It looks like I misinterpreted the comment concerning the maximum pressure achievable in the "Alpha C1" gun as being 30 Bar (refer post#28). For that to happen the pump rod stroke length needs to be limited to 30 times the length of the dead space at the far end of the inner barrel, which in the "Alpha C1" serves as the hand pump bore, assuming that the volumes concerned both before and after the pump stroke are simply sections of the same diameter cylinder. However I have since learned that the spear shaft is used as the pump rod, which means that the piston can reach all the way back to the face of the closed off releasing valve. This results in a very small pumping dead space and hence the pressure level attained in the gun can be higher than 30 Bar. Bear in mind that a 14 mm diameter inner barrel represents a 16% increase in cross-sectional area over a 13 mm diameter inner barrel and a 62% increase in cross-sectional area over an 11 mm diameter inner barrel, hence the force required will be that much higher to push the pump handle down at the very end of the pumping stroke as the air transfers across into the outer tank. To reach 30 Bar that effort would be about 46 kg or 100 pounds on the pump handle, which indicates that 20 to 25 Bar is probably enough chamber pressure! Conversely the big bore inner barrel also means that less chamber pressure is required to shoot the spear with the same level of propulsive force, assuming that the extra water volume in the inner barrel can exit the muzzle without causing any offsetting loss of performance. The large muzzle relief ports are positioned close to the tip of the muzzle as the shock absorber is mounted on the front of the piston rather than mounted inside the muzzle body where the relief ports would have to be behind the "anvil" or "stopper" face.