*quiet* high fpe air guns

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For best quieting, it is best to have the valving shut before the pellet leaves the barrel. It is an interesting exercise to calculate some limits on where in the barrel the pellet could be. A dynamic calculation is beyond me, but treating the system as static, a minimum distance can be calculated. Taking the starting and finishing pressures of the reservoir, reservoir volume, and shot count of a string, a volume of air used per pellet can be calculated. In my case, 1 1/2 liters of air at atmsospheric pressure per Beast. Calculate the volume that that air would have at the regulated pressure, and compare that volume to the volume of the barrel (150 bar regulated air, 14.25 cc barrel vol.). This gives a result that the minimum distance the pellet can have traveled is 16 of the 24 inches of barrel (apt to be farther because of pressure drops due to flow dynamics and non-instantaneous valve action). So there's a scant 8 inches at best to shut off the air flow for best quieting. An additional point is that the pressure should be down to about 104 bar as the pellet exits the muzzle.

For comparison, RWS Hobby pellets in the same gun have a minimum shut off distance of 1.3 inches and should show an overpressure at the muzzle of 7.125 bar.
 
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"cernunnos"For best quieting, it is best to have the valving shut before the pellet leaves the barrel. It is an interesting exercise to calculate some limits on where in the barrel the pellet could be. A dynamic calculation is beyond me, but treating the system as static, a minimum distance can be calculated. Taking the starting and finishing pressures of the reservoir, reservoir volume, and shot count of a string, a volume of air used per pellet can be calculated. In my case, 1 1/2 liters of air at atmsospheric pressure per Beast. Calculate the volume that that air would have at the regulated pressure, and compare that volume to the volume of the barrel (150 bar regulated air, 14.25 cc barrel vol.). This gives a result that the minimum distance the pellet can have traveled is 16 of the 24 inches of barrel (apt to be farther because of pressure drops due to flow dynamics and non-instantaneous valve action). So there's a scant 8 inches at best to shut off the air flow for best quieting. An additional point is that the pressure should be down to about 104 bar as the pellet exits the muzzle.

For comparison, RWS Hobby pellets in the same gun have a minimum shut off distance of 1.3 inches and should show an overpressure at the muzzle of 7.125 bar.
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This good information. The math is way beyond my capabilities but what you've pointed out definitely makes sense. Thanks!
 
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I did Cernunnos's calculations for both my 47fpe .25 Wildcat, which has a 24" barrel and a 150bar regulator, and for my .22 sub 12fpe Wildcat, which has a 20" barrel and runs with a 60bar regulator.

Both came out at 13-14" minimum distance down the barrel, before the valve can shut off.

Both guns have about 4" of shroud beyond the muzzles (UK spec guns).

The sub 12 .22 WC is very, very, very quiet indeed.

The .25 WC is - erm - not, though I know most US airgunners think it is.

Bottom line is that the .25 discharges 3 times the mass of air at 2.5 times the pressure.
 
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