back some 50 years ago

[Scuba Lawyer]

@Scuba LawyerI have all 4 guns in my dive locker-- next visit well get them out and air fire

Cool!

Sam, you gots the neatest toys of any kid on the block! M

 

[Popgun Pete]

I wonder if there would be an opportunity for a hybrid system that still used a closed captive piston like a conventional modern pneumatic gun, but each shot was powered by a CO2 cylinder?
Manual vent valve to allow the spear and piston to return easily down the unpressurised barrel for the next shot... vs quite difficult in a regular pneumatic of any length.
Sealing the trigger mechanism against ~900psi CO2 and still have an acceptable trigger release could be an issue though, even with a 1.5mm pin!

It certainly has been thought of and you could pressurize a pneumatic gun with a carbon dioxide cartridge, in fact it has already been done with pistonless pneumatic guns. These use high gas pressure as the spear is both inner barrel and piston in essence with the spear moving through a fixed seal in the muzzle. The spear diameter at say 8 mm is a lot less than the 13 mm diameter for a standard pneumatic gun piston. Which is about 0.4 or 40% as (8/13) squared is 0.3787. To compensate for the small cross-section that the internal gas pressure acts against the internal pressure is boosted compared to the usual pneumatic gun pressure of 400 psi.

A long standing form of pistonless gun is the "Vlanik" and here you can see one with its carbon dioxide fill device that injects gas through the muzzle.

Since this gun was made they have slimmed down a lot and been made much lighter, for example the latest variation is this "Mavka" pistonless gun, but they are unavailable in the West.

The later guns are pumped up with air, but it takes a narrow bore pump to push air in past 600 psi and if you want to reach 900 psi then it is much easier to use carbon dioxide gas.

 

[Popgun Pete]

Here is an annotated photo of the earlier "Vlanik 48" gun, the parts are more refined these days, but everything works in exactly the same way even today.

These guns date back 40 years in Russia and came to prominence when the inventor used this type of pistonless gun to win a Championship in speargun competition shooting. The guns are very efficient as they only have one seal, but can lose gas through the muzzle and let tiny amounts of water into the gun with each shot via the join in the spear tail cap. If the spear tail cap, which acts as a plug, falls off inside the gun then all the gas escapes from the gun with the next shot!

 

[Fibonacci]

Interesting!
Thanks for the detailed update...
Though I wonder what the advantage if having a piston-less design would be vs a CO2 powered captive piston?
Less friction for sure but as you point out that is then offset by ~40% less surface area and a more fragile design with the tail cap canting or becoming dislodged inside the gun.
I imagine even small scratches on the spear shaft or minor bends would play havoc with the muzzle seal!

 

[Popgun Pete]

Interesting!
Thanks for the detailed update...
Though I wonder what the advantage if having a piston-less design would be vs a CO2 powered captive piston?
Less friction for sure but as you point out that is then offset by ~40% less surface area and a more fragile design with the tail cap canting or becoming dislodged inside the gun.
I imagine even small scratches on the spear shaft of minor bends would play havoc with the muzzle seal!

Apparently the spears used are pretty hard stuff and don't scratch up very easily, so for the conditions in which they are used such as rivers and lakes with a lot of suspended silt in the water the pistonless guns have a long service life. How they would fare in marine use with quartz grit type sands is an unknown, and where I dive there is plenty of the latter. The problem with a captive piston with 900 psi acting behind it is decelerating the piston at the muzzle and the current crop of plastic pistons would most likely be cracked on impact. Metal pistons may survive, but the muzzle shock absorber would need to be very different to what is used now. It is not impossible as a Greek guy had a fiber wrapped tank for strength on a highly modified pneumatic that was charged up to ultra-high pressure, but it required a winching system on his boat to cock it! Any system that lets gas out of the gun with each shot will be banned as the rules are very strict on expellable gas.

 

[BRT]

It certainly has been thought of and you could pressurize a pneumatic gun with a carbon dioxide cartridge, in fact it has already been done with pistonless pneumatic guns. These use high gas pressure as the spear is both inner barrel and piston in essence with the spear moving through a fixed seal in the muzzle. The spear diameter at say 8 mm is a lot less than the 13 mm diameter for a standard pneumatic gun piston. Which is about 0.4 or 40% as (8/13) squared is 0.3787. To compensate for the small cross-section that the internal gas pressure acts against the internal pressure is boosted compared to the usual pneumatic gun pressure of 400 psi.

A long standing form of pistonless gun is the "Vlanik" and here you can see one with its carbon dioxide fill device that injects gas through the muzzle.
View attachment 517029
Since this gun was made they have slimmed down a lot and been made much lighter, for example the latest variation is this "Mavka" pistonless gun, but they are unavailable in the West.
View attachment 517031
View attachment 517032
The later guns are pumped up with air, but it takes a narrow bore pump to push air in past 600 psi and if you want to reach 900 psi then it is much easier to use carbon dioxide gas.

You will have to be diving in warm water to get CO2 to 900 psi.

 

[Popgun Pete]

Well the chamber pressure will be more than enough as carbon dioxide guns were used extensively in the fifties. For the actual gas pressures if people are interested then they can read this https://www.linde-gas.pt/en/images/Safety_Advice_12_tcm303-25938.pdf

 

[Popgun Pete]

Here is a pistol version of the Pelletier selling on eBay. This small gun uses the sparklet cartridges for each shot.
VINTAGE SPEARGUN CO2 PELLETIER P2 Short sparklet system | eBay