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Dean's HiPac 2240

Tactical Trijicon ACOG TA01 Style 4x32 Cross Sight Rifle Scope + Kill Flash
TROBB Solid Aluminium Dovetail Power Block with Gmac hollow probe and G-mac Bolt
Gmac Brass Power Adjuster Spring And Guide/Drilled Out Standard Valve For more air space
Hammer Mods//Gmac 30% Lighter valve Spring/Gmac Brass Safety Catch//Transfer port drilled out
Full Gmac Trigger kit/Gmac barrel cut to 9inch/Weihrauch Silencer/Custom Home Made Grips/
New TRACER LEDRAY GL2 LAMP 90m Range Beam//HI-Pac

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Well, a couple of things.

July 5 2012 at 2:44 PM

  (Login pneuguy)
Crosman Forum Member
from IP address

Response to Question about the "Valve Ineffectiveness Chart"....

1. The basic idea behind "Sonic Horizon" was, due to the fundamental limit imposed by the speed of sound on the speed of propagation of pressure change, it makes no difference to the acceleration of the pellet whether the valve closes or remains open after the pellet crosses the "Horizon," because the pressure change created by the valve closing (or not) can't reach the pellet before it departs from the muzzle. In other words, the only gas that can contribute to accelerating the pellet in the example MV = 850fps case, is the gas occupying the first 33% of the bore. That is to say, 33% of the volume of the bore.

2. When air expands in an airgun, the expansion is so rapid that no significant heat has time to transfer from the walls of the bore etc. to the air. That is to say, the expansion is (to a good approximation) adiabatic. Under that condition, pressure isn't inversely proportional to volume, but (because air is effectively a diatomic gas) to volume raised to the 1.4 power. Therefore, for example, doubling volume wouldn't reduce pressure by factor of 2, but by 21.4 = 2.64.


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