Something to think about: noise/energy/air used per shot

[Ribbonstone]

I recently did go for a quiet .25 PCP.  Does use a large LDC. 

Hatsan, so the air tube is interchangeable between guns and I have a 14.4-foot pound .177 Hatsan. So I swapped air tubes (which includes the valve).



Same tube/valve that generates 14.4 foot pounds in .177 generates 23.4 foot pounds in .25.  No way I could interchange LDC’s (a .25 pellet though the .177’s LDC would just wreck the insides and a .177 pellet through a .25 designed LDC would let too much air pass though the larger holes). 

So I had to keep their respective LDC’s in place.  Know that gives the .25 an advantage, but there isn’t much I can do about it.

Result the 23.4 foot pound .25 is quieter than the 14.4 foot pound .177.

Lets look at the two shot counts.

177 Pnuema:



Which works out to about a FPE/cuin of 1.27 (or a BAR-cc/FPE of 12.9)

SAME AIR TUBE/VALVE on a .25 Hatsan: (using 31gr. pellets at about the same pressure range as above):



Which works out to about the same air use per shot (actually, a little bit better).

Some thoughts about that:

1. Same pressure range and same volume of air being used per shot. 
2. .Observation is that the .25 has about 80% more BASE AREA than the .177 pellet, and the increase in energy is about ½ that. Basically the same pressure has a larger area to push on, so transfer more energy.
3. With the larger bore volume, the air that is used per shot will exit the barrel at LOWER PRESSURE in .25 than in .177. Same air volume per shot filling a LARGE air volume ( a 20” .25 bore) will exit that barrel at lower pressure than a 20” .177 bore.
4.The energy the pellet carries has to come from somewhere, and the only somewhere is the air released from the shot.  So if the released air is the same and the pellet carries more energy, then the exiting air carries less.


It’s low energy for a .25, but impressively quiet. 

[rsterne]

Yep, quiet means efficient, in terms of residual muzzle pressure.... but you guys down south are spoiled with your LDCs....

Bob

[Ribbonstone]

Given  about the same barrel length, it does seem the best indicator of potential PCP noise is air use per shot rather than just looking at energy output.