Pneumatic spearguns from the beginning used a coil spring as a shock absorber in the line slide assembly on their spear shafts once they quit using front tied spears. That was almost universal until Mares introduced their first Cyrano which was a gun dedicated to shooting 7 mm shafts. Mares introduced a new hydrodynamic plastic line slide backed by the usual metal stop ring or thick washer, but the intervening coil spring was gone. Instead they tied a rubber ring like a big "O" ring into a line loop in the line end connected to the muzzle which acted as a shock absorber to protect the shooting line from strong jerks, plus it also had the advantage of tensioning the shooting line when the line wraps were wound on the gun’s line hooks.
What they had forgotten was the shock absorbing coil spring also protected the line slide from shocks, particularly shocks that had the potential to crack the plastic versions. The purpose of the metal stop ring is to spread the impact over as wide an area as possible on the back of the line slide and this was also achieved with the coil spring by pinching the last coil at each end and grinding the spring ends flat so that the line slide sat on an almost complete metal ring. The omission of this coil spring meant that plastic line slides were then being hammered as the spear collected them on the way out the muzzle. This effect was exacerbated when plastic line slides appeared with crosscut slotted backs to weaken them further in the interests of running mono shooting line close to the shaft as the shaft flies through the water. Metal line slides have been used instead, but to keep their weight down they are rarely symmetrical and drag the shaft from one side. Ideally the shooting line should be pulled in the shaft's wake running coaxial to the shaft and this was usually accomplished by line running from either side of the line slide in a short loop that connected to the shooting line, the loop being just long enough to extend past the shaft’s tail end.
The old-style plastic line slides were more robust than the current crop which in seeking streamlining have become too weak, plus depressingly many seemed designed only for mono. You can still buy the older designs from suppliers like Salvimar who also make parts for many other brands.
What they had forgotten was the shock absorbing coil spring also protected the line slide from shocks, particularly shocks that had the potential to crack the plastic versions. The purpose of the metal stop ring is to spread the impact over as wide an area as possible on the back of the line slide and this was also achieved with the coil spring by pinching the last coil at each end and grinding the spring ends flat so that the line slide sat on an almost complete metal ring. The omission of this coil spring meant that plastic line slides were then being hammered as the spear collected them on the way out the muzzle. This effect was exacerbated when plastic line slides appeared with crosscut slotted backs to weaken them further in the interests of running mono shooting line close to the shaft as the shaft flies through the water. Metal line slides have been used instead, but to keep their weight down they are rarely symmetrical and drag the shaft from one side. Ideally the shooting line should be pulled in the shaft's wake running coaxial to the shaft and this was usually accomplished by line running from either side of the line slide in a short loop that connected to the shooting line, the loop being just long enough to extend past the shaft’s tail end.
The old-style plastic line slides were more robust than the current crop which in seeking streamlining have become too weak, plus depressingly many seemed designed only for mono. You can still buy the older designs from suppliers like Salvimar who also make parts for many other brands.
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