What is that wisp of CO2 at the muzzle?
by B.B. Pelletier
This one comes from a comment made by Canadian reader Wild Wild West. "Speaking of whisps of CO2, I am not sure if you or any of the other Nightstalker owners have noticed, but on my Nightstalker with a fresh bottle and during the first 100 or so shots, I do get quite an annoying blast of CO2 following each shot."
Yes, you will see that on many CO2 guns, and today I'd like to examine why.
Liquid or gas?
The way some CO2 guns are designed - whether it's a full powerlet, removable bulk tank or new AirSource cartridge - it's possible for liquid CO2 to flow into the gun's valve when the gun is held level. The liquid CO2 cannot maintain its pressure once it's released from the confines of the tank, so it flashes to gas wherever it happens to be. If that is inside the valve of a gun or even beyond the valve and inside the gun's barrel, the CO2 does not have enough time to completely expand before it hits the outside air - still expanding. Because it cools as it expands, it instantly condenses the moisture in the air, creating a fog. The moister the air, the more fog is created.
Vertical vs. horizontal
If you look at AirSource guns, almost all of them align the cartridge horizontally, which means the liquid CO2 inside the full cartridge has the best chance of flowing out when the gun is fired. Now, the AirSource adapter upgrade kit, used to upgrade a standard Crosman 1077, positions the cartridge lower than the rifle's valve, preventing this from happening. The small amount of vertical space in the adapter allows CO2 gas to rise above the liquid and get to the valve first.
The Crosman NightStalker has the AirSource cartridge aligned horizontally in the butt, so it is a candidate for liquid to flow through the valve. A Benjamin EB 17 pistol has a 12-gram powerlet aligned horizontally with the valve in a tube at the front of the gun, so it is also a candidate for a wisp of fog with the first few shots from a fresh powerlet. On the other hand, a Colt Government Model M1911A1 pistol has the 12-gram powerlet aligned vertically inside the grip, so there is less chance of liquid passing through the valve. A gun like this is a lot less likely to have the wisp of fog from the muzzle on any but the hottest, most humid days.
What about the "dog days"?
There are days when the temperature is so high and the humidity is 100 percent that ANY CO2 gun is going to give a wisp of fog from the muzzle. On days like these, the air is completely saturated with moisture, and anything that changes the conditions for even an instant causes condensation. Just the relative coolness of the CO2 gas is enough to cause visible condensation on a day like this. Heck - even a PCP will smoke on some days for the same reason. I have seen water dripping from the wings of low-flying A10 Warthogs when they turn sharply close to the ground, simply from the air they compress ahead of the wing! They will actually leave brief vapor trails!
WHO - REALLY - CARES?
So what? Now that we know the science behind the smoke from CO2 guns - does it matter? As a matter of fact, it does. If an airgun is passing liquid - instead of gas - through the valve, you can expect the velocity to be way off the norm. If you chronograph the gun, that's exactly what you'll find. The first couple of shots from a CO2 gun - ESPECIALLY a gun with a horizontal tank - will be significantly faster than the norm. Then the gun will settle down to a long string of shots in close proximity until all the liquid is gone. Then, the velocity drops sharply.
So a target gun that uses CO2 will have a couple of wild shots before it settles down. That explains why the FWB C55 changed from a horizontal to a vertical gas tank and also why CO2 is not considered competitive at the world level anymore.
"Gee, Mr. Wizard, you sure can tell a lot of neat stuff from just a puff of gas at the muzzle of a gun!"
"Yes, Jimmy, you can."