Here is a cautionary tale concerning playing around with pneumatic spearguns. I was experimenting with my "Cyrano 55" to see if one could make a "quick and dirty" vacuum barrel set-up. I wrapped the muzzle ports area with 3 cm wide "Cling Tape"; it is highly adhesive, has a cloth reinforcement with a soft vinyl coating and is often referred to as bookbinding tape (for repairing hardcover books with cracked spines). Two turns of the tape around the muzzle seemed to be enough to cover and seal off the relief ports. I placed a 6 mm inner diameter "O" ring on the shaft (I did not bother to check the ring's cross section) and then pushed it right down to the shaft tail stop diameter with the "Cyrano" stop ring and line slide sitting in front of it. Then I put the gun on my thigh, filled the muzzle to the brim with water from a cup to provide some lubrication and loaded the gun.
I then unscrewed the speartip and put the cocked gun with muzzle down into a full bucket of water to see if it would suck up any additional water, indicating that I had achieved a vacuum in the inner barrel, even if it was only a temporary one. Nothing seemed to be happening, so I removed the gun from the bucket, placed the threaded end of the spear on a big block of wood and pulled the trigger while leaning on the rear handle with my full weight. Just to take extra precautions I had the gun on the "low power" setting. The spear pushed the gun up as expected, but to my disappointment no water seemed to have been sucked up into the muzzle or the inner barrel. I then switched the gun to "full power" and sat the butt end in the bucket of water so that the gun was pointing slightly upwards at a nearby wall.
It usually takes some wiggling to get the jammed spear tail out of the socket in the piston face, so I turned around to find my sliding hammer device when I heard a loud bang followed by the clang of the spear landing back near the bucket after ricocheting off the wall. This was a very big surprise to me until I figured out exactly what had happened!
The gun had developed an inner barrel vacuum initially, but it had then sucked the "O" ring through the muzzle diameter restriction and the bore of the shock absorber anvil sitting directly behind it. What I did not realize was that when I control fired the gun against the block of wood the spear had only emerged as far as the shaft tail stop diameter encountering the rear face of the shock absorber anvil and the "O" ring abutting the radial step on the shaft was stopping it coming right through. I calculate that it had another 2.4 cm of travel left. Switching the gun to "full power" added that bit more air pressure and the "O" ring not long after busted in two allowing the shaft to complete its exit from the gun when I had no control over it.
I should have used a fatter cross section "O" ring, it was just one out of a box of spare rings that I had. If I had removed the tape around the muzzle earlier then I would have seen the shaft body through the relief ports instead of the white nylon of the piston body and would have realized exactly what had happened, but I had been distracted by the "O" ring failing to emerge from the muzzle. Unknown to me it was actually waiting to complete its new job as delayed action trigger! Even with all my experience it nearly caught me out, so watch out when parts seem to disappear for no apparent reason, that shaft could have taken an eye out if pointed in the wrong direction.
I then unscrewed the speartip and put the cocked gun with muzzle down into a full bucket of water to see if it would suck up any additional water, indicating that I had achieved a vacuum in the inner barrel, even if it was only a temporary one. Nothing seemed to be happening, so I removed the gun from the bucket, placed the threaded end of the spear on a big block of wood and pulled the trigger while leaning on the rear handle with my full weight. Just to take extra precautions I had the gun on the "low power" setting. The spear pushed the gun up as expected, but to my disappointment no water seemed to have been sucked up into the muzzle or the inner barrel. I then switched the gun to "full power" and sat the butt end in the bucket of water so that the gun was pointing slightly upwards at a nearby wall.
It usually takes some wiggling to get the jammed spear tail out of the socket in the piston face, so I turned around to find my sliding hammer device when I heard a loud bang followed by the clang of the spear landing back near the bucket after ricocheting off the wall. This was a very big surprise to me until I figured out exactly what had happened!
The gun had developed an inner barrel vacuum initially, but it had then sucked the "O" ring through the muzzle diameter restriction and the bore of the shock absorber anvil sitting directly behind it. What I did not realize was that when I control fired the gun against the block of wood the spear had only emerged as far as the shaft tail stop diameter encountering the rear face of the shock absorber anvil and the "O" ring abutting the radial step on the shaft was stopping it coming right through. I calculate that it had another 2.4 cm of travel left. Switching the gun to "full power" added that bit more air pressure and the "O" ring not long after busted in two allowing the shaft to complete its exit from the gun when I had no control over it.
I should have used a fatter cross section "O" ring, it was just one out of a box of spare rings that I had. If I had removed the tape around the muzzle earlier then I would have seen the shaft body through the relief ports instead of the white nylon of the piston body and would have realized exactly what had happened, but I had been distracted by the "O" ring failing to emerge from the muzzle. Unknown to me it was actually waiting to complete its new job as delayed action trigger! Even with all my experience it nearly caught me out, so watch out when parts seem to disappear for no apparent reason, that shaft could have taken an eye out if pointed in the wrong direction.
