What is commonly referred to as the Heinrich line release system (Heinrich must be the man who first implemented it) is a very simple and efficient way of rigging a line release on a speargun. It's really a wonder that more spearguns don't use this system, as any other kind of auto resetting line release complicates the build. IMO installing a Riffe style line release is the most difficult part of the build, or the part where a mistake can most easily be made. A good auto resetting line release is also missing in most euro/pipe guns with integrated handle/mech. But you can't use a Heinrich system on Euro shafts that don't have tabs for anchoring bands.
The way the Heinrich works is by routing the shooting line once on each side of the gun and catching it on a shaft tab. This is more easily seen in a picture than described. When the shaft starts moving forward the loops come off the tab and the shooting line becomes free. It is a fool proof system of which the only disadvantage is that the shooting line runs on each side and this may affect the comfort of carrying the gun by gripping the stock?? You can actually route the line with both wraps on one side but this tends to twist the shaft towards one side. If you have an enclosed track this twisting effect is minimized.
Some examples with wood spearguns: