contraction of the rubber pipe, and additional views of the muzzle end of the gun.

 

[popgun pete]

I found some of the patent drawings that show the "Demka BR" guns in a slightly different form in terms of the muzzle nose cone attachment, but otherwise everything else in the same. Note the inner tubing inside the outer barrel/body tube which is placed there in order to guide the rubber power band as it is being stretched back inside the gun during muzzle loading. The forward mounting point for this inner metal tubing is indexed into the outer body tube by a silvery finish plastic "button", which is part of an internal plastic collar, that can be just seen projecting outwards, but sitting flush with the outer tube at approximately mid-length on the guns' outer tubing.

 

[popgun pete]

Here is how the guns were envisaged in the first 1982 Greek patent. Note the ventilated barrel/outer body tube with elongated port holes and a much simpler internal construction.

It is possible that there was an earlier "AR" series of this "Demka" speargun which may only have been sold in Greece, but I have not seen any photos of it. If there was then it would most likely have been exactly as shown in these initial patent diagrams.

 

[popgun pete]

And a cut-away diagram showing the "Demka BR" Speargun as initially produced with the "rocker" type sear lever which was "borrowed" from that used in most of the then contemporary pneumatic powered spearguns. Later on it was equipped with a two-piece, "cam lock" trigger mechanism.

 

[popgun pete]

I recently scanned the instruction sheets both in English and Greek, so decided to add them here.

 

[popgun pete]

And here is the Greek version.

 

[popgun pete]

Here is a detail from the sectioned speargun photo. The rocking sear lever can be easily seen, note that there is no trigger transmission pin, instead there is a raised section on the upper rear of the plastic trigger.

 

[popgun pete]

A notice from the importer in December 1984 about the then new "Demka" guns from Greece.

 

[Stamatis]

I wonder how it performed in terms of power. The obvious advantage is the lack of oscillation and recoil. It's an interesting solution.

 

[popgun pete]

The guns shot much like a pneumatic, but the performance was down compared with a pneumatic gun of the same length as the working course of the piston, in this case the metal tail released by the trigger, was less as the rubber pipe free length meant the spear was not being propelled right up to the muzzle as it is in a pneumatic gun. The shot was relatively quiet as no piston was hitting the usual muzzle anvil, but from memory it was not completely noiseless. The clean lines of the gun gave it an easy traverse in the water. As rubber is not as efficient a spring the pneumatic will always have an edge, but surprisingly the rubber pipe guns performed well. As the rubber pipe aged the longer guns became hard to load, but more modern rubber formulations would have improved this aspect.