by B.B. Pelletier

Before we start, there are 3 new articles on Pyramyd Air’s website:

  1. A look inside the BB gun powerplant
  2. Can you bend the barrel if you shoot a breakbarrel air rifle with the barrel broken open?
  3. What is a flyer?

So there I was on the set of American Airgunner. We were filming the CO2 episode, and Paul and I were shooting action pistols at tin cans. Paul had a Crosman 357 and I was shooting a tricked-out Beretta PX-4 Storm with all the bells and whistles. In the next take, we’d be shooting the cans with the camera behind us so we could be seen in the picture, along with the cans downrange.

I had just loaded a fresh CO2 cartridge because the last one ran out during the previous take. The camera started rolling, the director called, “Action!” and we started blasting away. I had one powerful shot and the next pellet came out so slow I could see it in flight. It barely made it to the cans 10 yards away. I kept pulling the trigger and the pellets kept dribbling out. What had happened?

Was the CO2 cartridge empty from the factory? Was it, heaven forbid, a leaker? These things flashed through me mind as the camera rolled, because I had just finished writing Fanner 50, and the memory of leaking CO2 cartridges was fresh in my mind, even though I hadn’t seen one in years.

When the shooting was over and the camera stopped rolling, I went to the equipment table, expecting to remove an empty cartridge. Instead, I exhausted an entire full cartridge! What had happened?

It doesn’t happen often, but sometimes the piercing pin pierces the CO2 cartridge only far enough for just the tiniest amount of gas to escape. When that happens, the gas comes out very slowly. If enough time elapses, the firing valve will fill to capacity and the first shot will be powerful, but all succeeding shots taken immediately afterward will be weak. However, if you wait about a minute, you’ll get another powerful shot followed by more weak ones. The CO2 molecule is very large compared to the atoms of the various gasses in air. So, air may flow well through tiny openings, but CO2 will not.

That evening, back in my room, while answering readers’ comments, I came across this one, attached to a report on how to find CO2 leaks:

“I have a Crosman 357 Co2 powered air pistol. I used WD-40 on the end of one air cartridge before knowing what sort of harm it would do to the airgun (that was a stupid idea).

Now the airgun is no longer consistent with each shot I fire. i.e. I fire one shot and its perfectly normal, then I fire another shot and the velocity of the pellet goes down by half etc… But when I wait for about 60 seconds after each shot the velocity of the pellet returns to normal. I don’t hear any leaks and I just got this gun about a month ago…

Would Crosman pellgunoil fix this problem? Or would this problem fix itself over time? What would you recommend?”

Those words brought the problem into sharp focus! Although I hadn’t thought about it much, I now remembered that this sort of thing happens from time to time, even with modern CO2 cartridges that are entirely reliable.

Here’s what I’m saying. The use of WD-40 is not recommended in a CO2 gun, but I’m not saying it had anything to do with your poor gas flow. I think you did what I did, by allowing the piercing pin to not penetrate the CO2 cartridge far enough to allow the gas to flow as it should. It could get out, which is why, after a minute or so, you have a powerful shot. But the next shot will be weak because the gas can’t flow fast enough to build the kind of pressure the gun was designed for.

Your problem with this gun is mechanical, and it may also be procedure-based. It’s mechanical because the pierced hole isn’t as large as it needs to be, and it may be based in a faulty procedure if you are not adjusting the piercing mechanism so that it pierces the cartridge in the way it was designed to.

In the 1960s, there used to be a special instruction in the manuals of some CO2 guns on how to effectively pierce cartridges. You were to screw the piercing cap down until you heard the hiss of escaping gas, then UNSCREW the cap a quarter turn, if you could. If the gas was not escaping fast enough, you would be able to easily unscrew the piercing cap, because the o-ring that sealed the gas in the gun was not under much pressure. Hence, the cap could turn. That was your signal to do something, which meant re-pierce the cartridge. However, if the pressure was high, that o-ring was tight against the side of the reservoir wall, making it impossible to turn the piercing cap by hand. That was the proof that the escape hole was large enough.

Piercing mechanisms have changed since those days, but the object has remained the same. Create a hole large enough for the CO2 gas to flow freely. Remember that each time you install a new cartridge. And oil each new cartridge with Crosman Pellgunoil–ONLY!