by Tom Gaylord
Writing as B.B. Pelletier

Part 1

This report covers:

• CO2 facts
• CO2 is a self-regulating gas
• The temperature thing
• Piercing pin problems
• Chilling bulk-fill guns to fill better
• Crosman Pellgunoil
• Automatic transmission stop leak
• Getting more power from a vintage CO2 gun

It took me long enough to get back to this report! I guess the SHOT Show and some other things just busied-up my schedule. But, this afternoon, I was installing a CO2 cartridge in a gun and had a little difficulty…when it hit me — I need to tell the readers about that! So, today I’ll talk about CO2 guns just a little.

When airgunner Jennifer Cooper Wylie asked for this report on my facebook page, I think she was looking for tuneup tips. I’ll give them, but mixed in will be some common maintenance tips, as well. We’re looking at CO2 guns today, and it’ll be helpful to remember what we know about CO2.

CO2 facts
CO2 is a refrigerant gas that expands as the temperature increases. When it expands, it increases in pressure when it’s in a confined space.

It’s also a gas that sublimates (changes from a solid to a gas without first becoming a liquid). It can be a source of thick, heavy fog used for theatrical effect without any special equipment being needed. Solid CO2 is simply placed in an open container like a bucket or tray and allowed to outgas. The dense fog flows out and hugs the floor because CO2 is heavier than air. If there’s water in the container, the outgassing speeds up, because water transfers its heat much faster than thin air.

CO2 is extremely cold in its solid and liquid forms. When it changes to gas, it does so by absorbing heat from its surroundings. Hence, as a CO2 gun fires, it gets colder. This chilling effect lowers the pressure of the resulting gas, so a gas gun fired rapidly also rapidly loses velocity. Since CO2 is used to power repeating airguns, this chilling effect needs to be taken into account. That’s why I allow a minimum of 10 seconds between shots when I test the velocity of a CO2 gun.

CO2 is a self-regulating gas
As a CO2 gun is fired, the liquid inside the cartridge (or the gun, itself, if it’s a bulk-fill gun) evaporates to replace the gas pressure that was used by the shot. At 70˚F, CO2 evaporates to a pressure of 853 psi. Just imagine that CO2 liquid expands 900 times when it changes to a gas. That’s why just 12 grams of CO2 liquid provides enough gas to power a gun for many shots.

In the old days, shooters thought their CO2 guns were leaking down fast. Many actually were because of the bottlecap CO2 cartridges then in use. But they were also experiencing a loss of velocity because they were shooting their guns rapidly and experiencing the chilling effect. Nobody talked about the chilling effect of CO2 in 1960 — people just chalked it up to gas leakage.

bottlecap CO2 cartridge
Crosman used this bottlecap method of sealing their cartridges for some time in the 1950s and ’60s to avoid patent infringement.

The temperature thing
Okay, let’s get on to today’s report. First, let’s talk about this temperature thing. It works both ways. On a cold day, when the ambient temperature is less than about 60˚F, a CO2 gun will chill with each shot and will not recover as fast. The colder it is, the slower the gun shoots. That’s why CO2 guns are not recommended for hunting in colder climates.

But it also works the other way. As the temperature rises, the gas pressure increases until you get what we call valve lock — too much pressure inside the valve for the striker to open it. I remember back in 2009 when we were filming a segment on action pistols for American Airgunner, and all our guns stopped working. We were filming in the Catskill mountains on a summer day where the temperature was just 85˚F. Normally, that’s an ideal temperature for a CO2 gun, but the guns that weren’t being used had been left on a table in bright sunshine — where they heated up to well over 100˚F. That’s when they all quit. When the second gun stopped working, I recognized what had happened and put the table in the shade for 30 minutes. After that, they all became operational, again.

Piercing pin problems
While filming this same segment, I found a couple guns that would fire one powerful shot and the next one was very weak. If we waited for a full minute, the next shot was powerful again. This wasn’t due to the gun chilling with the shot. This was something else.

When I removed the CO2 cartridge from the problem gun, I saw that the piercing pin had barely pierced the surface of the CO2 cartridge. It should have made a pronounced hole. The face seal in this particular gun was so thick that it prevented the piercing pin from piercing the cartridge as deeply as it was supposed to. Piercing pins are all the same at the factory, but there can be some variation in the thickness of synthetics used to make seals. Seals can also be made from different hardnesses (durometers) and that can cause the seal to not compress as it’s supposed to.

The solution was twofold. First, when we pierced the next cartridge, we put extra torque on the piercing screw to push the cartridge harder against the face seal. That squashed the seal down a little more. Then, we backed off on the piercing screw a small amount (1/4 turn) after the cartridge was pierced. That gave the gas more room to exit the cartridge.

