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.
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.
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