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Tom West's Custom PC77 PumpMaster Classic Short Rifle

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Gas velocity - port hogging relationship

June 29 2012 at 8:23 PM
Airfierce  (Login Airfierce)
Crosman Forum Member
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I don't have much experience with airgun mods, also haven't been on the forums for quite a while.

I got to wondering about opening up ports. Seems that where you have a large volume chamber and a small orifice for air to pass through on its way to being exhausted, the restriction would work under the venturi effect. This would cause the gas to speed up exponentially at point of restriction, effectively causing a ram induction force into exhaust, increasing volume more quickly and speeding gas flow.

If that transfer port or whatever is opened up then there would be a loss of venturi effect and loss of gas velocity. Has any research or data crunching been done regarding this, to show where an intended improvement actually causes a net loss in pressure or gas velocity behind pellet? I can see advantage to smoothing contours or sharp edges however it seems there's a danger of backpedaling when hogging ports. Apologies if this has already been over thunk and discussed ad infinitum...

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