My deepest dive ( on scuba ) during my pneu days was at 140 feet for a 90cm model which I pumped at least 20% above reccomended setting. It shoot very poor this depth. At 175 feet there will be 90 psi of sea water pressure restricting the piston movement inside the pneu. A typical pneu get charged like 25-30BAR ( 370 - 450 psi ) on the surface. At 175, we have only about 280 to 360 psi pressure effective.
Since most pistons of pneu guns is between 11 to 13 milimeter in diameter, we can roughly calculate the actual amount of power available as propulsion is not the entrire 280 to 360 POUND PER SQUARE INCH cause 11-13mm or +-0.5 inch piston diameter is sure much less than 25.4 mm x 25.4 mm as in 1 SQ Inch.
Would you believe I forgot the formula to get total area of a circle.......must be narcosis:head.
Anyway assuming I am right...... I think there will be about 120 psi worth of real power to actualy push the shaft at these 175 feet deep. I don't know if we can translate that to a rubber gun of equivalent 120 pounds rubber pull, I suppose not. Hell I am lost too.
My experience told me that if the gun in question is long enough say 110 cm and uses thin 7mm ( 9/32) hawaiian shaft with very sharp tip and the shooter shoot from say 1 feet away even at 175 feet deep, I think a 4 inch flesh only penetration is possible but will it penetrate the hard head where it will stone the grouper, I don't know. Some shooters get very lucky you know...............