This two-part approach worked in a limited way. That particular gun still took longer to recover from each shot than other guns, but the recovery time was now down to a few extra seconds instead of a whole minute. By repeatedly doing this procedure, you can eventually squash the thick face seal enough that the problem goes away entirely. This was the problem I had yesterday with the CZ P-09 pistol, and I fixed it exactly as I just described. If you shoot a lot of CO2 guns, you’ll eventually encounter one with this problem. Now you know how to deal with it.

Chilling bulk-fill guns to fill better
Bulk-fill CO2 guns are guns that are filled from an external tank instead of a throwaway cartridge. More equipment is involved, and it takes a few seconds longer to fill the gun, but the result is a gun that shoots 50 shots for 5 cents instead of 50 cents. That’s an almost 10-times reduction in the cost to shoot! Once I found that out, I became a lifelong advocate of bulk-fill CO2 guns.

But there are some things you have to know. When cold CO2 liquid enters a warm airgun reservoir, it immediately flashes to gas and increases the pressure inside the reservoir. Before long, the pressure in the reservoir is equal to the pressure inside the bulk tank that’s filling the gun. When that happens, the liquid stops flowing.

Chilling the gun before a fill lowers the temperature of the reservoir. Even when the liquid flashes to gas during filling, the temperature inside the reservoir is still lower than the temperature inside the CO2 filling tank, so the liquid continues to flow much longer. As a result, you get a higher percentage of liquid to gas inside the reservoir. This increases the number of shots you get per fill from about 30 for a room-temperature fill to 50 for a chilled fill.

But there’s some danger with this procedure. If the airgun is too cold, the percentage of liquid to gas in the gun’s reservoir can rise above 80 percent. When that happens, the space inside the gun for the CO2 to expand to gas is reduced, and that can have only one result — gas pressure rises. If the gun’s temperature rises like those action pistols we put in the sun, the pressure can exceed the strength of the materials used to build the gun. Then, the gun explodes!

So, chill your airgun or reservoir with this in mind. Either shoot the gun immediately or don’t fill it this way. A gun filled too full and left to sit is a time bomb whose clock can run out at any time.

Crosman Pellgunoil
I learned about Crosman Pellgunoil from Crosman repairman Rick Willnecker. He told me that he used Pellgunoil on every gun he resealed and that it’s impossible to use too much. When put on the tip of a CO2 cartridge or in the fill connection of a bulk-fill gun, the oil is blown into the gun’s valve where it gets on all the seals and o-rings, sealing them tight against gas loss.

Rick told me that many times when a customer sent him a gun for repairs, he first put some Pellgunoil into it and it sealed immediately. He still replaced all the seals because that was what the customer wanted, but he told me to give it a try. The opportunity came very quickly.

Edith and I used to attend a local flea market that was held in the parking lot of the local mall every Sunday. Once each month, they had Super Sunday and the number of stalls increased dramatically. A couple weeks after talking to Rick, I went to a Super Sunday and found 2 Crosman CO2 single-shot guns. One was a model 187 (.177) and the other was a model 180 (.22). They’re the same except for caliber. The seller told me they both leaked, but I knew Rick could reseal them so I bought both for $40, as I recall. When I got home I decided to try Rick’s suggestion, and he had given me some Pellgunoil sample packs to test.

I put Pellgunoil on the tips of 2 cartridges (each gun uses 1) and installed them. Both guns started leaking, then stopped suddenly. The 187 is scarce, and this one happened to be in excellent condition. I sold it for $100 but kept the 180. I still have it today, and it still holds gas indefinitely! I haven’t shot it in several years, so the cartridge that’s in it has been there for at least that long. I just pulled it out of the closet and fired a very powerful shot! Folks, that’s a testimonial to the benefits of Crosman Pellgunoil!

Automatic Transmission Stop Leak
But there’s something even better than Pellgunoil — Automatic Transmission Stop Leak. I wrote about this in a report titled, Neat fix for bulk-fill CO2 guns. That report was published 18 months ago, and the vintage bulk-fill pistol I fixed with that fluid still holds gas today. In fact, it has been holding for the past 18 months. Several naysayers warned that the seals would swell up and dissolve, but that hasn’t happened. And that gun was one I bought several years ago at an airgun show for very little money because it was a leaker! I couldn’t fix it with Pellgunoil, but this stuff did the job several years later. If it hadn’t worked, the gun could still have been resealed.

Getting more power from a vintage CO2 gun
Okay, Jennifer, here’s a tip for you. Many vintage CO2 guns have adjustable power that their owners overlook. All the Crosman bulk-fill rifles and pistols have these adjustments, but even some of the guns that use CO2 cartridges have them, too. The Crosman Mark I and II pistols have a power screw in front of their frame, as well as 2 different stops for the cocking knobs; the Crosman 180s have a tiny Allen screw that’s reached through their cocking knobs. Even the S&W 78G and 79G pistols have power screws below their muzzles.

So, boosting the power of your vintage CO2 gun may be as easy as turning the power screw higher. That can be a most welcome discovery when it applies to a vintage gun that you already enjoy.