Expansion chamber

[rsterne]

The point I was trying to make is that the energy imparted to the pellet would be (significantly) less than that lost by expanding the CO2 to drive the piston.... It is entirely possible that you might not be able to achieve the same pellet velocity on CO2 alone, particularly using expansion of it.... We are probably talking about a loss of 80% using the compressed air piston, compared to an 85% loss trying to drive it just with CO2.... numbers for example only, not supposed to be accurate in any way....

I get that it may be possible, just not practical.... It might be more practical (and efficient) to use the CO2 to run a pressure booster, to fill a tank with air (to 4500 psi), to fill a PCP (to 4000 psi), to fire the pellet.... I wouldn't mind betting that a PCP at 4000 psi would beat any Springer (even a gas powered one) bigtime....

Bob

[Rob M]

all true Bob.. I do like the idea of a co2 powered booster charging a valve to 4000.

[rsterne]

As you know, I'm not all that much of a fan of dump valves, as they have to be large to have good power, and that makes them inefficient.... However, you could charge a conventional PCP (using a conventional timed valve) to whatever pressure you wanted to build it for by boosting the air in an SCBA tank using an air or CO2 powered booster.... Just remember that whatever you use to operate the booster is mostly lost energy....

Bob

[K.O.]

Do not know if it has any advantage over simply having a larger air reservoir ala Bobs Millennium Pumper... but the ANA Quigly used a air spring/differential piston...

https://www.americanairgunhunter.com/2015/03/ana-quigley-multi-pump-air-rifle/

[Insanity]

Ok so my thought is this convoluted rube goldberg thing, the numbers are irrelevant and just for the sake of discussion... So In the air reservoir you have say 3000psi then you have a spring of sorts in there that can produce 2900 pounds of opposite force that is so you can overcome the spring with air pressure when filling. Now the piston will move to the valve as you shoot not just once but incrementally with every shot maintaining 2900psi until you reach the end of the limited travel and then dump the air remaining. The piston will take up the volume of air exhausted as you shoot maintaining 2900psi. Next issue I see is the valve port may need to be kind of small so as to not have instant movement from the piston assembly messing your shot cycle up acting like a regulator in some way. 3rd issue I see is that this would take up a little less then half of the potential air volume available to use. 4th now you have more moving parts to fail and a heavier gun at the expense of more air volume.

[rsterne]

Springs require more force to collapse them further.... so to push the piston further along the reservoir would take more pressure.... Then as it moved back along the reservoir with each shot, the pressure would drop again.... You would not be creating a "constant pressure" as you desire.... Additionally, if you used a metal coil spring, it would have to be massive and therefore heavy to develop enough force.... An "air spring" would need your desired pressure inside when uncompressed.... and would still increase in pressure as it moved along the reservoir.... It might work OK if it was several FEET long, so that the percentage pressure change was relatively small....

Bob

[subscriber]

You guys are describing an infinitely large plenum.  As that is not feasible, a larger than standard plenum.  No bells, no whistles; and no springs or pistons...

[rsterne]

Or a PCP with a large reservoir (several cc's per FPE), tethered through a regulator to an SCBA tank....

Bob

[Insanity]

That's the problem you would need a progressive spring be it meal or gas that defies how a spring would really work. Also like I said it would be very bulky to contain both the air and device to make it work. To keep pressure constant a regulator is best no way to effectively keep it that way buy forcing it efficiently.

[MJP]

Why over complicate the design and add more inner recoil that adds to the poor harmonics of a hammer actuated pcp?

Marko