Here are some answers to the questions :
The concept of this super-pneu from my friend is basically the same as what I have always wanted in a gun. Short, no longer than 110cm, powerful like a Blue Water gun that can shoot at least 8 meters deadly. Recoiless or at least low recoil. Mid handle design for easy swing. Trigger quality like Riffe or Alexander or at least close to it. Lightweight, in proportion to its power output. Accurate. Unfortunately pneumatic can not be made quiet like band guns with open muzzle and no slide ring.
01. FIRING CHAMBER/BARREL MUST BE DRY
In a normal pneu, you cock the piston to lock in the trigger by pushing in the shaft. The shaft sits on the piston, push the piston
down all the way in till it get engaged on the trigger sear. Water will enter the barrel/chamber into whatever gap there is between barrel diameter and shaft diameter. An o-ring at the shaft front will be useless at this stage because water is already in. Unless you want to remove the shaft (hopefully not getting killed in the process ), fill air in the barrel/chamber by lifting the gun out of the water or by using a small straw or hose while keeping the gun inverted. When air has filled up the entire barrel/chamber, load the shaft back in and that o-ring will keep the air in. One problem. This kind of pneu will not allow the use of slide ring for the shooting line because if an air tight seal is to be provided at the front part of the shaft, it means the diameter of that particular air tight area of the shaft will be bigger than the diameter of the butt of the shaft which normaly has the cone adaptor that allows the shaft to sit tight on the piston.
So, the shooting line attachment can not use the normal slide ring or be positioned at the back of the shaft. It must be attached at the forward part of the shaft. Accuracy effected ? Must experiment in depth.
Let's say we fill up the barrel with air at surface level which is 1 ATM, we dive down to 90 feet, the o-ring on the shaft must be good enough to withstand at least up to 150 feet or 5 ATM of pressure, not a difficult task. If a scubadiver owns this gun and fill the barrel at 90 feet and he later go shallow at 30 feet, the air in that barrel will expand and might push the shaft out of the gun. Thus the design of the o-ring on the shaft must also withstand that air expansion. This is why my friend wanted me to test for him because he is not a scubadiver. I wanted to bring down the gun to 140 feet and see how the o-ring seal work. I will also need to fill up the barrel with air at 140 feet and later surface, to see if the shaft gets pop out of its piston seat due to air expansion. I never could find the time to do this tests.
It seems the design will be better for a freediver who does all loading/cocking on the surface at 1 ATM.
02. SUPER POWER
Any pneu that can be loaded the way a normal pneu is loaded, by pushing the shaft in and cock the piston, can never be super powerful. The limit of the power is then limited to the single cocking capability of the hunter. What make band gun so powerful is that the total accumulation of so many powerbands can be cocked one by one. If say a Blue Water Gun using 4 x 5/8 bands is to be designed with a single band of 64mm, no one could ever load the gun. This is the dead end for pneu designer. Want more power......?....easy to make on the engineering side but how would one load the gun ?? Cobra of Brazil use a special dummy shaft to load their powerful model, something like that. But how much force can be applied to load that shaft without having to bring say a car jack ? The limitation will also be on the shaft that load the gun. There is a limit on how much force can be applied to a pneu using its own shaft before actually bending the shaft itself during the cocking stage. With the available free play between shaft diameter and piston diameter, the shaft have room to flex.
Now assuming I have a super pneu with a piston diameter that qualifies to be 1 inch square. I pump/charged the gun to 25ATM or 375PSI. I will need to overcome a force of 375 pounds to drive the piston down with the shaft, plus friction and add the increased pressure as the barrel area become smaller and air get compressed even higher. How the hell do I push a shaft in with such tremendous power ?? Bring my neighbours ?? Here is where every pneumatic gun designer start to scratch their heads, engineering design is possible but loading is impossible. My pneu friend got stuck at this for a year. Untill one day he told himself, damn what a dummy I am. The solution has been around us all this while. Since water is where the gun will be used, the medium to load the gun will be readily available to the hunter. Water is incompressible, that's the answer !!!!! He built a small hand held hydraulic pump using sea water as the pumping fluid. He used the water pressure to cock the piston in place....MAN,,,a genius !!! Hydraulic pump can pump tons of of pressure easy. The pump is only 40cm long and 1/4" diameter. With only under 30 strokes of the pump, the super pneu get cocked without ever using it's own shaft and it is so easy to do it because the power applied is bit by bit with the stroke of the pump. Same principal as hydraulic car jack but with no oil reservoir, the entire sea water is the fluid we ever need !!!
I weigh 72kg/158 pound. I tried loading his pneu with my entire body weight, the piston won't even move a bit.
This is the REAL key to his super power pneu, I might as well broadcast it here. As far as I know, no pneu in the world operate with 23mm piston because no one can ever load the gun but that kind of piston diameter is required to produce power output beyond belief. Yes, the firing barrel must be dry too, this is the second key to the power.
So this gun is a real dry firing pneu, can be use on land or in the water. Much work was done on the muzzle side because the shock damper that get banged by the piston must survived hell load of a job. The normal trigger found on say a Mares, can not be used on this kind of pneu. At certain pressure level, the trigger pull become offensive. The designer was having this trigger problem because I told him a blue water gun have to have a superb smooth release trigger. The last shot I did on land was using his newly designed trigger and it was nice. Designing a superb trigger on a pneu is not easy because everything must work in that air tight area of the 25ATM. Just imagine making a multi-stage trigger like an Alexander or Riffe unit and it must be air tight !!!!
If my friend lives in Italy, I am sure he will get hired by some speargun company.
I have tested the procedure of loading this gun. Pump it with the special pump, blow air into the barrel and place the shaft in. It does not take any longer than loading my gun with 4 x 5/8 bands. However, u need a place to store the pump and the small air hose. For freedivers you can always put it in ur float, for scubahunter a bit of extra hassle.
If ever such mass production of the super pneu is feasible, a lot of exotic metal will be required to keep it light and strong at the muzzle. Owing to the short 110cm to keep it agile and swing pretty, an 11-12mm shaft of 115-120cm will be required to transfer the massive energy.
If anyone interested in the design plan for mass production or whatever, I'll hook them to my friend. In my opinion nothing can be patended on the operation side of the gun like pumping with water to cock and o-ring on the shaft. Only the internal engineering ( already patent pending ) can be patended.
My friend does not own a machine shop, he is a computer guy. He has been in this pneu project for more than 3 years, out of love of spearfishing. I think his bank account been drained dry with all his experiment.
I want one of his gun but this is a slow refining process because he redesigned his unit when I give him ideas and a set of criterias and now he does not live in my city. Pneu gun is very complicated and can't be easily made by just anyone. Every part of this gun is stainless steel for the time being. So much work to be done just to alter a bit here and there. When everything satisfy me, I will then make one using a lighter weight material for my own use. Exotic metal or composite is not easy to get in my city.
Maybe another year boys ................
