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Dag Evert's "American Classic"

As mentioned on the forum, heres a picture I took some time back, with natural winter daylight.
A 2100, and a 1377, both guns have been recrowned, and had their trigger parts shimmed for play,
contact surfaces stoned, and trigger springs somewhat reduced within safe limits.
The 2100 has had its barrel shimmed with tape to remove play.
Both guns give great accuracy for the money if they are given good pellets!
The combination of pellets and guns in the picture represents something close to my boyhood dreams:-)
-- Dag Evert

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Well, a couple of things.

July 5 2012 at 2:44 PM

Steve in NC  (Login pneuguy)
Crosman Forum Member
from IP address 74.242.231.138


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.

Steve

 
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