Can a CO2 gun work with air?
by B.B. Pelletier
We got the following question posted to Friday's blog:
"This question is both for the Chinese Crosman copy [the QB 78] and the Drozd. Is there a way to convert such weapons to use compressed air, such as a fillable tank?
The quick answer is yes, a CO2 gun can be made to run on air. As long as the pressure of the air is not too different than the pressure at which CO2 normally operates (853 psi at 70 degrees F), then the valve will open with the same hammer weight and spring strength. Once open, the thinner air, which is comprised of several elemental gasses, flows through the valve faster than the large CO2 molecule, so the velocity will spike. Because the air flows more freely, more air than CO2 gas will flow. The pressure will drop faster, resulting in fewer shots. Also, the CO2 in a reservoir is a liquid that evaporates into gas, maintaining the pressure of the gas. Pressurized air is just a gas; and when it's gone, there's nothing to replace it.
It's been done many times
I'm sure this has been done by many experimenters, but the first one I'm aware of was one that Dennis Quackenbush did in the mid-1990s. A .22 caliber Quackenbush Excel that got about 650 f.p.s. on CO2 jumped to over 800 f.p.s. on air. An air reservoir of nearly the same size as the CO2 paintball tank got far fewer shots per fill, but enough to make the experiment worthwhile.
Air Arms S200
You may be more familiar with the Air Arms S200 PCP rifle. It started life as a Tau 200 CO2 target rifle that several American field target shooters decided would make a good PCP gun. At the time, the rifle was selling for about $275. Several people began converting Tau 200s into PCP rifles, and they worked well enough that they caught the attention of Air Arms. They contracted with the Czech factory to produce the rifle under their name, and the S200 was born. By passing through another set of hands and with the increase of the euro against the dollar, the price has risen quite a bit.
Several years ago the Steyr company contracted to make their popular 10-meter target pistol, the LP1, into a CO2 gun with Barbara Mandrell's name on it. Starting in 1999, It was sold through the NRA to raise money for USA Shooting, the American Olympic contingent. Steyr used a CO2 valve and a CO2 tank. Why the gun was requested in CO2 is a mystery, since PCPs had taken over the world stage when the pistol was first offered, but Steyr also offered the parts kit to change the gun to a PCP through Steyr dealer Scott Pilkington. Though 250 were scheduled for production, the actual number produced was probably close to 100, because the price was perhaps too high for non-airgunners.
The Barbara Mandrell Steyr pistol was available in either CO2 or PCP.
Both the QB78 and the Drozd have been converted to air
These days, making such conversions is easier because of the paintball crowd and their constant-air technology. They have regulators to lower air pressure for the firing valves in their markers to 850 psi, which makes a gun run just as efficiently on air as it would CO2. By controlling the volume of the firing chamber, they can also control the potential power of the gun. As long as the valve can pass only a certain volume of air, it cannot exceed a certain power level regardless of the valving it has. It doesn't become more powerful on air than on CO2.
This paintball technology transfers over to airguns very nicely. It's been done on the experimental level, and the small production level with the QB78 and the Drozd, but no big company has yet employed it. I think they will, when somebody realizes the potential for greater sales.