Air rifle max velocity vs. tank pressure

[JBA]

Doug Huffman suggested the possibility of locally choked flow. I tend to agree with that notion. Remember that you're dealing with a gas flow that is approaching Mach 1 --which at sea level should be around 1150 fps at the muzzle of the air-gun at standard atmosphere temperature and pressure.

My question is whether there is a sonic orifice after the needle valve that might limit the flow of gas into the breech of the gun. I don't know this specific model of airgun, but It seems to me that there ought to be such an orifice so as to keep the mass flow and velocity as consistent as possible.

My guess is that the gas flow from the tank will initially cause the tank and its gas to cool. This chilled gas will then admit more flow through the sonic orifice, until the pressure starts to drop. I suggest you try chilling the cylinder and filling it with cold gas and then compare that to a room temperature cylinder. I'm willing to bet that chilling the cylinder and gas will shoot the pellet faster than room temperature gas at the same pressure.

The problem with that concept is that the gas mass flow still increases essentially linearly with pressure after choked flow is achieved. Only the throat discharge velocity remains constant.