Marauder CO2 100% rated fill...and CO2+N2+O2

Joined: September 12th, 2011, 12:13 pm
The Marauder rifle CO2 "100% rated fill" (according to the commonly-posted reiser chart) is 5 ounces, correct?

Given:

- A fill of 2600-2800 psi (depending on fill temp) air or N2 (to allow 3000 psi@120F)
- A fill of 3.5 oz CO2 (70% fill) topped with air or nitrogen to 2150 psi (to allow 3000 psi@120F)

Which produces more consistent shot strings?

I think it depends on the rate at which each of N2, O2 and CO2 pass through the valve during each shot. I don't know how to derive the flow rates for each. I think each may depend on:
1. Either the partial pressure of each of the three gases, or the total pressure of all gases.
2. The relative densities - CO2 may flow more slowly since it is the most dense.

If 2. is true, then toward the end of a fill of air (only), you would have not have "air" left - the percentage of oxygen remaining would be notably higher than found in air. The repeated filling to 3000 psi, shooting to 2000 psi, refilling to 3000 psi, etc would seem to mean that at some point people who did this would be running at about 74% oxygen. I don't know how many fills it would take, but it is a low enough number to happen often in practice. I'm pretty sure this isn't happening, so I think 2. is not true; gases flow from high pressure to low pressure at a velocity independent of density.

Question 2: Which, if either, allows for greater efficiency (FPE per fill)? Here I have no idea where to begin.

Gas dynamics seems to be so complicated that my naive Google searches don't give links to the basics of flows of gas mixes.

Joined: May 12th, 2001, 1:29 pm
...have produced some interesting results, I think they're a very questionable idea, likely to produce fewer consistent shots than either gas by itself, and possibly being outright dangerous if exposed to temperature extremes.

JMO.

Steve

Joined: March 28th, 2002, 6:54 pm
The Marauder rifle CO2 "100% rated fill" (according to the commonly-posted reiser chart) is 5 ounces, correct?

Given:

- A fill of 2600-2800 psi (depending on fill temp) air or N2 (to allow 3000 psi@120F)
- A fill of 3.5 oz CO2 (70% fill) topped with air or nitrogen to 2150 psi (to allow 3000 psi@120F)

Which produces more consistent shot strings?

I think it depends on the rate at which each of N2, O2 and CO2 pass through the valve during each shot. I don't know how to derive the flow rates for each. I think each may depend on:
1. Either the partial pressure of each of the three gases, or the total pressure of all gases.
2. The relative densities - CO2 may flow more slowly since it is the most dense.

If 2. is true, then toward the end of a fill of air (only), you would have not have "air" left - the percentage of oxygen remaining would be notably higher than found in air. The repeated filling to 3000 psi, shooting to 2000 psi, refilling to 3000 psi, etc would seem to mean that at some point people who did this would be running at about 74% oxygen. I don't know how many fills it would take, but it is a low enough number to happen often in practice. I'm pretty sure this isn't happening, so I think 2. is not true; gases flow from high pressure to low pressure at a velocity independent of density.

Question 2: Which, if either, allows for greater efficiency (FPE per fill)? Here I have no idea where to begin.

Gas dynamics seems to be so complicated that my naive Google searches don't give links to the basics of flows of gas mixes.
but mostly one gas, will flow like the predominant gas. Gas blends don't separate under normal flow conditions, the molecules of low percentage gases are dragged along with the main gas, like leaves in a wind.

Joined: May 12th, 2001, 1:29 pm
...when liquid CO2 is present.

That's because liquid CO2 will evaporate to restore the CO2 partial pressure after each shot, but nothing similar happens for the air component. Therefore, the relative concentration of air, and therefore total pressure, would drop with each shot. Meanwhile, the concentration of CO2, and therefore average density, would rise.

What's worse, I think these effects would happen faster, making velocity fall off more quickly, than if the original fill had been 100% one gas or the other.

This is one reason I question whether CO2 + air mixtures can ever be superior to pure fills.

Steve